Spectroscopic investigations on Dy3+ ions doped zinc lead alumino borate glasses for photonic device applications

Accepted Manuscript Spectroscopic investigations on Dy photonic device application

3+

ions doped zinc lead alumino borate glasses for

Nisha Deopa, Shubham Saini, Sumandeep Kaur, Aman Prasad, A.S. Rao PII:

S1002-0721(18)30149-2

DOI:

10.1016/j.jre.2018.04.013

Reference:

JRE 227

To appear in:

Journal of Rare Earths

Received Date: 22 February 2018 Revised Date:

30 March 2018

Accepted Date: 3 April 2018

Please cite this article as: Deopa N, Saini S, Kaur S, Prasad A, Rao AS, Spectroscopic investigations 3+ on Dy ions doped zinc lead alumino borate glasses for photonic device application, Journal of Rare Earths (2018), doi: 10.1016/j.jre.2018.04.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

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Spectroscopic investigations on Dy3+ions doped zinc lead alumino borate glasses for photonic device application Nisha Deopa, Shubham Saini, Sumandeep Kaur, Aman Prasad, A.S. Rao*

Department of Applied Physics, Delhi Technological University, Bawana Road, New Delhi-110 042, India. .

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Abstract This paper presents the structural, optical absorption, photoluminescence (PL) and decay spectral properties of Dy3+ions doped zinc lead alumino borate (ZPAB) glasses to elucidate their possible usage in photonic devices such as w-LEDs and lasers. A broad hump shown by the XRD spectrum recorded for an un-doped ZPAB glass confirms its non-crystalline nature. The Judd-Ofelt (J-O) intensity parameter evaluated from the measured oscillator strengths of the absorption spectral features were used to estimate various radiative parameters and also to understand the nature of bonding between Dy3+ ions and oxygen ligands. Under 350 nm excitation, the as-prepared glasses are exhibiting two emission bands 4F9/2→6H15/2 (blue), and4F9/2→6H13/2(yellow) at 483 and 575 nm, respectively. From the PL spectra, the Y/B ratio values, CIE chromaticity color coordinates and color correlated temperature (CCT) were evaluated. The experimental lifetimes measured from the decay profiles are decreasing with increase in Dy3+ ions concentration in these glasses which may be attributed to the crossrelaxation and non-radiative multiphonon relaxation process. Decay profiles observed for higher concentration were well fitted to Inokuti-Hirayama (I-H) model to understand the energy transfer process and subsequent decrease in experimental lifetimes. The higher values of radiative parameters, emission cross-sections, quantum efficiency, optical gain and gain band width suggest the suitability of 0.5 mol% of Dy3+ in these ZPAB glasses for the photonic device application. *Corresponding author: Prof. A.S.Rao,E-mail: [email protected], Tel: +91 85860 39007,Fax:+91 01127871023.

1. Introduction

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Keywords: Glasses; J-O parameters; Luminescence; Inokuti-Hirayama model; Energy transfer; Rare earths

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Solid state lighting (SSL) has received considerable attention recently in the field of luminescent technology due to its eco-friendly nature and ability to consume less energy. Apart from this, SSL based devices are playing significant role in the development of white LEDs and seeking immense research due to their long life span, high efficiency and less power consumption as compared to conventional incandescent bulbs and CFLs [1-5]. The aforementioned applications have encouraged researchers to develop luminescent technology that is highly color tunable as well as efficient. Nowadays, LEDs have been fabricated by taking a combination of blue/n-UV excitation chips and phosphor wavelength converter models [6-8]. Phosphors are usually encapsulated in an epoxy resin which is made up of a polymer material. The epoxy resin can get damaged at high temperature or high energy excitation sources. Hence rare earth (RE) doped glasses are best alternatives to phosphors as they are highly durable and exhibit enhanced luminescence. Since glasses can be produced in high volume having optical uniformity, they are mostly favored over crystalline host. Glasses doped with RE ions have attracted significant attention because they can be fabricated easily in several forms, have higher transparency, require a simple manufacture procedure and exhibit homogeneous light emission. Also, they are less susceptible to damage due to heat and have low production cost [9].

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Among all the glass formers available, B2O3 is one of the best glass formers because of its low melting point, high thermal stability, high mechanical and chemical strength with high solubility of RE ions [10,11]. However, B2O3 possesses high phonon energy (1300 cm–1) due to stretching vibrations of network forming oxides [12]. Such high phonon energies in turn enhance the nonradiative emissions and hampers the luminescence efficiency. Therefore, to reduce such redundant phonon energies, preferably a heavy metal oxide (HMO) such as PbO is added to the borate glasses [13]. Consequently, larger quantum efficiencies are expected due to smaller multiphonon decay rates and larger radiative transition probabilities. ZnO in any host glass is having special feature owing to its dual nature as glass former as well as network modifier. Glasses containing ZnO are thermally stable, sublime and appreciably covalent in character [14, 15]. Introduction of Al2O3 in a glass matrix makes the glass more resistant to moisture [16]. It is worthy to note that Al3+ ions within the lead alkali borate glass network provides high densification and chemical and mechanical strength. The glass transition temperature also increases due to Al3+ addition along with a decrease in the coefficient of thermal expansion [17].

