- Email: [email protected]
Structural analysis and luminescence studies of Ce3+: Dy3+ co-doped calcium zinc gadolinium borate glasses using EXAFS
Journal Pre-proof 3+ 3+ Structural analysis and luminescence studies of Ce : Dy co-doped calcium zinc gadolinium borate glasses using EXAFS R. Rajaramakrishna, Y. Ruangtaweep, S. Sattayaporn, P. Kidkhunthod, S. Kothan, J. Kaewkhao PII:
S0969-806X(19)31255-1
DOI:
https://doi.org/10.1016/j.radphyschem.2020.108695
Reference:
RPC 108695
To appear in:
Radiation Physics and Chemistry
Received Date: 27 September 2019 Revised Date:
23 December 2019
Accepted Date: 6 January 2020
Please cite this article as: Rajaramakrishna, R., Ruangtaweep, Y., Sattayaporn, S., Kidkhunthod, P., 3+ 3+ Kothan, S., Kaewkhao, J., Structural analysis and luminescence studies of Ce : Dy co-doped calcium zinc gadolinium borate glasses using EXAFS, Radiation Physics and Chemistry (2020), doi: https://doi.org/10.1016/j.radphyschem.2020.108695. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.
Author Statement Dr. R. Raja Ramakrishna: Conceptualization, Methodology, Data Analysis, Original draft preparation, Prof. Dr. Jakrapong Kaewkhao: Conceptualization, Methodology, Supervisor. Dr. Y. Ruangtaweep: Synthesis of glass, Dr. S. Sattayaporn and Dr. P. Kidkhunthod: Synchrotron facility, Analysis of XANES and EXAFS Dr. S. Kothan: Funding and Discussion through out the work
Structural analysis and Luminescence studies of Ce3+: Dy3+ co-doped calcium zinc gadolinium borate glasses using EXAFS R. Rajaramakrishnaa, Y. Ruangtaweepa,*, S. Sattayapornb, P. Kidkhunthodb, S. Kothanc, J. Kaewkhaoa,** a
Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000, Thailand b
c
Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, 30000, Thailand
Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai 50200, *
Email: [email protected]
**
Email: jakrapong@[email protected] , [email protected]
Abstract: Ce3+: Dy3+- codoped calcium zinc gadolinium borate glasses were synthesized by traditional melt quenching technique. These glasses after synthesizing they were characterized through density, molar volume, refractive index, FTIR, absorption spectra, photoluminescence properties, structural studies using XANES/EXAFS and life time profile analysis. XANES spectra of Gd LIII-edge and Dy LIII-edge for 20CaCO3 - 20 ZnO - 10Gd2O3 - 49.5B2O3 - 0.5Dy2O3 (C2) and 20CaCO3 - 20 ZnO - 10Gd2O3 - 49B2O3 - 0.5Dy2O3 - 0.5CeF3 (D) glass showed absorption edge at 7249.8 eV and 7795.7 eV respectively confirming the presence of Gd3+ and Dy3+ ions. Ce-LIII edge for D glass shows peaks at ∼ 5728 eV confirming the presence of Ce3+. The Judd-Ofelt (JO) theory investigations have been applied for Dy3+ ions to calculate the Judd-Ofelt (JO) intensity parameters and found that the trend follows Ω2> Ω4> Ω6. The ionic nature of RE3+-O were evaluated by using bonding parameter (δ) value for C2 and D glass and found to be -0.0076 and -0.0102. Radiative properties were subsequently estimated using JO parameters and investigated radiative transition probabilities (AR), stimulated emission cross section (σR) and branching ratio (βR). The photoluminescence and radio luminescence spectra exhibit two prominent emission peaks at 484 (blue) and 575 nm (yellow) that corresponds to the4F9/2→6H15/2 and4F9/2→6H13/2 transitions respectively. The chromaticity coordinates were evaluated and found that these coordinates positioned in the white region with (x, y) = (0.348 0.382) and (0.325, 0.353) values for C2 and D glasses. The florescence decay from the 4F9/2 level was measure by monitoring the intense 4F9/2 to 6H9/2 transition. The decay time is found to be bi-exponential when monitored at λexi=387nm. The results obtained in present work demonstrate that the present glasses could be potential candidate for use in white light solid state lighting applications.
Key words: Judd-Ofelt theory, Photoluminescence, X-Ray luminescence, XAS spectra, EXAFS analysis.
1. Introduction Glass is material which provides enough room to investigate with their multi-functional characteristics behavior when doped with rare-earth oxides. Next generation is emerging from Light-emitting diodes (LEDs) as one of the solid-state lighting (SSL) devices which have shown potential for the replacement of its conventional counterpart such as incandescent light bulbs and fluorescent lamps. Judd-Ofelt intensity parameters, Ωλ (λ = 2, 4 and 6), some important dynamic parameters such as radiative transition rates, oscillator strengths, fluorescence lifetimes, fluorescence branching ratios and quantum efficiencies can be confirmed. Judd-Ofelt calculation, some fundamentals should be strictly assured: a) the electron in all the excited state levels can be quickly relaxed to the emitting level, in this sense it is possible to obtain an excitation spectrum having the same spectral line shape with the absorption spectrum; b) the obtained excitation spectrum should be intensity-calibrated to remove the deviation in spectral line shape from the absorption spectrum induced by the different detector and instrument responses (Zhang et al., 2018). Also based on the semiconductor light emitting, laser diodes (LDs) have characteristics of monochromaticity, polarization and parallelism on beam quality due to coherent phase photon emission (Zang et al., 2017). Dysprosium being topic of interest in recent decade due to their intense blue and yellow emission originating from 4F9/2 to 6H15/2 and 6H13/2 respectively when excited by UV source (Khan et al., 2019c). The surroundings in the region of Dy3+ ion is strongly influencing the hypersensitive transition (4F9/2 to 6H13/2) leading to variation in their yellow to blue emission intensity ratio. Dy3+ ions emission spectrum consists of strong bands corresponding to the 4F9/2 → 6H15/2 (blue) and 4F9/2 → 6H13/2 (yellow) transitions accompanied by transition in the visible range. Numerous Dy3+-doped glass systems were investigated and studied for obtaining white light through appropriate combinations of these luminescent band intensities and two primarycolored luminescent materials especially Y/B variations (Shasmal and Karmakar, 2019). In this paper we focus on the two primary colored luminescent transitions to obtain pure white light. Introduction of Gd3+ ions acts as a sensitizer and enhances the luminescence intensity and also influences for energy transfer characteristics (Rajaramakrishna et al., 2020; Ravangvong et al., 2020). Many literatures show energy transfer phenomenon when co-doped with two or more
rare-earth ions (Zheng et al., 2011) and host itself in the form of charge transfer band (CTB) (Tian et al., 2013). Introduction of Ce3+ ions which were co-doped in gadolinium dysprosium alkaline earth borate glasses which affects photoluminescence emission and tailor their white luminous due to Y/B ratio from Dy3+ doped glasses under the appropriate excitation suggesting a promising and efficient optical devices for laser illumination as well as the color coordinates which are evaluated from CIE color coordinate diagram (Tian et al., 2013) and correlated color temperature (CCT) of white fluorescence to anticipate their cool warm temperature by the color due to the rare-earth.
2. Investigational procedure Glass fabrication Glasses with 10g batch as a starting raw material with high purity of 99.99% AR grade calcium carbonate (CaCO3), zinc oxide (ZnO), gadolinium tri-oxide (Gd2O3), orthoboric acid (H3BO3), dysprosium tri oxide (Dy2O3) and cerium fluoride (CeF3) were used to synthesis according to glass formula 20CaCO3-20ZnO-10Gd2O3-(50-x)B2O3-Xmol%Dy2O3 (X = 0.3 (C1 glass), 0.5 (C2 glass), 1.0 (C3 glass) mol%) and 20CaCO3-20ZnO-10Gd2O3-49B2O3-0.5Dy2O3-0.5CeF3 (D glass) using muffle furnace. The samples were polished into 10mm×5mm×3mm thickness. Absorption and photoluminescence studies were performed for the prepared samples. The chemical composition and sample codes are presented in Table 1. Characterization Techniques Refractive index was calculated using Abbe refractometer (ATAGO) with sodium vapor lamp (598.3 nm (D line)) as mono bromo naphthalene being contact liquid. UV-Vis-NIR spectrometer (Shimadzu, UV-3100) was used to determine the absorption spectra ranging from 2200 nm to 200 nm wavelength. Photoluminescence and lifetime decay analysis of the prepared samples were measured Cary Eclipse fluorescence spectrometer (Agilent technologies Inc). X-ray induced luminescence were measured by using X-ray generator with 50kv voltage and 30mA current at room temperature. Synchrotron studies were carried in SLRI (Synchrotron Light Research Institute Thailand). 3. Physical Properties
Density of the prepared samples were measured by applying Archimedes principle which were obtained using the relation (Rajaramakrishna et al., 2014). From Table.2 the density of the glass increases with increase in Dy3+ concentration due to higher molecular weight of the Dy3+ ion which replaces Boron atom in the glass matrix as well as Dy3+ ion concentration also increases with increase in the Dy2O3. Whereas density increases with co-doping of Dy3+ + Ce3+ and molar volume decreases suggesting that they yield rigidity or structure compactness in the glass matrix. It is observed from Table 2 that decrease in polaron radius (rp) from 0.999 nm to 0.669 nm with increase in concentration of Dy3+ ions which is ascribed to yield rigidity in structure or tighten around Dy3+ ion inside host matrix. When co-doped with Dy3+ + Ce3+ ions they show similar trend. Such compactness of the structure could affect the luminescence intensity of the glass. 4. Analysis of absorption spectra The absorption studies of 20CaCO3-20ZnO-10Gd2O3-(50-x) B2O3 glasses doped with various concentration of Dy2O3 are calculated in UV-Vis and NIR region are shown in Fig.1. The spectra consists of ten absorption peaks position at 384, 425, 452, 472, 750, 801, 900, 1088, 1269 and 1678 nm originating from lower level of 6H15/2 to the higher level of 4I(3)13/2, 4G(4)11/2, 4I(3)15/2, 4
F(3)9/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2,6F11/2 and 6H11/2 for Dy3+ ion. With increasing concentration of
Dy2O3 content the absorption intensity of all the transition increases. For Dy3+ ions 6F11/2 have highest intensity and is found to be hypersensitive(Khan et al., 2019b; Shasmal and Karmakar, 2019; Zang et al., 2017). Table 3 shows JO parameters for C2 and D glass and are found to be Ω2=1.1035, Ω4=0.3430, Ω6=0.4663 and Ω2=1.0398, Ω4=0.3009, Ω6=0.5265 (x 10-20 cm2) respectively. The JO parameters follow Ω2 > Ω6 > Ω4 showing elevated values than other reported as shown in table.4 and follows the same fashion compared with other literatures PBZLBD (Zulfiqar Ali Ahamed et al., 2013) LPABD (Deopa and Rao, 2017) PTBD (Vijaya Kumar et al., 2012) PBAWD (Pisarska, 2009) ZNBBD1 (Hegde et al., 2019) BiZNBD (Shanmugavelu and Kumar, 2014) LFBPD (Balakrishna et al., 2012). 4.1 Judd-Ofelt parameters and Radiative properties The experimental oscillator strength (fexp) were studied from absorption spectrum by using the following formula (Judd, 1962; Ofelt, 1962). Judd-Ofelt Ωλ (λ =2, 4, 6) is the intensity parameter were obtained using reported literature (Balakrishna et al., 2012; Deopa and Rao, 2017; Hegde et
al., 2019; Pisarska, 2009; Rajaramakrishna et al., 2014; Shanmugavelu and Kumar, 2014; Zulfiqar Ali Ahamed et al., 2013). The Ωλ parameters have been derived from the electric-dipole contribution of the experimental oscillator strengths using a least square fitting approach (Khan et al., 2019a, 2018; Kirdsiri et al., 2019, 2018; Shoaib et al., 2019b, 2019a). JO- intensity parameters are used to determine the radiative properties such as transition probability (AR), branching ratio
, stimulated emission cross section (σ(λp)).
4.2. Nephelauxetic effect In lanthanides the f-shell being partially half filled due to their covalent character of the rareearth oxygen bonding which can be determined by nephelauxetic effect. Nephelauxetic ratio (β) is used to determine the nature of Dy3+ ligand bond using the relation (C.K. Jorgensen, 1962, SINHA, 1966). =
(1)
Where υa and υc is the wave number (cm-1) of particular corresponding transition of rare earth ion in the aqua-ion (Carnall et al., 1968) and in the title glass respectively. Bonding parameter (δ) is calculated from the average value of β by =
(
)
(2)
The δ value for C2 and D glass is found to be -0.0076 and -0.0102 which indicate the ionic nature of RE3+-O bonding due to their negative value and found that D glass shows more ionic than C2 glass. The available NBO's could open up the network wide to form Ln3+- O more ionicity in D glass as compared to C2 glass, the ionicity could be due to the oxygen vacancy near Ln3+-O which is confirmed with XAS results discussed in section.8. Since this is confirmed from the JO intensity Ω2 parameter where D glass show less value than C2 glass suggesting the asymmetry of the Dy3+ ions (Rajaramakrishna et al., 2014). It is clear that in the present glasses the covalency asymmetry around the Dy ions is altered by their neighboring counterpart such as Gd3+ ions or Ce3+ ions. From Table 3 it can be seen that stimulated emission cross section σ (λP) is found to be higher as compared to other reported literature, 5. Photoluminescence Excitation spectra (λemi = 575 nm):
The excitation spectra of C2 and D glass shown in Fig.2 was monitored at 575 nm Dy3+ emission wavelength. These glasses show prominent signature excitation peaks of corresponding rareearth ions and also charge transfer bands at 200-225 nm. In C2 glass it was observed 10 prominent peaks in which 2 peaks corresponding to Gd3+ ions at 254 nm (8S7/2→6DJ) and 275 nm (8S7/2→6I11/2). Remaining 8 peaks corresponding to Dy3+ ions 312, 325, 351, 365, 387, 426, 452 and 473 nm from ground state 6H15/2 →6P3/2+4M11/2, 4I9/2, 6P7/2, 4I11/2+6P5/2, 4I13/2+6F7/2, 4G11/2, 4
I15/2, 4F9/2 respectively. Whereas in D glass sample a prominent broad excitation peak was
observed at 315 nm corresponding to Ce3+ via parity allowed 4f (2F5/2) →5d absorption. 6. Photoluminescence Emission spectra of Dy3+ (λexi = 387 nm): The Fig.3 exhibits the PL emission spectra of C series and D glasses. All the glass samples were excited with 387 nm in the spectral range of 400 nm to 700 nm. The spectra exhibit three prominent emission peaks at 484 (blue), 575 nm (yellow) and 665 nm (red) that corresponds to the4F9/2→6H15/2,
4
F9/2→6H13/2 and
4
F9/2→6H11/2 transitions respectively as
displayed in Fig.4. In addition, transition located at 665 (red) attributed to 4F9/2→6H11/2 (Khan et al., 2019c; Shasmal and Karmakar, 2019; Zang et al., 2017). Radiative properties for fluorescent levels, 6H15/2, 6H13/2 and 6H11/2 of Dy3+ glasses have been estimated and presented in table 4. By substituting the known values of Sed and Smd radiative transition probabilities (AR) and in turn total radiative transition probability (AT), radiative lifetimes (τrad), branching ratios (βr) and absorption cross-sections for stimulated emission (σ(λp)) have been calculated 6H15/2, 6H13/2 and 6
H11/2 of Dy3+ ions. From Table 4 it can be seen that stimulated emission cross section σ (λP) is
found to be higher as compared to other reported literature (Hegde et al., 2019; Khan et al., 2019b; Ravangvong et al., 2019; Shanmugavelu and Kumar, 2014; Vijaya Kumar et al., 2012; Zulfiqar Ali Ahamed et al., 2013). Concentration quenching is observed at 0.5 mol% Dy3+ content, this is due to opening of cross relaxation channels (CRC) and resonance energy transfer (RET) in non-radiative transition as shown in Fig.4. The opening of cross-relaxation channels is the common process observed in the Dy3+ doped glasses where the excitation energy is transferred from one active Dy3+ ion in excited state (4F9/2) to the nearby ground state (6H15/2) Dy3+ ion which excites from the ground state to the intermediate state termed as CRC1, CRC2 and CRC3 which are as shown in the Fig.4 (Riseberg. L .A, 1977)(Dexter and Schulman, 1954; Zhong et al., 2008).
Electric dipole
transition is due to dependent of the local surroundings around Dy3+ ions and magnetic dipole transition is due to independent to the local surroundings around Dy3+ ions (Ma et al., 2015; Yan and Huang, 2007). The radiative properties of C2 and D glasses were obtained and values are tabulated in Table 3. The likelihood to achieve enough stimulated emission from particular transition for lasing action could be explained with branching ratio which should exhibit larger than 0.5 value to consider for their potential use for lasing emission (Maruyama et al., 2009). The transition from 4
F9/2 state to 6H13/2 state has branching ratio value (βR) 0.70 for C2 glass sample and 0.69 for D
glass sample suggesting their potential use for laser emission, moreover the value well agrees with experimental and calculated branching ratio (βR) value show 0.50 for all transitions of C2 and D glass samples. The energy transfer rate (WET) was calculated and found to be 24.68 S-1 and 4.208S-1 for C2 and D glass respectively. The multi phonon relaxation rate (WMPR) is not considered due the difference of energy gap is ~10000 cm-1 between 4F9/2 to 6H11/2. From the energy transfer rate, it is clear that D glass show less energy transfer rate suggesting that more probability of the back transfer (BT1) process. The excitation energy (387 nm) of Dy3+ ion and emission energy (372 nm) of Ce3+ ions overlaps in the form of resonance energy transfer (RET). 4
F9/2 → 6H13/2 transition being highest compared to other transition and hence it signifies the
capability of the transition for laser action. 7. Photoluminescence Emission spectra of Ce3+ (λexi = 315 nm): In the present case rare earths such as Gd3+, Ce3+ and Dy3+ are especially suitable for energy transfer and back transfer phenomenon due to these Ln3+ ions provide narrow electronic levels to which absorption occurs and from which fluorescence is observed. Symbolically, energy transfer can be written as 2(S)→1(S)→1(A)→2(A) or S*+A→S+A* When the active donor Ln3+ ions de-excited from higher excited state of 2(S) to the lower lying ground state 1(S), the energy transfer occurs which is released to bring an activator Ln3+ ions from the lower lying ground state 1(A) to its higher excited state 2(A). Energy transfer phenomenon from donor (Ce3+) to acceptor (Dy3+) plays an important role in luminescence. It is important to get different regions of the visible spectrum in a matrix in which different activation ions can be structurally active for cation sites (Gedam et al., 2013). The Ce3+-related photoluminescence emission and excitation spectra obtained for sample D are shown in Fig. 5.
The excitation at 315 nm, exhibits broad 5d1 → 4f (2F5/2, 2F7/2) emission of Ce3+ ions centered at 372 nm and through radiative energy transfer (ET1) signature peaks of Dy3+ ions at 484 nm (4F9/2 → 6H15/2) and 575 nm (4F9/2 → 6H13/2) emission were observed. These glasses contain Gd2O3 content hence, the Ce3+ excitation and emission were shifted slightly (within ∼5-7 nm) from other reported literature (Rathaiah et al., 2019), possibly due to the change in structural lattice around Ce3+ ions which gets localized. 8. Photoluminescence Emission spectra of Gd3+ (λexi = 275 nm): From fig. 6(a-b) when monitored at 275 nm excitation the lodged charge transfer band (CT) energy is promoted by 205 nm to 6G7/2 level of Gd3+ ions (as shown in Fig.2) subsequently the Gd3+ emission occurs from 6G7/2→6P7/2 level at 15,948 cm−1 (627 nm) with stokes shift from excitation source energy. Obviously the higher excited 4f multiplets of Gd3+ in visible-ultraviolet range play an important role in the transfer characteristics process: (a) Gd3+ to Ce3+ in UV range and (b) Gd3+ to Dy3+ in Visible range. Transfer Characteristics:
Monitoring at 275 nm, the Gd3+ ions excite to 6IJ state and
then non radiatively depopulates to the 6P7/2 level. (a) The UV emission at 315 nm (Fig.6(a)) corresponding to 6P7/2 → 8S7/2 transition is observed in C2 and D glass respectively. The emission at 315 nm decreases with addition of CeF3 concentration. The broad emission peak at 372 nm were observed in D glass corresponding to 5d1 → 4f (2F5/2, 2F7/2) transition whereas, this peak was absent in C2 glass. Such emission is classic example of energy transfer phenomenon (ET2) from 6P7/2 to 5d1 level of Ce3+ ions as depicted in Fig.4. (b) The visible emission (Fig.6(b)) corresponding to Dy3+ ions at 484 nm (4F9/2 → 6H15/2), 575 nm (4F9/2 → 6H13/2) and 664 nm (4F9/2 → 6H11/2) transitions. The emission of Dy3+ ions were observed when monitored Gd3+ ions showing complete energy transfer phenomenon (ET3) as depicted in Fig.4. In fact, the exchange between Ce3+ ↔ Gd3+ energy transfer phenomenon is achievable at all Ce/Gd concentrations. However, when the concentration of Gd3+ ions are less (i.e., Gd < 20%), the ET from Gd3+ to Ce3+ is more effective, due to the overlap of the Gd3+ emission peak at 315 nm (6P7/2→8S7/2) with Ce3+ absorption at 315 nm (4f - 5d), resulting in the increase of the Ce3+ emission [28] and decrease in Dy3+ emission as observed from Fig.6(a-b).
9. Yellow to Blue (Y/B) emission intensity ratio: The value of Y/B ratio is determined from luminescence transition of 4F9/2 → 6H13/2 transition (575 nm) to 4F9/2 → 6H15/2 transition (482 nm) for different excitation wavelength as shown in Table 5. The radiative transition takes place from 4F9/2 giving rise to intense blue and yellow emission. These intense emission bands arise as the energy difference between the states lying above 4F9/2 (21000 cm-1) is minutely small, and there is large separation (~6000 cm-1) between 4F9/2 and the next lower state 6F1/2 as shown in Fig.4. In addition to this, high phonon energy of the present glass system is another important parameter for such intense visible emission. The value of Yellow to Blue (Y/B) ratio increases with increase in Dy2O3 content when monitored at 387nm, whereas it decreases with addition of CeF3 content. When compared to C2 and D sample the Y/B ratio for both these glasses decreases when monitored for 387 nm for Dy3+ ions and 275 nm for Gd3+ ions. The data were compared with other reported literature which shows higher than (Vijaya Kumar et al., 2012; Vijaya et al., 2013; Zulfiqar Ali Ahamed et al., 2013) and less than (Khan et al., 2019c ; Shanmugavelu and Kumar, 2014). The data suggests that C2 and D glass shows higher covalence around Dy3+ ions and Gd3+ ions respectively. While the Y/B ratio can also be influenced due to glass composition, rare earth ion concentration and excitation wavelength 10. Lifetime Analysis: The luminescent transition 4F9/2 state of Dy3+ ion is acquired by exciting at 387 nm and emission at 575 are obtained and presented in table.6. The decay curves were fitted to different exponential equations, and the best fit was observed for the bi-exponential equation for C2 and D glass samples. The biexponential fit indicates that the interaction between rare earth ions becomes prominent, and the energy transfer process takes place from an excited Dy3+ ion (donor) to an unexcited Dy3+ ion (acceptor) (Linganna et al., 2015). The intensity of the luminescence spectra is given by literature (Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, 2005) = =
+
+ exp −
exp − +
+ ! exp
! exp
−
"
− +
(13)
"
# exp
−
$
(14)
where, I and Io represent the luminescence intensities at time t and 0, τ1, τ2 and τ3 represents the two (equation 13) and three (equation 14) components of the lifetime, corresponding to the fast and slow lifetimes for exponential components, respectively; A1, A2 and A3 are fitting constant, and t is the time. The calculated values of the average decay time (tavg) is found to be biexponential (equation 13 and 15) 0.578ms and 0.567ms for C2 and D glass respectively. The value of average decay time has been determined by the following formula (Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, 2005): %&'( =
)
" *) " " "
%&'( =
)
" *) " *) " " " $ $
)
)
*)" "
*)" " *)$ $
(15) (16)
It can be observed that the average lifetime decreases with addition of CeF3 content, which indicates the existence of energy transfer process between donor and acceptor as explained in section 5, 6 and 7. Ce3+ lifetime was also calculated using three exponentials (equation 14 and 16) and found to be 10.21 ns. The experimental decay lifetime and quantum efficiency (η=τexp/τrad) of luminescent 4F9/2 level using reported literatures (Rasool et al., 2013; Srihari and Jayasankar, 2017; Vijaya et al., 2013). The quantum efficiency found to be 0.858 and 0.860 for C2 and D glass samples respectively for Dy3+ ions. The efficiency found to be higher than (Hegde et al., 2019; Shanmugavelu and Kumar, 2014; Zulfiqar Ali Ahamed et al., 2013) and less than (Ravangvong et al., 2019).
11. X-Ray luminescence spectra From the Fig.8(a), the X-ray induced emission spectra of C2 and D glasses were synthesized with same cylindrical shape (1cm diameter) as that of BGO crystal so that it can be compared and these glasses were irradiated with X-ray at 50 kV and 20 mA. From Fig.9, the excitation source was x-ray, the spectral results were nearly identical to those obtained from the photoluminescence. From the Fig. 9, strong blue (482 nm) and yellow (575 nm) peaks were observed. In addition, from Fig.8(b), the white light emission could now be directly observed by naked eyes in the dark chamber when illuminated with UV lamp, and hence suggested that the developed glass could have been utilized and proved large potential in X-ray detections. The
ultraviolet excitation can directly activate the active luminescent ions, while the X-ray excitation would activate the holes and electrons from the host (glass) matrix. With the X-ray excitations, the secondary electrons are readily created, and eventually excite, either indirectly or directly.
12. CIE chromaticity Diagram The Commission Internationale de l'Elcairage (CIE) chromaticity diagram for the synthesized glass samples are shown in Fig.10 when excited at 387nm. In particular, the C2 and D glass sample shows white light emission with CIE color coordinates (x=0.348, y=0.382) and (x=0.325, y=0.353) respectively, which are close to those of the standard white light (0.3333, 0.3333), indicating that the glass is suitable for white light emitting device applications. The uncertainty in the color coordinates when monitored at 387nm shows around ±1%. The superiority of light can be evaluated in terms of the correlated color temperature (CCT) (M.N.Khan, 2013). Depending upon application fair values of CCT which ranges from 3500-6500 K which is acceptable for commercial purpose. McCamy existential formula use the color coordinates to calculate CCT values for the prepared glass samples (McCamy, 1992). The CCT value for C2 and D glass were found in the range of 4986 K and 5812 K at +,-. = 387 nm respectively. These CCT values for studied glasses shows slightly greater than the standard warm (CCT = 4000 K) (Kaewkhao et al., 2016), but D glass coordinates almost center of the white region. 13. XANES Analysis The Gd LIII-edge white line XANES spectra, resulted from a 2p3/2 → 5d excitation is very intense, which makes this spectrum susceptible to absorption effects when collected in fluorescence mode (Hess et al., 2002; Materlik et al., 1983). Fig.11(a) shows the XANES spectra of Gd LIII-edge for C2 and D glass, indicating the absorption edge at 7249.8 eV. In Fig.11(b), the Dy LIII-edge white line XANES spectra of the C2 and D glasses were nearly identical, demonstrating the sharp absorption peak (white line) at 7795.7 eV. The white line intensity when monitored for Gd ion (7249.8 eV) shows increased intensity for C2 glass whereas decreases in the case of Dy ion (7795.7 eV). This spectral change shows that the near neighbor environment of Gd / Dy undergoes rearrangement: either increased atomic order and/or a
more ionic character of the Gd-O bond, implying that the average Gd-O bond length increases in C2 as compared to D glass samples due to the increase in its white line intensity as shown in table.7. Furthermore, the intensity of white line is inversely proportional to oxygen vacancy. Moreover, we collected XANES spectra of the Ce-LIII absorption edge as shown in Fig.11(c). Under electric field, the amplitude and integrated area of the prominent Ce-LIII peaks at ∼ 5728 eV (the “white line”) increases with time, reaches a maximum and then levels off. Compared to the XANES spectrum of the pure Gd2O3, Dy2O3 and CeF3 standard samples, the energy difference of the white line and edge positions were less than 0.4 eV. Therefore, the XANES data confirmed that the oxidation states of Gd, Dy and Ce ions in the C2 and D glass found to be +3. 14. EXAFS Analysis monitored for Gd3+ / Ce3+: EXAFS spectra of D glass samples were obtained to study more details in terms of interatomic distance, coordination number and disordered structure. EXAFS spectra were Fouriertransformed into R-space. EXAFS in R-space of C2 and D glass samples were presented in Fig 12 and Fig.13 when probed for Gd atom. Similarly, EXAFS in R-space for D glass sample were presented in Fig.14 when probed for Ce atom. To investigate their local structure, Artemis program was utilized for fitting the structure data to the experimental spectra. The fitting results of C2 and D glass sample were shown in table.7. Regarding C2 and D glass, several standard model structures were tested such as GdBO3 (Orthorhombic, Hexagonal, Trigonal), Gd2O3 (Monoclinic, Trigonal, Cubic, Tetragonal), CeF3 (Hexagonal, Trigonal) and Ce2O3 (Monoclinic, Trigonal). The best fit was obtained by using the structures of the standard database of Gd2O3 3 c1) and Ce2O3 (Cubic-la33). The (Cubic-la33), GdBO3 (Orthorhombic-Ama2), CeF3 (Trigonal-P3 corresponding R-factor were between 0.01-0.02, indicating high accuracy and reliability for EXAFS analysis. Table 7, shows atomic distances (R), coordination numbers (N), Debye-Waller factors (4 ! ), amplitude reduction (56! ) and R-factor of C2 and D glasses.
Here in the present work we observed oxygen coordination number for C2 and D glass to be 6 in number. There are 2 inequivalent oxygen species, 2 oxygens and 4 oxygens with radial distances of 2.293 and 2.425 Å for C2 glass. Whereas D glass showed the radial distances were 2.342 and 2.584 Å. For D glass the experimental spectrum can be best fit by using different
model structure. However, we observe slight expansion in Gd-O and Gd-Gd bond lengths. The inter-atomic distance between Gd-O (coordination 6) and Gd- Gd are significantly higher in C2 glass than compared with D glass. However, the greater values of σ2 in D glass signifies higher atomic displacement. Ce3+ ions present in D glass are found to be coordinated with 7 fluorides and 6 oxygen's in the first shell. The fit data are reported in Table 7. Altogether, the results confirm that the Gd-O or Gd-Gd distance is less in D glass than in C2 glass thus signifying their efficient energy transfer characteristics. Conclusions The investigation carried out reveals a strong PL emission of Dy3+ ions was observed at 484 nm and 575 nm corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively in C2 and D glass samples when monitored at 387, 315 and 275 nm excitation. A broad PL emission of Ce3+ ions was observed at 372 nm in D glass corresponding to 5d1 → 4f (2F5/2, 2F7/2) transition when monitored at 315 and 275 nm excitation. An energy transfer phenomenon was observed from Ce3+ → Dy3+ ions. Also, a back-transfer phenomenon was observed from Dy3+ → Ce3+ ions when monitored at 387. A strong emission of Gd3+ ions were observed at 315 nm and weak emission at 627 nm corresponding to 6P7/2 → 8S7/2 and from 6
G7/2→6P7/2 transition respectively in C2 glass but these peaks were less intense in D glass. The
quantum efficiency was obtained and found to be 0.858 and 0.860 for C2 and D glass samples respectively for Dy3+ ions. X-ray luminescence shows strong blue (482 nm) and yellow (575 nm) peaks and exhibits intense white light when illuminated with UV lamp. The CCT value were evaluated for C2 and D glass were found in the range of 4986 K and 5812 K at +,-. = 387 nm respectively. XANES spectra of Gd LIII-edge, Dy LIII-edge and Ce LIII-edge for C2 and D glass showed absorption edge at 7249.8 eV, 7795.7 eV and ∼ 5728 eV suggesting that these glasses shows +3 oxidation state. EXAFS analysis shows that the inter-atomic distance between Gd-O and Gd-Gd are significantly longer in C2 glass when compared with D glass supporting their efficient energy transfer and back transfer mechanism. Ce3+ ions in D glass are coordinated with 4 fluorides and 6 oxygen's in the first shell.
Acknowledgment
Author (R. Rajaramakrishna) would express deep gratitude to supervisor Dr. Jakrapong Kaewkhao. The authors would also like to express gratitude to Nakhon Pathom Rajabhat University and National Research Council of Thailand (NRCT) for financial supports of this work. This research was partially supported by Chiang Mai University.
References Balakrishna, A., Rajesh, D., Ratnakaram, Y.C., 2012. Structural and photoluminescence properties of Dy3 doped different modifier oxide-based lithium borate glasses. J. Lumin. 132, 2984–2991. https://doi.org/10.1016/j.jlumin.2012.06.014 Carnall, W.T., Fields, P.R., Rajnak, K., 1968. Electronic Energy Levels in the Trivalent Lanthanide Aquo Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+ 4424. https://doi.org/10.1063/1.1669893 Deopa, N., Rao, A.S., 2017. Photoluminescence and energy transfer studies of Dy3+ ions doped lithium lead alumino borate glasses for w-LED and laser applications. J. Lumin. 192, 832– 841. https://doi.org/10.1016/j.jlumin.2017.07.052 Dexter, D.L., Schulman, J.H., 1954. Theory of concentration quenching in inorganic phosphors. J. Chem. Phys. 22, 1063–1070. https://doi.org/10.1063/1.1740265 Gedam, S.C., Dhoble, S.J., Park, K., 2013. Resonant energy transfer from Ce 3+ →Dy 3+ and Mn 2+ in NaZnSO 4 Cl chlorosulphate phosphor. J. Lumin. 139, 47–51. https://doi.org/10.1016/j.jlumin.2013.02.010 Hegde, V., Chauhan, N., Viswanath, C.S.D., Kumar, V., Mahato, K.K., Kamath, S.D., 2019. Photoemission and thermoluminescence characteristics of Dy 3+ -doped zinc sodium bismuth borate glasses. Solid State Sci. 89, 130–138. https://doi.org/10.1016/j.solidstatesciences.2019.01.002 Hess, N.J., Begg, B.D., Conradson, S.D., McCready, D.E., Gassman, P.L., Weber, W.J., 2002. Spectroscopic investigations of the structural phase transition in Gd2(Ti1-yZry)2O7 pyrochlores. J. Phys. Chem. B 106, 4663–4677. https://doi.org/10.1021/jp014285t Judd, B.R., 1962. Optical Absorption Intensities of Rare-Earth Ions. Phys. Rev. 127, 750–761. Kaewkhao, J., Wantana, N., Kaewjaeng, S., Kothan, S., Kim, H.J., 2016. scintillating glasses. J. RARE EARTHS 34, 583–589. https://doi.org/10.1016/S1002-0721(16)60065-0 Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, J.L., 2005. Luminescence and energy transfer of Eu- and Mn-coactivated CaAl 2Si2O8 as a potential phosphor for whitelight UVLED. Chem. Mater. 17, 3883–3888. https://doi.org/10.1021/cm050638f Khan, I., Rooh, G., Rajaramakrishna, R., Sirsittapokakun, N., Kim, H.J., Kaewkhao, J., Kirdsiri,
K., 2019a. Energy transfer phenomenon of Gd 3+ to excited ground state of Eu 3+ ions in Li 2 O-BaO-Gd 2 O 3 -SiO 2 -Eu 2 O 3 glasses. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 210, 21–29. https://doi.org/10.1016/j.saa.2018.11.008 Khan, I., Rooh, G., Rajaramakrishna, R., Sirsittipokakun, N., Kim, H.J., Wongdeeying, C., Kaewkhao, J., 2018a. Development of Eu3+ doped Li2O-BaO-GdF3-SiO2 oxyfluoride glass for efficient energy transfer from Gd3+ to Eu3+ in red emission solid state device application. J. Lumin. 203, 515–524. https://doi.org/10.1016/j.jlumin.2018.07.009 Khan, I., Rooh, G., Rajaramakrishna, R., Srisittipokakun, N., Kim, H.J., Kaewkhao, J., Ruangtaweep, Y., 2019b. Photoluminescence Properties of Dy3+ Ion-Doped Li2O-PbOGd2O3-SiO2 Glasses for White Light Application. Brazilian J. Phys. https://doi.org/10.1007/s13538-019-00695-0 Khan, I., Rooh, G., Rajaramakrishna, R., Srisittipokakun, N., Wongdeeying, C., Kiwsakunkran, N., Wantana, N., Kim, H.J., Kaewkhao, J., Tuscharoen, S., 2019c. Photoluminescence and white light generation of Dy 2 O 3 doped Li 2 O-BaO-Gd 2 O 3 - SiO 2 for white light LED. J. Alloys Compd. 774, 244–254. https://doi.org/10.1016/j.jallcom.2018.09.156 Kirdsiri, K., Raja Ramakrishna, R., Damdee, B., Kim, H.J., Kaewjaeng, S., Kothan, S., Kaewkhao, J., 2018. Investigations of optical and luminescence features of Sm3+ doped Li2O-MO-B2O3 (M =Mg/Ca/Sr/Ba) glasses mixed with different modifier oxides as an orange light emitting phosphor for WLED’s. J. Alloys Compd. 749, 197–204. https://doi.org/10.1016/j.jallcom.2018.03.266 Kirdsiri, K., Rajaramakrishna, R., Damdee, B., Kim, H.J., Nuntawong, N., Horphathum, M., Kaewkhao, J., 2019. Influence of alkaline earth oxides on Eu 3+ doped lithium borate glasses for photonic, laser and radiation detection material applications. Solid State Sci. 89, 57–66. https://doi.org/10.1016/j.solidstatesciences.2018.12.019 Linganna, K., Sreedhar, V.B., Jayasankar, C.K., 2015. Luminescence properties of Tb3+ ions in zinc fluorophosphate glasses for green laser applications. Mater. Res. Bull. 67, 196–200. https://doi.org/10.1016/j.materresbull.2015.02.062 Ma, Q.L., Zhai, B.G., Huang, Y.M., 2015. Effect of sol-gel combustion temperature on the luminescent properties of trivalent Dy doped SrAl2O4. Ceram. Int. 41, 5830–5835. https://doi.org/10.1016/j.ceramint.2015.01.012 Maruyama, N., Honma, T., Komatsu, T., 2009. Enhanced quantum yield of yellow photoluminescence of Dy3+ ions in nonlinear optical Ba2TiSi2O8 nanocrystals formed in glass. J. Solid State Chem. 182, 246–252. https://doi.org/10.1016/j.jssc.2008.10.028 Materlik, G., Müller, J.E., Wilkins, J.W., 1983. L-edge absorption spectra of the rare earths: Assessment of the single-particle picture. Phys. Rev. Lett. 50, 267–270. https://doi.org/10.1103/PhysRevLett.50.267 McCamy, C.S., 1992. Correlated color temperature as an explicit function of chromaticity coordinates. Color Res. Appl. 17, 142–144. https://doi.org/10.1002/col.5080170211
Ofelt, G.S., 1962. Intensities of Crystal Spectra of Rare‐Earth Ions, The Journal of Chemical Physics. https://doi.org/10.1063/1.1701366 Pisarska, J., 2009. Optical properties of lead borate glasses containing Dy3+ ions. J. Phys. Condens. Matter 21. https://doi.org/10.1088/0953-8984/21/28/285101 Rajaramakrishna, R., Knorr, B., Dierolf, V., Anavekar, R. V, Jain, H., 2014. Spectroscopic properties of Sm 3 þ -doped lanthanum borogermanate glass. J. Lumin. 156, 192–198. https://doi.org/10.1016/j.jlumin.2014.07.021 Rajaramakrishna, R., Nijapai, P., Kidkhunthod, P., Kim, H.J., Kaewkhao, J., Ruangtaweep, Y., 2020. Molecular dynamics simulation and luminescence properties of Eu 3 þ doped molybdenum gadolinium borate glasses for red emission. J. Alloys Compd. 813, 151914. https://doi.org/10.1016/j.jallcom.2019.151914 Rasool, S.N., Rama Moorthy, L., Jayasankar, C.K., 2013. Optical and luminescence properties of Dy 3+ ions in phosphate based glasses. Solid State Sci. 22, 82–90. https://doi.org/10.1016/j.solidstatesciences.2013.05.013 Rathaiah, M., Kucera, M., Pejchal, J., Beitlerova, A., Kucerkova, R., Nikl, M., 2019. Epitaxial growth, photoluminescence and scintillation properties of Gd3+ co-doped YAlO3:Ce3+ films. Radiat. Meas. 121, 86–90. https://doi.org/10.1016/j.radmeas.2018.12.013 Ravangvong, S., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Kaewkhao, J., 2020. Effect of sodium oxide and sodium fluoride in gadolinium phosphate glasses doped with Eu2O3 content. J. Lumin. 116950. https://doi.org/10.1016/j.jlumin.2019.116950 Ravangvong, S., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Sangwaranatee, N., Kaewkhao, J., 2019. Dy3+ ions doped (Na2O/NaF)-Gd2O3–P2O5 glasses for solid state lighting material applications. Solid State Sci. 97, 105972. https://doi.org/10.1016/j.solidstatesciences.2019.105972 Shanmugavelu, B., Kumar, V.V.R.K., 2014. Luminescence studies of Dy3+ doped bismuth zinc borate glasses. J. Lumin. 146, 358–363. https://doi.org/10.1016/j.jlumin.2013.10.018 Shasmal, N., Karmakar, B., 2019. White light-emitting Dy 3+ -doped transparent chloroborosilicate glass: synthesis and optical properties. J. Asian Ceram. Soc. 7, 42–52. https://doi.org/10.1080/21870764.2018.1555883 Shoaib, M., Rooh, G., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Wongdeeying, C., Kaewkhao, J., 2019a. Intriguing energy transfer mechanism in oxide and oxy-fluoride phosphate glasses. Opt. Mater. (Amst). 88, 429–444. https://doi.org/10.1016/j.optmat.2018.11.059 Shoaib, M., Rooh, G., Rajaramakrishna, R., Chanthima, N., Kiwsakunkran, N., Kim, H.J., Kaewkhao, J., Tuscharoen, S., 2019b. Comparative study of Sm3+ ions doped phosphate based oxide and oxy-fluoride glasses for solid state lighting applications. J. Rare Earths 37, 374–382. https://doi.org/10.1016/j.jre.2018.09.008 SINHA, S.P., 1966. Complexes of the Rare Earths. Complexes Rare Earths 17–23.
https://doi.org/10.1016/b978-0-08-011616-7.50005-x Srihari, T., Jayasankar, C.K., 2017. Fluorescence properties and white light generation from Dy3+-doped niobium phosphate glasses. Opt. Mater. (Amst). 69, 87–95. https://doi.org/10.1016/j.optmat.2017.04.001 Tian, B., Chen, B., Tian, Y., Li, X., Zhang, J., Sun, J., Zhong, Haiyang, Cheng, L., Fu, S., Zhong, Hua, Wang, Y., Zhang, X., Xia, H., Hua, R., 2013. Excitation pathway and temperature dependent luminescence in color tunable Ba5Gd8Zn4O21:Eu3+ phosphors. J. Mater. Chem. C 1, 2338–2344. https://doi.org/10.1039/c3tc00915g Vijaya Kumar, M. V., Jamalaiah, B.C., Rama Gopal, K., Reddy, R.R., 2012. Optical absorption and fluorescence studies of Dy 3 -doped lead telluroborate glasses. J. Lumin. 132, 86–90. https://doi.org/10.1016/j.jlumin.2011.07.021 Vijaya, N., Upendra Kumar, K., Jayasankar, C.K., 2013. Dy3+-doped zinc fluorophosphate glasses for white luminescence applications. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 113, 145–153. https://doi.org/10.1016/j.saa.2013.04.036 Yan, B., Huang, H., 2007. Sol-gel synthesis and luminescence of unexpected microrod crystalline Ca5La5(SiO4)3(PO4)3O2:Dy3+ phosphors employing different silicate sources. Opt. Mater. (Amst). 29, 1706–1709. https://doi.org/10.1016/j.optmat.2006.09.004 Zang, X.M.Z., Un, E.Y.B.P., In, H.L., 2017. Dy 3 + doped borate glasses for laser illumination 7, 4585–4591. Zhang, Y., Chen, B., Xu, S., Li, X., Zhang, J., Sun, J., Zhang, X., Xia, H., Hua, R., 2018. A universal approach for calculating the Judd-Ofelt parameters of RE3+ in powdered phosphors and its application for the β-NaYF4:Er3+/Yb3+ phosphor derived from autocombustion-assisted fluoridation. Phys. Chem. Chem. Phys. 20, 15876–15883. https://doi.org/10.1039/c8cp02317d Zheng, Y., Chen, B., Zhong, H., Sun, J., Cheng, L., Li, X., Zhang, J., Tian, Y., Lu, W., Wan, J., Yu, T., Huang, L., Yu, H., Lin, H., 2011. Optical transition, excitation state absorption, and energy transfer study of Er3+, Nd3+ single-doped, and Er3+/Nd 3+ codoped tellurite glasses for mid-infrared laser applications. J. Am. Ceram. Soc. 94, 1766–1772. https://doi.org/10.1111/j.1551-2916.2010.04323.x Zhong, J., Liang, H., Han, B., Tian, Z., Su, Q., Tao, Y., 2008. Intensive emission of Dy^3+ in NaGd(PO_3)_4 for Hg-free lamps application. Opt. Express 16, 7508. https://doi.org/10.1364/oe.16.007508 Zulfiqar Ali Ahamed, S., Madhukar Reddy, C., Deva Prasad Raju, B., 2013. Structural, thermal and optical investigations of Dy3+ ions doped lead containing lithium fluoroborate glasses for simulation of white light. Opt. Mater. (Amst). 35, 1385–1394. https://doi.org/10.1016/j.optmat.2013.02.006
Table.1. Sample code and compositions Main Code: Sample Code:
C
D
Compositions
C1
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.7B2O3 - 0.3Dy2O3
C2
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.5B2O3 - 0.5Dy2O3
C3
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.0B2O3 - 1.0Dy2O3 20CaCO3 - 20 ZnO - 10Gd2O3 - 49B2O3 - 0.5Dy2O3 - 0.5CeF3
Table.2 Physical Properties of Dy3+ doped glasses Dy3+
Dy3+ / Ce3+
Physical Property 0.3
0.5
1.0
0.5 / 0.5
Density, ρ (g/cm3)
3.7804 3.8171 3.8632
3.8423
Molar Volume
26.309 26.215 26.294
26.209
Refractive index, nd ( =589.3 nm)
1.6546 1.6543 1.6541
1.6540
Dy3+-ion concentration (N ×1020ions/cm3) 0.6867 1.1487 2.2905
1.1490
Polaron Radius (rp) (×10-9 m)
0.9992 0.8419 0.6690
0.8418
Inter-atomic Radius (ri) (A˚)
2.4456 2.0602 1.6369
2.0601
Field Strength (×1016)
3.370
7.516
4.747
Dielectric Constant (ε)
2.7377 2.7367 2.7360
2.7357
Molar Polarizability (RM)
9.6499 9.6117 9.6386
9.6060
1.2748 7.6185 3.8199
7.6141
Electronic Polarizability (
)
4.747
Table.3. Judd-Ofelt parameters, experimental (fexp x 10-6) and calculated (fcal x 10-6) oscillator strength for C2 and D glass sample. Wavelength Energy
C2 Glass
D Glass
(nm)
(cm-1)
I(3)13/2
384
26041
1.2028 1.5289
G(4)11/2
425
23529
0.5137 0.1344 0.4716 0.1194
4
452
22123
1.7900 0.9031
472
21186
2.2060 0.3423 0.9681 0.3773
Transition 4 4
I(3)15/2
4
F(3)9/2
fexp
fcal
fexp
fcal
-
-
-
-
6
F3/2
750
13333
2.4360 0.3889 1.5340 0.4390
6
F5/2
800
12500
3.6000 2.0575 3.1840 2.3228
6
F7/2
900
11111
3.5830 4.4550 4.0415 4.8959
6
F9/2
1088
9191
5.1590 5.0031 5.3640 5.1921
F11/2
1269
7880
12.610 12.596 12.240 12.259
H11/2
1678
5959
2.4420 2.5481 2.8950 2.7494
Ω2
1.1035
C2 Glass (×10-19 cm2)
Ω4
0.3430
∆rms = ± 0.990
Ω6
0.4663
β
1.0077
δ
-0.0076
Ω2
1.0398
Ω4
0.3009
Ω6
0.5265
β
1.0104
δ
-0.0102
6 6
D Glass (×10-19 cm2) ∆rms = ± 0.632
Table 4. Radiative properties of C2 and D glass. Level 4
4
λp
∆λeff
AR
σ (λp) (x 10-20 cm2)
βr Exp
Cal
F9/2 → C2 Glass 6
H15/2
482
16.29
440.31
1.1176
0.49
0.20
6
H13/2
575
16.44
1425.3
6.8296
0.50
0.70
6
H11/2
665
9.35
149.82
0.7212
0.01
0.06
F9/2 → D Glass 6
H15/2
482
16.39
489.11
0.5837
0.48
0.21
6
H13/2
575
18.91
1412.81
4.8265
0.50
0.69
6
H11/2
665
15.71
144.13
0.7894
0.01
0.06
AT of 4F9/2 : (C2glass =2015.4 ; Dglass =2046.0), τrad : (C2glass =0.496 ms ; Dglass =0.488 ms)
Table.5 Emission intensity ratio of C and D glass samples. Glass Y/B Ratio (λexi= 387 nm) Y/B Ratio (λexi= 315 nm) Y/B Ratio (λexi= 275 nm) Dy3+ ions
Ce3+ ions
Gd3+ ions
C1
1.069
-
-
C2
1.075
-
1.024
C3
1.078
-
-
D
1.055
0.921
0.924
Table.6 Lifetime of C2 and D glass samples λexi = 275 nm
λexi = 387 nm
λexi = 315 nm
λemi = 575 nm λemi = 575 nm
λemi = 370 nm
Two-exponential
Three-exponential
Wavelength
Samples C2 Glass
0.683 ms
0.578 ms
-
D Glass
0.557 ms
0.567 ms
10.21 ns
Table. 7 EXAFS fitting parameters of Gd3+, atomic distances (R), coordination numbers (N), Debye-Waller factors (
), amplitude reduction ( ) and R-factor of C2 and D glass.
Samples Paths C2
D
D
N
(
) R(Å)
Gd-O(1)
2
1.039 0.005
2.982
2.293
Gd-O(2)
4
1.039 0.010
2.982
2.425
Gd-Gd(1)
4
1.039 0.024
2.982
4.108
Gd-O(1)
4
0.8
0.002
4.9
2.342
Gd-O(2)
2
0.8
0.011
4.9
2.584
Gd-Gd(1)
4
0.8
0.016
4.9
3.755
Gd-F(1)
8
0.8
0.030
4.9
2.531
Gd-F(2)
6
0.8
0.032
4.9
2.923
Gd-Gd(2) 12
0.8
0.031
4.9
4.134
Ce-O(1)
6
1
0.024
-4.922
2.380
Ce-Ce(1)
6
1
0.011
-4.922
3.913
Ce-F(1)
2
1
0.004
-4.922
2.238
Ce-F(2)
3
1
0.002
-4.922
2.472
Ce-Ce(2)
6
1
0.017
-4.922
4.248
Ce-F(3)
2
1
0.003
-4.922
2.654
R-factor 0.019
0.010
0.011
Fig.1. Absorption spectra of C2 glass
Fig.2. Excitation spectra of Dy3+/Ce3+ doped glasses (Monitored at λemi=575nm)
Fig.3. Emission spectra of Dy3+/Ce3+ doped glasses (Monitored at λexi=387nm)
Fig.4. Complete Energy transfer process of Gd3+/Ce3+/Dy3+ ions in the present glass system.
Fig.5. Emission spectra of C2 and D glass (Monitored at λemi=372 nm and λexi=315 nm).
Fig.6. Emission spectra of Dy3+/Ce3+ doped glasses (Monitored at λexi=275nm) (a) UV range (b) Visible range
Fig.7. Lifetime spectra of C2 and D glass samples.
Fig.8 (a) Glasses used to record X-ray luminescence spectra (b) Glasses illuminated in UV lamp.
Fig.9. X-ray luminescence spectra of C2 and D glass samples.
Fig.10. CIE spectra of C2 and D glass samples.
(a)
(b)
(c)
Fig. 11. XANES spectra of C2 and D glass probing for (a) Gd3+ (b) Dy3+ (c) Ce3+
Figure. 12 EXAFS fitting spectra in R-space of C2 glass sample probed for Gd.
Figure. 13 EXAFS fitting spectra in R-space of D glass sample probed for Gd.
Fig.14. EXAFS fitting spectra in R-space of D glass sample probed for Ce.
Research Highlights 1. Photo-luminescence properties of Dy3+ / Ce3+ doped 20CaCO3-20ZnO-10Gd2O3-49B2O3 glasses were investigated. 2. Transfer characteristics of Gd3+ → Dy3+ and back transfer characteristics of Dy3+ → Ce3+ ions were analyzed. 3. Radioluminescence spectra were analyzed and found to be similar to that of photoluminescence. 4. XANES analysis were employed to understand the oxidation state of rare-earth ions embedded in the glasses. 5. EXAFS fitting was employed using artemis program and well fitted with the standard model to understand their coordination number.
Conflict of interest: None
S0969-806X(19)31255-1
DOI:
https://doi.org/10.1016/j.radphyschem.2020.108695
Reference:
RPC 108695
To appear in:
Radiation Physics and Chemistry
Received Date: 27 September 2019 Revised Date:
23 December 2019
Accepted Date: 6 January 2020
Please cite this article as: Rajaramakrishna, R., Ruangtaweep, Y., Sattayaporn, S., Kidkhunthod, P., 3+ 3+ Kothan, S., Kaewkhao, J., Structural analysis and luminescence studies of Ce : Dy co-doped calcium zinc gadolinium borate glasses using EXAFS, Radiation Physics and Chemistry (2020), doi: https://doi.org/10.1016/j.radphyschem.2020.108695. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.
Author Statement Dr. R. Raja Ramakrishna: Conceptualization, Methodology, Data Analysis, Original draft preparation, Prof. Dr. Jakrapong Kaewkhao: Conceptualization, Methodology, Supervisor. Dr. Y. Ruangtaweep: Synthesis of glass, Dr. S. Sattayaporn and Dr. P. Kidkhunthod: Synchrotron facility, Analysis of XANES and EXAFS Dr. S. Kothan: Funding and Discussion through out the work
Structural analysis and Luminescence studies of Ce3+: Dy3+ co-doped calcium zinc gadolinium borate glasses using EXAFS R. Rajaramakrishnaa, Y. Ruangtaweepa,*, S. Sattayapornb, P. Kidkhunthodb, S. Kothanc, J. Kaewkhaoa,** a
Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000, Thailand b
c
Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, 30000, Thailand
Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai 50200, *
Email: [email protected]
**
Email: jakrapong@[email protected] , [email protected]
Abstract: Ce3+: Dy3+- codoped calcium zinc gadolinium borate glasses were synthesized by traditional melt quenching technique. These glasses after synthesizing they were characterized through density, molar volume, refractive index, FTIR, absorption spectra, photoluminescence properties, structural studies using XANES/EXAFS and life time profile analysis. XANES spectra of Gd LIII-edge and Dy LIII-edge for 20CaCO3 - 20 ZnO - 10Gd2O3 - 49.5B2O3 - 0.5Dy2O3 (C2) and 20CaCO3 - 20 ZnO - 10Gd2O3 - 49B2O3 - 0.5Dy2O3 - 0.5CeF3 (D) glass showed absorption edge at 7249.8 eV and 7795.7 eV respectively confirming the presence of Gd3+ and Dy3+ ions. Ce-LIII edge for D glass shows peaks at ∼ 5728 eV confirming the presence of Ce3+. The Judd-Ofelt (JO) theory investigations have been applied for Dy3+ ions to calculate the Judd-Ofelt (JO) intensity parameters and found that the trend follows Ω2> Ω4> Ω6. The ionic nature of RE3+-O were evaluated by using bonding parameter (δ) value for C2 and D glass and found to be -0.0076 and -0.0102. Radiative properties were subsequently estimated using JO parameters and investigated radiative transition probabilities (AR), stimulated emission cross section (σR) and branching ratio (βR). The photoluminescence and radio luminescence spectra exhibit two prominent emission peaks at 484 (blue) and 575 nm (yellow) that corresponds to the4F9/2→6H15/2 and4F9/2→6H13/2 transitions respectively. The chromaticity coordinates were evaluated and found that these coordinates positioned in the white region with (x, y) = (0.348 0.382) and (0.325, 0.353) values for C2 and D glasses. The florescence decay from the 4F9/2 level was measure by monitoring the intense 4F9/2 to 6H9/2 transition. The decay time is found to be bi-exponential when monitored at λexi=387nm. The results obtained in present work demonstrate that the present glasses could be potential candidate for use in white light solid state lighting applications.
Key words: Judd-Ofelt theory, Photoluminescence, X-Ray luminescence, XAS spectra, EXAFS analysis.
1. Introduction Glass is material which provides enough room to investigate with their multi-functional characteristics behavior when doped with rare-earth oxides. Next generation is emerging from Light-emitting diodes (LEDs) as one of the solid-state lighting (SSL) devices which have shown potential for the replacement of its conventional counterpart such as incandescent light bulbs and fluorescent lamps. Judd-Ofelt intensity parameters, Ωλ (λ = 2, 4 and 6), some important dynamic parameters such as radiative transition rates, oscillator strengths, fluorescence lifetimes, fluorescence branching ratios and quantum efficiencies can be confirmed. Judd-Ofelt calculation, some fundamentals should be strictly assured: a) the electron in all the excited state levels can be quickly relaxed to the emitting level, in this sense it is possible to obtain an excitation spectrum having the same spectral line shape with the absorption spectrum; b) the obtained excitation spectrum should be intensity-calibrated to remove the deviation in spectral line shape from the absorption spectrum induced by the different detector and instrument responses (Zhang et al., 2018). Also based on the semiconductor light emitting, laser diodes (LDs) have characteristics of monochromaticity, polarization and parallelism on beam quality due to coherent phase photon emission (Zang et al., 2017). Dysprosium being topic of interest in recent decade due to their intense blue and yellow emission originating from 4F9/2 to 6H15/2 and 6H13/2 respectively when excited by UV source (Khan et al., 2019c). The surroundings in the region of Dy3+ ion is strongly influencing the hypersensitive transition (4F9/2 to 6H13/2) leading to variation in their yellow to blue emission intensity ratio. Dy3+ ions emission spectrum consists of strong bands corresponding to the 4F9/2 → 6H15/2 (blue) and 4F9/2 → 6H13/2 (yellow) transitions accompanied by transition in the visible range. Numerous Dy3+-doped glass systems were investigated and studied for obtaining white light through appropriate combinations of these luminescent band intensities and two primarycolored luminescent materials especially Y/B variations (Shasmal and Karmakar, 2019). In this paper we focus on the two primary colored luminescent transitions to obtain pure white light. Introduction of Gd3+ ions acts as a sensitizer and enhances the luminescence intensity and also influences for energy transfer characteristics (Rajaramakrishna et al., 2020; Ravangvong et al., 2020). Many literatures show energy transfer phenomenon when co-doped with two or more
rare-earth ions (Zheng et al., 2011) and host itself in the form of charge transfer band (CTB) (Tian et al., 2013). Introduction of Ce3+ ions which were co-doped in gadolinium dysprosium alkaline earth borate glasses which affects photoluminescence emission and tailor their white luminous due to Y/B ratio from Dy3+ doped glasses under the appropriate excitation suggesting a promising and efficient optical devices for laser illumination as well as the color coordinates which are evaluated from CIE color coordinate diagram (Tian et al., 2013) and correlated color temperature (CCT) of white fluorescence to anticipate their cool warm temperature by the color due to the rare-earth.
2. Investigational procedure Glass fabrication Glasses with 10g batch as a starting raw material with high purity of 99.99% AR grade calcium carbonate (CaCO3), zinc oxide (ZnO), gadolinium tri-oxide (Gd2O3), orthoboric acid (H3BO3), dysprosium tri oxide (Dy2O3) and cerium fluoride (CeF3) were used to synthesis according to glass formula 20CaCO3-20ZnO-10Gd2O3-(50-x)B2O3-Xmol%Dy2O3 (X = 0.3 (C1 glass), 0.5 (C2 glass), 1.0 (C3 glass) mol%) and 20CaCO3-20ZnO-10Gd2O3-49B2O3-0.5Dy2O3-0.5CeF3 (D glass) using muffle furnace. The samples were polished into 10mm×5mm×3mm thickness. Absorption and photoluminescence studies were performed for the prepared samples. The chemical composition and sample codes are presented in Table 1. Characterization Techniques Refractive index was calculated using Abbe refractometer (ATAGO) with sodium vapor lamp (598.3 nm (D line)) as mono bromo naphthalene being contact liquid. UV-Vis-NIR spectrometer (Shimadzu, UV-3100) was used to determine the absorption spectra ranging from 2200 nm to 200 nm wavelength. Photoluminescence and lifetime decay analysis of the prepared samples were measured Cary Eclipse fluorescence spectrometer (Agilent technologies Inc). X-ray induced luminescence were measured by using X-ray generator with 50kv voltage and 30mA current at room temperature. Synchrotron studies were carried in SLRI (Synchrotron Light Research Institute Thailand). 3. Physical Properties
Density of the prepared samples were measured by applying Archimedes principle which were obtained using the relation (Rajaramakrishna et al., 2014). From Table.2 the density of the glass increases with increase in Dy3+ concentration due to higher molecular weight of the Dy3+ ion which replaces Boron atom in the glass matrix as well as Dy3+ ion concentration also increases with increase in the Dy2O3. Whereas density increases with co-doping of Dy3+ + Ce3+ and molar volume decreases suggesting that they yield rigidity or structure compactness in the glass matrix. It is observed from Table 2 that decrease in polaron radius (rp) from 0.999 nm to 0.669 nm with increase in concentration of Dy3+ ions which is ascribed to yield rigidity in structure or tighten around Dy3+ ion inside host matrix. When co-doped with Dy3+ + Ce3+ ions they show similar trend. Such compactness of the structure could affect the luminescence intensity of the glass. 4. Analysis of absorption spectra The absorption studies of 20CaCO3-20ZnO-10Gd2O3-(50-x) B2O3 glasses doped with various concentration of Dy2O3 are calculated in UV-Vis and NIR region are shown in Fig.1. The spectra consists of ten absorption peaks position at 384, 425, 452, 472, 750, 801, 900, 1088, 1269 and 1678 nm originating from lower level of 6H15/2 to the higher level of 4I(3)13/2, 4G(4)11/2, 4I(3)15/2, 4
F(3)9/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2,6F11/2 and 6H11/2 for Dy3+ ion. With increasing concentration of
Dy2O3 content the absorption intensity of all the transition increases. For Dy3+ ions 6F11/2 have highest intensity and is found to be hypersensitive(Khan et al., 2019b; Shasmal and Karmakar, 2019; Zang et al., 2017). Table 3 shows JO parameters for C2 and D glass and are found to be Ω2=1.1035, Ω4=0.3430, Ω6=0.4663 and Ω2=1.0398, Ω4=0.3009, Ω6=0.5265 (x 10-20 cm2) respectively. The JO parameters follow Ω2 > Ω6 > Ω4 showing elevated values than other reported as shown in table.4 and follows the same fashion compared with other literatures PBZLBD (Zulfiqar Ali Ahamed et al., 2013) LPABD (Deopa and Rao, 2017) PTBD (Vijaya Kumar et al., 2012) PBAWD (Pisarska, 2009) ZNBBD1 (Hegde et al., 2019) BiZNBD (Shanmugavelu and Kumar, 2014) LFBPD (Balakrishna et al., 2012). 4.1 Judd-Ofelt parameters and Radiative properties The experimental oscillator strength (fexp) were studied from absorption spectrum by using the following formula (Judd, 1962; Ofelt, 1962). Judd-Ofelt Ωλ (λ =2, 4, 6) is the intensity parameter were obtained using reported literature (Balakrishna et al., 2012; Deopa and Rao, 2017; Hegde et
al., 2019; Pisarska, 2009; Rajaramakrishna et al., 2014; Shanmugavelu and Kumar, 2014; Zulfiqar Ali Ahamed et al., 2013). The Ωλ parameters have been derived from the electric-dipole contribution of the experimental oscillator strengths using a least square fitting approach (Khan et al., 2019a, 2018; Kirdsiri et al., 2019, 2018; Shoaib et al., 2019b, 2019a). JO- intensity parameters are used to determine the radiative properties such as transition probability (AR), branching ratio
, stimulated emission cross section (σ(λp)).
4.2. Nephelauxetic effect In lanthanides the f-shell being partially half filled due to their covalent character of the rareearth oxygen bonding which can be determined by nephelauxetic effect. Nephelauxetic ratio (β) is used to determine the nature of Dy3+ ligand bond using the relation (C.K. Jorgensen, 1962, SINHA, 1966). =
(1)
Where υa and υc is the wave number (cm-1) of particular corresponding transition of rare earth ion in the aqua-ion (Carnall et al., 1968) and in the title glass respectively. Bonding parameter (δ) is calculated from the average value of β by =
(
)
(2)
The δ value for C2 and D glass is found to be -0.0076 and -0.0102 which indicate the ionic nature of RE3+-O bonding due to their negative value and found that D glass shows more ionic than C2 glass. The available NBO's could open up the network wide to form Ln3+- O more ionicity in D glass as compared to C2 glass, the ionicity could be due to the oxygen vacancy near Ln3+-O which is confirmed with XAS results discussed in section.8. Since this is confirmed from the JO intensity Ω2 parameter where D glass show less value than C2 glass suggesting the asymmetry of the Dy3+ ions (Rajaramakrishna et al., 2014). It is clear that in the present glasses the covalency asymmetry around the Dy ions is altered by their neighboring counterpart such as Gd3+ ions or Ce3+ ions. From Table 3 it can be seen that stimulated emission cross section σ (λP) is found to be higher as compared to other reported literature, 5. Photoluminescence Excitation spectra (λemi = 575 nm):
The excitation spectra of C2 and D glass shown in Fig.2 was monitored at 575 nm Dy3+ emission wavelength. These glasses show prominent signature excitation peaks of corresponding rareearth ions and also charge transfer bands at 200-225 nm. In C2 glass it was observed 10 prominent peaks in which 2 peaks corresponding to Gd3+ ions at 254 nm (8S7/2→6DJ) and 275 nm (8S7/2→6I11/2). Remaining 8 peaks corresponding to Dy3+ ions 312, 325, 351, 365, 387, 426, 452 and 473 nm from ground state 6H15/2 →6P3/2+4M11/2, 4I9/2, 6P7/2, 4I11/2+6P5/2, 4I13/2+6F7/2, 4G11/2, 4
I15/2, 4F9/2 respectively. Whereas in D glass sample a prominent broad excitation peak was
observed at 315 nm corresponding to Ce3+ via parity allowed 4f (2F5/2) →5d absorption. 6. Photoluminescence Emission spectra of Dy3+ (λexi = 387 nm): The Fig.3 exhibits the PL emission spectra of C series and D glasses. All the glass samples were excited with 387 nm in the spectral range of 400 nm to 700 nm. The spectra exhibit three prominent emission peaks at 484 (blue), 575 nm (yellow) and 665 nm (red) that corresponds to the4F9/2→6H15/2,
4
F9/2→6H13/2 and
4
F9/2→6H11/2 transitions respectively as
displayed in Fig.4. In addition, transition located at 665 (red) attributed to 4F9/2→6H11/2 (Khan et al., 2019c; Shasmal and Karmakar, 2019; Zang et al., 2017). Radiative properties for fluorescent levels, 6H15/2, 6H13/2 and 6H11/2 of Dy3+ glasses have been estimated and presented in table 4. By substituting the known values of Sed and Smd radiative transition probabilities (AR) and in turn total radiative transition probability (AT), radiative lifetimes (τrad), branching ratios (βr) and absorption cross-sections for stimulated emission (σ(λp)) have been calculated 6H15/2, 6H13/2 and 6
H11/2 of Dy3+ ions. From Table 4 it can be seen that stimulated emission cross section σ (λP) is
found to be higher as compared to other reported literature (Hegde et al., 2019; Khan et al., 2019b; Ravangvong et al., 2019; Shanmugavelu and Kumar, 2014; Vijaya Kumar et al., 2012; Zulfiqar Ali Ahamed et al., 2013). Concentration quenching is observed at 0.5 mol% Dy3+ content, this is due to opening of cross relaxation channels (CRC) and resonance energy transfer (RET) in non-radiative transition as shown in Fig.4. The opening of cross-relaxation channels is the common process observed in the Dy3+ doped glasses where the excitation energy is transferred from one active Dy3+ ion in excited state (4F9/2) to the nearby ground state (6H15/2) Dy3+ ion which excites from the ground state to the intermediate state termed as CRC1, CRC2 and CRC3 which are as shown in the Fig.4 (Riseberg. L .A, 1977)(Dexter and Schulman, 1954; Zhong et al., 2008).
Electric dipole
transition is due to dependent of the local surroundings around Dy3+ ions and magnetic dipole transition is due to independent to the local surroundings around Dy3+ ions (Ma et al., 2015; Yan and Huang, 2007). The radiative properties of C2 and D glasses were obtained and values are tabulated in Table 3. The likelihood to achieve enough stimulated emission from particular transition for lasing action could be explained with branching ratio which should exhibit larger than 0.5 value to consider for their potential use for lasing emission (Maruyama et al., 2009). The transition from 4
F9/2 state to 6H13/2 state has branching ratio value (βR) 0.70 for C2 glass sample and 0.69 for D
glass sample suggesting their potential use for laser emission, moreover the value well agrees with experimental and calculated branching ratio (βR) value show 0.50 for all transitions of C2 and D glass samples. The energy transfer rate (WET) was calculated and found to be 24.68 S-1 and 4.208S-1 for C2 and D glass respectively. The multi phonon relaxation rate (WMPR) is not considered due the difference of energy gap is ~10000 cm-1 between 4F9/2 to 6H11/2. From the energy transfer rate, it is clear that D glass show less energy transfer rate suggesting that more probability of the back transfer (BT1) process. The excitation energy (387 nm) of Dy3+ ion and emission energy (372 nm) of Ce3+ ions overlaps in the form of resonance energy transfer (RET). 4
F9/2 → 6H13/2 transition being highest compared to other transition and hence it signifies the
capability of the transition for laser action. 7. Photoluminescence Emission spectra of Ce3+ (λexi = 315 nm): In the present case rare earths such as Gd3+, Ce3+ and Dy3+ are especially suitable for energy transfer and back transfer phenomenon due to these Ln3+ ions provide narrow electronic levels to which absorption occurs and from which fluorescence is observed. Symbolically, energy transfer can be written as 2(S)→1(S)→1(A)→2(A) or S*+A→S+A* When the active donor Ln3+ ions de-excited from higher excited state of 2(S) to the lower lying ground state 1(S), the energy transfer occurs which is released to bring an activator Ln3+ ions from the lower lying ground state 1(A) to its higher excited state 2(A). Energy transfer phenomenon from donor (Ce3+) to acceptor (Dy3+) plays an important role in luminescence. It is important to get different regions of the visible spectrum in a matrix in which different activation ions can be structurally active for cation sites (Gedam et al., 2013). The Ce3+-related photoluminescence emission and excitation spectra obtained for sample D are shown in Fig. 5.
The excitation at 315 nm, exhibits broad 5d1 → 4f (2F5/2, 2F7/2) emission of Ce3+ ions centered at 372 nm and through radiative energy transfer (ET1) signature peaks of Dy3+ ions at 484 nm (4F9/2 → 6H15/2) and 575 nm (4F9/2 → 6H13/2) emission were observed. These glasses contain Gd2O3 content hence, the Ce3+ excitation and emission were shifted slightly (within ∼5-7 nm) from other reported literature (Rathaiah et al., 2019), possibly due to the change in structural lattice around Ce3+ ions which gets localized. 8. Photoluminescence Emission spectra of Gd3+ (λexi = 275 nm): From fig. 6(a-b) when monitored at 275 nm excitation the lodged charge transfer band (CT) energy is promoted by 205 nm to 6G7/2 level of Gd3+ ions (as shown in Fig.2) subsequently the Gd3+ emission occurs from 6G7/2→6P7/2 level at 15,948 cm−1 (627 nm) with stokes shift from excitation source energy. Obviously the higher excited 4f multiplets of Gd3+ in visible-ultraviolet range play an important role in the transfer characteristics process: (a) Gd3+ to Ce3+ in UV range and (b) Gd3+ to Dy3+ in Visible range. Transfer Characteristics:
Monitoring at 275 nm, the Gd3+ ions excite to 6IJ state and
then non radiatively depopulates to the 6P7/2 level. (a) The UV emission at 315 nm (Fig.6(a)) corresponding to 6P7/2 → 8S7/2 transition is observed in C2 and D glass respectively. The emission at 315 nm decreases with addition of CeF3 concentration. The broad emission peak at 372 nm were observed in D glass corresponding to 5d1 → 4f (2F5/2, 2F7/2) transition whereas, this peak was absent in C2 glass. Such emission is classic example of energy transfer phenomenon (ET2) from 6P7/2 to 5d1 level of Ce3+ ions as depicted in Fig.4. (b) The visible emission (Fig.6(b)) corresponding to Dy3+ ions at 484 nm (4F9/2 → 6H15/2), 575 nm (4F9/2 → 6H13/2) and 664 nm (4F9/2 → 6H11/2) transitions. The emission of Dy3+ ions were observed when monitored Gd3+ ions showing complete energy transfer phenomenon (ET3) as depicted in Fig.4. In fact, the exchange between Ce3+ ↔ Gd3+ energy transfer phenomenon is achievable at all Ce/Gd concentrations. However, when the concentration of Gd3+ ions are less (i.e., Gd < 20%), the ET from Gd3+ to Ce3+ is more effective, due to the overlap of the Gd3+ emission peak at 315 nm (6P7/2→8S7/2) with Ce3+ absorption at 315 nm (4f - 5d), resulting in the increase of the Ce3+ emission [28] and decrease in Dy3+ emission as observed from Fig.6(a-b).
9. Yellow to Blue (Y/B) emission intensity ratio: The value of Y/B ratio is determined from luminescence transition of 4F9/2 → 6H13/2 transition (575 nm) to 4F9/2 → 6H15/2 transition (482 nm) for different excitation wavelength as shown in Table 5. The radiative transition takes place from 4F9/2 giving rise to intense blue and yellow emission. These intense emission bands arise as the energy difference between the states lying above 4F9/2 (21000 cm-1) is minutely small, and there is large separation (~6000 cm-1) between 4F9/2 and the next lower state 6F1/2 as shown in Fig.4. In addition to this, high phonon energy of the present glass system is another important parameter for such intense visible emission. The value of Yellow to Blue (Y/B) ratio increases with increase in Dy2O3 content when monitored at 387nm, whereas it decreases with addition of CeF3 content. When compared to C2 and D sample the Y/B ratio for both these glasses decreases when monitored for 387 nm for Dy3+ ions and 275 nm for Gd3+ ions. The data were compared with other reported literature which shows higher than (Vijaya Kumar et al., 2012; Vijaya et al., 2013; Zulfiqar Ali Ahamed et al., 2013) and less than (Khan et al., 2019c ; Shanmugavelu and Kumar, 2014). The data suggests that C2 and D glass shows higher covalence around Dy3+ ions and Gd3+ ions respectively. While the Y/B ratio can also be influenced due to glass composition, rare earth ion concentration and excitation wavelength 10. Lifetime Analysis: The luminescent transition 4F9/2 state of Dy3+ ion is acquired by exciting at 387 nm and emission at 575 are obtained and presented in table.6. The decay curves were fitted to different exponential equations, and the best fit was observed for the bi-exponential equation for C2 and D glass samples. The biexponential fit indicates that the interaction between rare earth ions becomes prominent, and the energy transfer process takes place from an excited Dy3+ ion (donor) to an unexcited Dy3+ ion (acceptor) (Linganna et al., 2015). The intensity of the luminescence spectra is given by literature (Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, 2005) = =
+
+ exp −
exp − +
+ ! exp
! exp
−
"
− +
(13)
"
# exp
−
$
(14)
where, I and Io represent the luminescence intensities at time t and 0, τ1, τ2 and τ3 represents the two (equation 13) and three (equation 14) components of the lifetime, corresponding to the fast and slow lifetimes for exponential components, respectively; A1, A2 and A3 are fitting constant, and t is the time. The calculated values of the average decay time (tavg) is found to be biexponential (equation 13 and 15) 0.578ms and 0.567ms for C2 and D glass respectively. The value of average decay time has been determined by the following formula (Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, 2005): %&'( =
)
" *) " " "
%&'( =
)
" *) " *) " " " $ $
)
)
*)" "
*)" " *)$ $
(15) (16)
It can be observed that the average lifetime decreases with addition of CeF3 content, which indicates the existence of energy transfer process between donor and acceptor as explained in section 5, 6 and 7. Ce3+ lifetime was also calculated using three exponentials (equation 14 and 16) and found to be 10.21 ns. The experimental decay lifetime and quantum efficiency (η=τexp/τrad) of luminescent 4F9/2 level using reported literatures (Rasool et al., 2013; Srihari and Jayasankar, 2017; Vijaya et al., 2013). The quantum efficiency found to be 0.858 and 0.860 for C2 and D glass samples respectively for Dy3+ ions. The efficiency found to be higher than (Hegde et al., 2019; Shanmugavelu and Kumar, 2014; Zulfiqar Ali Ahamed et al., 2013) and less than (Ravangvong et al., 2019).
11. X-Ray luminescence spectra From the Fig.8(a), the X-ray induced emission spectra of C2 and D glasses were synthesized with same cylindrical shape (1cm diameter) as that of BGO crystal so that it can be compared and these glasses were irradiated with X-ray at 50 kV and 20 mA. From Fig.9, the excitation source was x-ray, the spectral results were nearly identical to those obtained from the photoluminescence. From the Fig. 9, strong blue (482 nm) and yellow (575 nm) peaks were observed. In addition, from Fig.8(b), the white light emission could now be directly observed by naked eyes in the dark chamber when illuminated with UV lamp, and hence suggested that the developed glass could have been utilized and proved large potential in X-ray detections. The
ultraviolet excitation can directly activate the active luminescent ions, while the X-ray excitation would activate the holes and electrons from the host (glass) matrix. With the X-ray excitations, the secondary electrons are readily created, and eventually excite, either indirectly or directly.
12. CIE chromaticity Diagram The Commission Internationale de l'Elcairage (CIE) chromaticity diagram for the synthesized glass samples are shown in Fig.10 when excited at 387nm. In particular, the C2 and D glass sample shows white light emission with CIE color coordinates (x=0.348, y=0.382) and (x=0.325, y=0.353) respectively, which are close to those of the standard white light (0.3333, 0.3333), indicating that the glass is suitable for white light emitting device applications. The uncertainty in the color coordinates when monitored at 387nm shows around ±1%. The superiority of light can be evaluated in terms of the correlated color temperature (CCT) (M.N.Khan, 2013). Depending upon application fair values of CCT which ranges from 3500-6500 K which is acceptable for commercial purpose. McCamy existential formula use the color coordinates to calculate CCT values for the prepared glass samples (McCamy, 1992). The CCT value for C2 and D glass were found in the range of 4986 K and 5812 K at +,-. = 387 nm respectively. These CCT values for studied glasses shows slightly greater than the standard warm (CCT = 4000 K) (Kaewkhao et al., 2016), but D glass coordinates almost center of the white region. 13. XANES Analysis The Gd LIII-edge white line XANES spectra, resulted from a 2p3/2 → 5d excitation is very intense, which makes this spectrum susceptible to absorption effects when collected in fluorescence mode (Hess et al., 2002; Materlik et al., 1983). Fig.11(a) shows the XANES spectra of Gd LIII-edge for C2 and D glass, indicating the absorption edge at 7249.8 eV. In Fig.11(b), the Dy LIII-edge white line XANES spectra of the C2 and D glasses were nearly identical, demonstrating the sharp absorption peak (white line) at 7795.7 eV. The white line intensity when monitored for Gd ion (7249.8 eV) shows increased intensity for C2 glass whereas decreases in the case of Dy ion (7795.7 eV). This spectral change shows that the near neighbor environment of Gd / Dy undergoes rearrangement: either increased atomic order and/or a
more ionic character of the Gd-O bond, implying that the average Gd-O bond length increases in C2 as compared to D glass samples due to the increase in its white line intensity as shown in table.7. Furthermore, the intensity of white line is inversely proportional to oxygen vacancy. Moreover, we collected XANES spectra of the Ce-LIII absorption edge as shown in Fig.11(c). Under electric field, the amplitude and integrated area of the prominent Ce-LIII peaks at ∼ 5728 eV (the “white line”) increases with time, reaches a maximum and then levels off. Compared to the XANES spectrum of the pure Gd2O3, Dy2O3 and CeF3 standard samples, the energy difference of the white line and edge positions were less than 0.4 eV. Therefore, the XANES data confirmed that the oxidation states of Gd, Dy and Ce ions in the C2 and D glass found to be +3. 14. EXAFS Analysis monitored for Gd3+ / Ce3+: EXAFS spectra of D glass samples were obtained to study more details in terms of interatomic distance, coordination number and disordered structure. EXAFS spectra were Fouriertransformed into R-space. EXAFS in R-space of C2 and D glass samples were presented in Fig 12 and Fig.13 when probed for Gd atom. Similarly, EXAFS in R-space for D glass sample were presented in Fig.14 when probed for Ce atom. To investigate their local structure, Artemis program was utilized for fitting the structure data to the experimental spectra. The fitting results of C2 and D glass sample were shown in table.7. Regarding C2 and D glass, several standard model structures were tested such as GdBO3 (Orthorhombic, Hexagonal, Trigonal), Gd2O3 (Monoclinic, Trigonal, Cubic, Tetragonal), CeF3 (Hexagonal, Trigonal) and Ce2O3 (Monoclinic, Trigonal). The best fit was obtained by using the structures of the standard database of Gd2O3 3 c1) and Ce2O3 (Cubic-la33). The (Cubic-la33), GdBO3 (Orthorhombic-Ama2), CeF3 (Trigonal-P3 corresponding R-factor were between 0.01-0.02, indicating high accuracy and reliability for EXAFS analysis. Table 7, shows atomic distances (R), coordination numbers (N), Debye-Waller factors (4 ! ), amplitude reduction (56! ) and R-factor of C2 and D glasses.
Here in the present work we observed oxygen coordination number for C2 and D glass to be 6 in number. There are 2 inequivalent oxygen species, 2 oxygens and 4 oxygens with radial distances of 2.293 and 2.425 Å for C2 glass. Whereas D glass showed the radial distances were 2.342 and 2.584 Å. For D glass the experimental spectrum can be best fit by using different
model structure. However, we observe slight expansion in Gd-O and Gd-Gd bond lengths. The inter-atomic distance between Gd-O (coordination 6) and Gd- Gd are significantly higher in C2 glass than compared with D glass. However, the greater values of σ2 in D glass signifies higher atomic displacement. Ce3+ ions present in D glass are found to be coordinated with 7 fluorides and 6 oxygen's in the first shell. The fit data are reported in Table 7. Altogether, the results confirm that the Gd-O or Gd-Gd distance is less in D glass than in C2 glass thus signifying their efficient energy transfer characteristics. Conclusions The investigation carried out reveals a strong PL emission of Dy3+ ions was observed at 484 nm and 575 nm corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ions, respectively in C2 and D glass samples when monitored at 387, 315 and 275 nm excitation. A broad PL emission of Ce3+ ions was observed at 372 nm in D glass corresponding to 5d1 → 4f (2F5/2, 2F7/2) transition when monitored at 315 and 275 nm excitation. An energy transfer phenomenon was observed from Ce3+ → Dy3+ ions. Also, a back-transfer phenomenon was observed from Dy3+ → Ce3+ ions when monitored at 387. A strong emission of Gd3+ ions were observed at 315 nm and weak emission at 627 nm corresponding to 6P7/2 → 8S7/2 and from 6
G7/2→6P7/2 transition respectively in C2 glass but these peaks were less intense in D glass. The
quantum efficiency was obtained and found to be 0.858 and 0.860 for C2 and D glass samples respectively for Dy3+ ions. X-ray luminescence shows strong blue (482 nm) and yellow (575 nm) peaks and exhibits intense white light when illuminated with UV lamp. The CCT value were evaluated for C2 and D glass were found in the range of 4986 K and 5812 K at +,-. = 387 nm respectively. XANES spectra of Gd LIII-edge, Dy LIII-edge and Ce LIII-edge for C2 and D glass showed absorption edge at 7249.8 eV, 7795.7 eV and ∼ 5728 eV suggesting that these glasses shows +3 oxidation state. EXAFS analysis shows that the inter-atomic distance between Gd-O and Gd-Gd are significantly longer in C2 glass when compared with D glass supporting their efficient energy transfer and back transfer mechanism. Ce3+ ions in D glass are coordinated with 4 fluorides and 6 oxygen's in the first shell.
Acknowledgment
Author (R. Rajaramakrishna) would express deep gratitude to supervisor Dr. Jakrapong Kaewkhao. The authors would also like to express gratitude to Nakhon Pathom Rajabhat University and National Research Council of Thailand (NRCT) for financial supports of this work. This research was partially supported by Chiang Mai University.
References Balakrishna, A., Rajesh, D., Ratnakaram, Y.C., 2012. Structural and photoluminescence properties of Dy3 doped different modifier oxide-based lithium borate glasses. J. Lumin. 132, 2984–2991. https://doi.org/10.1016/j.jlumin.2012.06.014 Carnall, W.T., Fields, P.R., Rajnak, K., 1968. Electronic Energy Levels in the Trivalent Lanthanide Aquo Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+ 4424. https://doi.org/10.1063/1.1669893 Deopa, N., Rao, A.S., 2017. Photoluminescence and energy transfer studies of Dy3+ ions doped lithium lead alumino borate glasses for w-LED and laser applications. J. Lumin. 192, 832– 841. https://doi.org/10.1016/j.jlumin.2017.07.052 Dexter, D.L., Schulman, J.H., 1954. Theory of concentration quenching in inorganic phosphors. J. Chem. Phys. 22, 1063–1070. https://doi.org/10.1063/1.1740265 Gedam, S.C., Dhoble, S.J., Park, K., 2013. Resonant energy transfer from Ce 3+ →Dy 3+ and Mn 2+ in NaZnSO 4 Cl chlorosulphate phosphor. J. Lumin. 139, 47–51. https://doi.org/10.1016/j.jlumin.2013.02.010 Hegde, V., Chauhan, N., Viswanath, C.S.D., Kumar, V., Mahato, K.K., Kamath, S.D., 2019. Photoemission and thermoluminescence characteristics of Dy 3+ -doped zinc sodium bismuth borate glasses. Solid State Sci. 89, 130–138. https://doi.org/10.1016/j.solidstatesciences.2019.01.002 Hess, N.J., Begg, B.D., Conradson, S.D., McCready, D.E., Gassman, P.L., Weber, W.J., 2002. Spectroscopic investigations of the structural phase transition in Gd2(Ti1-yZry)2O7 pyrochlores. J. Phys. Chem. B 106, 4663–4677. https://doi.org/10.1021/jp014285t Judd, B.R., 1962. Optical Absorption Intensities of Rare-Earth Ions. Phys. Rev. 127, 750–761. Kaewkhao, J., Wantana, N., Kaewjaeng, S., Kothan, S., Kim, H.J., 2016. scintillating glasses. J. RARE EARTHS 34, 583–589. https://doi.org/10.1016/S1002-0721(16)60065-0 Kai Li, Xiaoming Liu, Yang Zhang, Xuejiao Li, Hongzhou Lian, J.L., 2005. Luminescence and energy transfer of Eu- and Mn-coactivated CaAl 2Si2O8 as a potential phosphor for whitelight UVLED. Chem. Mater. 17, 3883–3888. https://doi.org/10.1021/cm050638f Khan, I., Rooh, G., Rajaramakrishna, R., Sirsittapokakun, N., Kim, H.J., Kaewkhao, J., Kirdsiri,
K., 2019a. Energy transfer phenomenon of Gd 3+ to excited ground state of Eu 3+ ions in Li 2 O-BaO-Gd 2 O 3 -SiO 2 -Eu 2 O 3 glasses. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 210, 21–29. https://doi.org/10.1016/j.saa.2018.11.008 Khan, I., Rooh, G., Rajaramakrishna, R., Sirsittipokakun, N., Kim, H.J., Wongdeeying, C., Kaewkhao, J., 2018a. Development of Eu3+ doped Li2O-BaO-GdF3-SiO2 oxyfluoride glass for efficient energy transfer from Gd3+ to Eu3+ in red emission solid state device application. J. Lumin. 203, 515–524. https://doi.org/10.1016/j.jlumin.2018.07.009 Khan, I., Rooh, G., Rajaramakrishna, R., Srisittipokakun, N., Kim, H.J., Kaewkhao, J., Ruangtaweep, Y., 2019b. Photoluminescence Properties of Dy3+ Ion-Doped Li2O-PbOGd2O3-SiO2 Glasses for White Light Application. Brazilian J. Phys. https://doi.org/10.1007/s13538-019-00695-0 Khan, I., Rooh, G., Rajaramakrishna, R., Srisittipokakun, N., Wongdeeying, C., Kiwsakunkran, N., Wantana, N., Kim, H.J., Kaewkhao, J., Tuscharoen, S., 2019c. Photoluminescence and white light generation of Dy 2 O 3 doped Li 2 O-BaO-Gd 2 O 3 - SiO 2 for white light LED. J. Alloys Compd. 774, 244–254. https://doi.org/10.1016/j.jallcom.2018.09.156 Kirdsiri, K., Raja Ramakrishna, R., Damdee, B., Kim, H.J., Kaewjaeng, S., Kothan, S., Kaewkhao, J., 2018. Investigations of optical and luminescence features of Sm3+ doped Li2O-MO-B2O3 (M =Mg/Ca/Sr/Ba) glasses mixed with different modifier oxides as an orange light emitting phosphor for WLED’s. J. Alloys Compd. 749, 197–204. https://doi.org/10.1016/j.jallcom.2018.03.266 Kirdsiri, K., Rajaramakrishna, R., Damdee, B., Kim, H.J., Nuntawong, N., Horphathum, M., Kaewkhao, J., 2019. Influence of alkaline earth oxides on Eu 3+ doped lithium borate glasses for photonic, laser and radiation detection material applications. Solid State Sci. 89, 57–66. https://doi.org/10.1016/j.solidstatesciences.2018.12.019 Linganna, K., Sreedhar, V.B., Jayasankar, C.K., 2015. Luminescence properties of Tb3+ ions in zinc fluorophosphate glasses for green laser applications. Mater. Res. Bull. 67, 196–200. https://doi.org/10.1016/j.materresbull.2015.02.062 Ma, Q.L., Zhai, B.G., Huang, Y.M., 2015. Effect of sol-gel combustion temperature on the luminescent properties of trivalent Dy doped SrAl2O4. Ceram. Int. 41, 5830–5835. https://doi.org/10.1016/j.ceramint.2015.01.012 Maruyama, N., Honma, T., Komatsu, T., 2009. Enhanced quantum yield of yellow photoluminescence of Dy3+ ions in nonlinear optical Ba2TiSi2O8 nanocrystals formed in glass. J. Solid State Chem. 182, 246–252. https://doi.org/10.1016/j.jssc.2008.10.028 Materlik, G., Müller, J.E., Wilkins, J.W., 1983. L-edge absorption spectra of the rare earths: Assessment of the single-particle picture. Phys. Rev. Lett. 50, 267–270. https://doi.org/10.1103/PhysRevLett.50.267 McCamy, C.S., 1992. Correlated color temperature as an explicit function of chromaticity coordinates. Color Res. Appl. 17, 142–144. https://doi.org/10.1002/col.5080170211
Ofelt, G.S., 1962. Intensities of Crystal Spectra of Rare‐Earth Ions, The Journal of Chemical Physics. https://doi.org/10.1063/1.1701366 Pisarska, J., 2009. Optical properties of lead borate glasses containing Dy3+ ions. J. Phys. Condens. Matter 21. https://doi.org/10.1088/0953-8984/21/28/285101 Rajaramakrishna, R., Knorr, B., Dierolf, V., Anavekar, R. V, Jain, H., 2014. Spectroscopic properties of Sm 3 þ -doped lanthanum borogermanate glass. J. Lumin. 156, 192–198. https://doi.org/10.1016/j.jlumin.2014.07.021 Rajaramakrishna, R., Nijapai, P., Kidkhunthod, P., Kim, H.J., Kaewkhao, J., Ruangtaweep, Y., 2020. Molecular dynamics simulation and luminescence properties of Eu 3 þ doped molybdenum gadolinium borate glasses for red emission. J. Alloys Compd. 813, 151914. https://doi.org/10.1016/j.jallcom.2019.151914 Rasool, S.N., Rama Moorthy, L., Jayasankar, C.K., 2013. Optical and luminescence properties of Dy 3+ ions in phosphate based glasses. Solid State Sci. 22, 82–90. https://doi.org/10.1016/j.solidstatesciences.2013.05.013 Rathaiah, M., Kucera, M., Pejchal, J., Beitlerova, A., Kucerkova, R., Nikl, M., 2019. Epitaxial growth, photoluminescence and scintillation properties of Gd3+ co-doped YAlO3:Ce3+ films. Radiat. Meas. 121, 86–90. https://doi.org/10.1016/j.radmeas.2018.12.013 Ravangvong, S., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Kaewkhao, J., 2020. Effect of sodium oxide and sodium fluoride in gadolinium phosphate glasses doped with Eu2O3 content. J. Lumin. 116950. https://doi.org/10.1016/j.jlumin.2019.116950 Ravangvong, S., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Sangwaranatee, N., Kaewkhao, J., 2019. Dy3+ ions doped (Na2O/NaF)-Gd2O3–P2O5 glasses for solid state lighting material applications. Solid State Sci. 97, 105972. https://doi.org/10.1016/j.solidstatesciences.2019.105972 Shanmugavelu, B., Kumar, V.V.R.K., 2014. Luminescence studies of Dy3+ doped bismuth zinc borate glasses. J. Lumin. 146, 358–363. https://doi.org/10.1016/j.jlumin.2013.10.018 Shasmal, N., Karmakar, B., 2019. White light-emitting Dy 3+ -doped transparent chloroborosilicate glass: synthesis and optical properties. J. Asian Ceram. Soc. 7, 42–52. https://doi.org/10.1080/21870764.2018.1555883 Shoaib, M., Rooh, G., Chanthima, N., Rajaramakrishna, R., Kim, H.J., Wongdeeying, C., Kaewkhao, J., 2019a. Intriguing energy transfer mechanism in oxide and oxy-fluoride phosphate glasses. Opt. Mater. (Amst). 88, 429–444. https://doi.org/10.1016/j.optmat.2018.11.059 Shoaib, M., Rooh, G., Rajaramakrishna, R., Chanthima, N., Kiwsakunkran, N., Kim, H.J., Kaewkhao, J., Tuscharoen, S., 2019b. Comparative study of Sm3+ ions doped phosphate based oxide and oxy-fluoride glasses for solid state lighting applications. J. Rare Earths 37, 374–382. https://doi.org/10.1016/j.jre.2018.09.008 SINHA, S.P., 1966. Complexes of the Rare Earths. Complexes Rare Earths 17–23.
https://doi.org/10.1016/b978-0-08-011616-7.50005-x Srihari, T., Jayasankar, C.K., 2017. Fluorescence properties and white light generation from Dy3+-doped niobium phosphate glasses. Opt. Mater. (Amst). 69, 87–95. https://doi.org/10.1016/j.optmat.2017.04.001 Tian, B., Chen, B., Tian, Y., Li, X., Zhang, J., Sun, J., Zhong, Haiyang, Cheng, L., Fu, S., Zhong, Hua, Wang, Y., Zhang, X., Xia, H., Hua, R., 2013. Excitation pathway and temperature dependent luminescence in color tunable Ba5Gd8Zn4O21:Eu3+ phosphors. J. Mater. Chem. C 1, 2338–2344. https://doi.org/10.1039/c3tc00915g Vijaya Kumar, M. V., Jamalaiah, B.C., Rama Gopal, K., Reddy, R.R., 2012. Optical absorption and fluorescence studies of Dy 3 -doped lead telluroborate glasses. J. Lumin. 132, 86–90. https://doi.org/10.1016/j.jlumin.2011.07.021 Vijaya, N., Upendra Kumar, K., Jayasankar, C.K., 2013. Dy3+-doped zinc fluorophosphate glasses for white luminescence applications. Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 113, 145–153. https://doi.org/10.1016/j.saa.2013.04.036 Yan, B., Huang, H., 2007. Sol-gel synthesis and luminescence of unexpected microrod crystalline Ca5La5(SiO4)3(PO4)3O2:Dy3+ phosphors employing different silicate sources. Opt. Mater. (Amst). 29, 1706–1709. https://doi.org/10.1016/j.optmat.2006.09.004 Zang, X.M.Z., Un, E.Y.B.P., In, H.L., 2017. Dy 3 + doped borate glasses for laser illumination 7, 4585–4591. Zhang, Y., Chen, B., Xu, S., Li, X., Zhang, J., Sun, J., Zhang, X., Xia, H., Hua, R., 2018. A universal approach for calculating the Judd-Ofelt parameters of RE3+ in powdered phosphors and its application for the β-NaYF4:Er3+/Yb3+ phosphor derived from autocombustion-assisted fluoridation. Phys. Chem. Chem. Phys. 20, 15876–15883. https://doi.org/10.1039/c8cp02317d Zheng, Y., Chen, B., Zhong, H., Sun, J., Cheng, L., Li, X., Zhang, J., Tian, Y., Lu, W., Wan, J., Yu, T., Huang, L., Yu, H., Lin, H., 2011. Optical transition, excitation state absorption, and energy transfer study of Er3+, Nd3+ single-doped, and Er3+/Nd 3+ codoped tellurite glasses for mid-infrared laser applications. J. Am. Ceram. Soc. 94, 1766–1772. https://doi.org/10.1111/j.1551-2916.2010.04323.x Zhong, J., Liang, H., Han, B., Tian, Z., Su, Q., Tao, Y., 2008. Intensive emission of Dy^3+ in NaGd(PO_3)_4 for Hg-free lamps application. Opt. Express 16, 7508. https://doi.org/10.1364/oe.16.007508 Zulfiqar Ali Ahamed, S., Madhukar Reddy, C., Deva Prasad Raju, B., 2013. Structural, thermal and optical investigations of Dy3+ ions doped lead containing lithium fluoroborate glasses for simulation of white light. Opt. Mater. (Amst). 35, 1385–1394. https://doi.org/10.1016/j.optmat.2013.02.006
Table.1. Sample code and compositions Main Code: Sample Code:
C
D
Compositions
C1
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.7B2O3 - 0.3Dy2O3
C2
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.5B2O3 - 0.5Dy2O3
C3
20CaCO3 - 20 ZnO - 10Gd2O3 - 49.0B2O3 - 1.0Dy2O3 20CaCO3 - 20 ZnO - 10Gd2O3 - 49B2O3 - 0.5Dy2O3 - 0.5CeF3
Table.2 Physical Properties of Dy3+ doped glasses Dy3+
Dy3+ / Ce3+
Physical Property 0.3
0.5
1.0
0.5 / 0.5
Density, ρ (g/cm3)
3.7804 3.8171 3.8632
3.8423
Molar Volume
26.309 26.215 26.294
26.209
Refractive index, nd ( =589.3 nm)
1.6546 1.6543 1.6541
1.6540
Dy3+-ion concentration (N ×1020ions/cm3) 0.6867 1.1487 2.2905
1.1490
Polaron Radius (rp) (×10-9 m)
0.9992 0.8419 0.6690
0.8418
Inter-atomic Radius (ri) (A˚)
2.4456 2.0602 1.6369
2.0601
Field Strength (×1016)
3.370
7.516
4.747
Dielectric Constant (ε)
2.7377 2.7367 2.7360
2.7357
Molar Polarizability (RM)
9.6499 9.6117 9.6386
9.6060
1.2748 7.6185 3.8199
7.6141
Electronic Polarizability (
)
4.747
Table.3. Judd-Ofelt parameters, experimental (fexp x 10-6) and calculated (fcal x 10-6) oscillator strength for C2 and D glass sample. Wavelength Energy
C2 Glass
D Glass
(nm)
(cm-1)
I(3)13/2
384
26041
1.2028 1.5289
G(4)11/2
425
23529
0.5137 0.1344 0.4716 0.1194
4
452
22123
1.7900 0.9031
472
21186
2.2060 0.3423 0.9681 0.3773
Transition 4 4
I(3)15/2
4
F(3)9/2
fexp
fcal
fexp
fcal
-
-
-
-
6
F3/2
750
13333
2.4360 0.3889 1.5340 0.4390
6
F5/2
800
12500
3.6000 2.0575 3.1840 2.3228
6
F7/2
900
11111
3.5830 4.4550 4.0415 4.8959
6
F9/2
1088
9191
5.1590 5.0031 5.3640 5.1921
F11/2
1269
7880
12.610 12.596 12.240 12.259
H11/2
1678
5959
2.4420 2.5481 2.8950 2.7494
Ω2
1.1035
C2 Glass (×10-19 cm2)
Ω4
0.3430
∆rms = ± 0.990
Ω6
0.4663
β
1.0077
δ
-0.0076
Ω2
1.0398
Ω4
0.3009
Ω6
0.5265
β
1.0104
δ
-0.0102
6 6
D Glass (×10-19 cm2) ∆rms = ± 0.632
Table 4. Radiative properties of C2 and D glass. Level 4
4
λp
∆λeff
AR
σ (λp) (x 10-20 cm2)
βr Exp
Cal
F9/2 → C2 Glass 6
H15/2
482
16.29
440.31
1.1176
0.49
0.20
6
H13/2
575
16.44
1425.3
6.8296
0.50
0.70
6
H11/2
665
9.35
149.82
0.7212
0.01
0.06
F9/2 → D Glass 6
H15/2
482
16.39
489.11
0.5837
0.48
0.21
6
H13/2
575
18.91
1412.81
4.8265
0.50
0.69
6
H11/2
665
15.71
144.13
0.7894
0.01
0.06
AT of 4F9/2 : (C2glass =2015.4 ; Dglass =2046.0), τrad : (C2glass =0.496 ms ; Dglass =0.488 ms)
Table.5 Emission intensity ratio of C and D glass samples. Glass Y/B Ratio (λexi= 387 nm) Y/B Ratio (λexi= 315 nm) Y/B Ratio (λexi= 275 nm) Dy3+ ions
Ce3+ ions
Gd3+ ions
C1
1.069
-
-
C2
1.075
-
1.024
C3
1.078
-
-
D
1.055
0.921
0.924
Table.6 Lifetime of C2 and D glass samples λexi = 275 nm
λexi = 387 nm
λexi = 315 nm
λemi = 575 nm λemi = 575 nm
λemi = 370 nm
Two-exponential
Three-exponential
Wavelength
Samples C2 Glass
0.683 ms
0.578 ms
-
D Glass
0.557 ms
0.567 ms
10.21 ns
Table. 7 EXAFS fitting parameters of Gd3+, atomic distances (R), coordination numbers (N), Debye-Waller factors (
), amplitude reduction ( ) and R-factor of C2 and D glass.
Samples Paths C2
D
D
N
(
) R(Å)
Gd-O(1)
2
1.039 0.005
2.982
2.293
Gd-O(2)
4
1.039 0.010
2.982
2.425
Gd-Gd(1)
4
1.039 0.024
2.982
4.108
Gd-O(1)
4
0.8
0.002
4.9
2.342
Gd-O(2)
2
0.8
0.011
4.9
2.584
Gd-Gd(1)
4
0.8
0.016
4.9
3.755
Gd-F(1)
8
0.8
0.030
4.9
2.531
Gd-F(2)
6
0.8
0.032
4.9
2.923
Gd-Gd(2) 12
0.8
0.031
4.9
4.134
Ce-O(1)
6
1
0.024
-4.922
2.380
Ce-Ce(1)
6
1
0.011
-4.922
3.913
Ce-F(1)
2
1
0.004
-4.922
2.238
Ce-F(2)
3
1
0.002
-4.922
2.472
Ce-Ce(2)
6
1
0.017
-4.922
4.248
Ce-F(3)
2
1
0.003
-4.922
2.654
R-factor 0.019
0.010
0.011
Fig.1. Absorption spectra of C2 glass
Fig.2. Excitation spectra of Dy3+/Ce3+ doped glasses (Monitored at λemi=575nm)
Fig.3. Emission spectra of Dy3+/Ce3+ doped glasses (Monitored at λexi=387nm)
Fig.4. Complete Energy transfer process of Gd3+/Ce3+/Dy3+ ions in the present glass system.
Fig.5. Emission spectra of C2 and D glass (Monitored at λemi=372 nm and λexi=315 nm).
Fig.6. Emission spectra of Dy3+/Ce3+ doped glasses (Monitored at λexi=275nm) (a) UV range (b) Visible range
Fig.7. Lifetime spectra of C2 and D glass samples.
Fig.8 (a) Glasses used to record X-ray luminescence spectra (b) Glasses illuminated in UV lamp.
Fig.9. X-ray luminescence spectra of C2 and D glass samples.
Fig.10. CIE spectra of C2 and D glass samples.
(a)
(b)
(c)
Fig. 11. XANES spectra of C2 and D glass probing for (a) Gd3+ (b) Dy3+ (c) Ce3+
Figure. 12 EXAFS fitting spectra in R-space of C2 glass sample probed for Gd.
Figure. 13 EXAFS fitting spectra in R-space of D glass sample probed for Gd.
Fig.14. EXAFS fitting spectra in R-space of D glass sample probed for Ce.
Research Highlights 1. Photo-luminescence properties of Dy3+ / Ce3+ doped 20CaCO3-20ZnO-10Gd2O3-49B2O3 glasses were investigated. 2. Transfer characteristics of Gd3+ → Dy3+ and back transfer characteristics of Dy3+ → Ce3+ ions were analyzed. 3. Radioluminescence spectra were analyzed and found to be similar to that of photoluminescence. 4. XANES analysis were employed to understand the oxidation state of rare-earth ions embedded in the glasses. 5. EXAFS fitting was employed using artemis program and well fitted with the standard model to understand their coordination number.
Conflict of interest: None