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The structural as well as mechanical properties of zinc lead borate glasses were broadly studied by many researchers [18-20]. Quite recently, some of the researchers have studied the optical properties of RE ions doped borate, Zn-borate, Al-borate and Pb-borate glasses [21–23]. The fascinating optical results reported in the aforementioned papers encouraged us to study the optical and photoluminescence properties of Dy3+ doped lead borate glasses added with zinc and aluminium. The main goal of this work is to evolve chemically more stable RE doped glassy system ideally having less phonon energies and better suited for fabricating a solid state lighting device with relatively good Y/B ratio, emission cross-section, optical gain, gain band width and quantum efficiency.

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2. Experimental

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In recent years, glasses doped with RE ions have drawn much attention due to their potential applications in solid-state lasers, optical amplifiers and three-dimensional displays [24-26]. Dy3+ ion is mostly used as a lanthanide (RE) ion in glass matrix for generating white light. The visible luminescence of Dy3+ ion mainly consists of two intense bands in the blue (470–500 nm) and yellow (570–600 nm) wavelength regions. At a suitable yellow to blue intensity ratio, Dy3+ ions will emit white light and can find interesting applications in luminescent materials [2729].Pondering on the scientific patronages proffered by the ZnO, PbO, Al2O3 and B2O3 in the present work, we prepared a germane glassy system namely zinc lead alumino borate (ZPAB) glass doped with different concentrations of Dy3+ ions to understand its structural as well as luminescence properties.

2.1 Sample preparation

The samples in the quaternary glass series were synthesized via melt quenching technique with the following molar composition 15ZnO-5PbO-(20-x)Al2O3-60B2O3-xDy2O3, (where x is 0.1, 0.5, 1.0, 1.5 and 2.0 in mol% and these glasses are labeled as glass A to E, respectively). All the starting materials used in the present work are of analar grade in quality. The materials were mixed in an agate mortar and melted in a silica crucible at 1100 °C in an electrical furnace for 2 h. The melts were then quenched between two preheated brass plates to form the glass samples of uniform thickness. The as-prepared glasses were annealed for 1 h in an electrical furnace at 350 °C to remove thermal strains. The photograph of as-prepared glasses under day light excitation and under UV excitation can be seen from Fig. 1.

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The XRD spectrum for an un-doped glass was recorded by using an X-ray diffractometer (Bruker; Model D8 advance). The FT-IR spectral recordings were done by using Perkin Elmer's Frontier FT-IR spectrometer and the pellet was formed by mixing powdered form of an un-doped glass in KBr. The absorption spectra for all the as-prepared glasses were recorded by using a Perkin Elmer Tensor-27 UV-vis-NIR spectrophotometer with a spectral resolution of 0.1 nm. The PL spectra for the titled glasses were recorded using a Shimadzu RF-5310 PC Spectrofluorophotometer with a spectral resolution of 0.5 nm. The decay spectral recordings were done using an Edinburgh FLSP900 fluorescence spectrometer with a spectral resolution of 0.1 nm taking xenon lamp as an excitation source. Refractive indices of the titled glasses were measured via Brewster's angle method with ±0.01 accuracy by using He-Ne laser (650 nm line). The densities of the as-prepared glasses were measured by Archimedes method taking water as an immersion liquid with an accuracy ±0.01 gm/cm3. Refractive index and density of the as prepared glasses are given in Table 1. 3. Results and discussion

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3.1 XRD and FT-IR spectral analysis

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The amorphous nature of an un-doped glass was confirmed from Fig. 2 which shows a broad hump in the XRD spectrum. To determine the functional groups present in the host glass, the FTIR spectrum was recorded for an un-doped glass and is shown in Fig. 3. Six active infrared modes were observed i.e., 694, 1020, 1379, 2854, 2925 and 3432 cm–1. The broadband observed at 3432 cm–1 signifies the symmetric O–H stretching. This also shows that the molecular water is present in the host matrix. Organic impurities can be attributed to the band at 2854 cm–1. The band at 2925 cm–1 can be attributed to the presence of hydrogen bonding. A band at 694 cm–1 is observed due to bending of B–O–B linkages in the borate network. B-O bond stretching of tetrahedral BO4 unites can be linked to the band at 1020 cm–1. Likewise, the band at 1379 cm–1 can be ascribed to B–O bond stretching of trigonal BO3 units. Ortho-borate and pyro-borate groups along with meta-borate chains and rings fall under such category. All the FT-IR bands are assigned properly and well matched with the reported papers [13, 30–32].

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3.2Absorption spectra, oscillator strength and J-O intensity parameters analysis

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Fig. 4depicts the absorption spectrum of 0.5 mol% of Dy3+ doped ZPAB glass in the wavelength range of 350 to 1800nm. Fig. 4 consist of 11 peaks at 364, 387, 426, 453, 473, 754, 799, 899,1088, 1264 and 1679nm in UV, vis & NIR regions corresponding to the transitions 6 H15/2→4M17/2,6P7/2, 4I13/2 + 4F7/2, 4I15/2, 4F9/2, 6F3/2, 6F5/2, 6F7/2, 6F9/2 + 6H7/2,6F11/2+6H9/2and 6H11/2 respectively. All the band positions were assigned as per the results published by Carnall et al.[33]. The absorption spectra for the remaining glasses are quite similar in bands and band positions exceptvariation in intensity. It is observed that for low Dy3+ ions concentration the peak corresponding to transition from6H15/2→4I15/2 and 6F9/2 does not appear due to strong absorption of host lattice in this region. The peak at 1264 nm corresponding to the transition 6H15/2 → 6H9/2 + 6F11/2, is highly intense and sensitive to the environment. This peak is hypertensive in nature and obeys the selection rule | ∆S| = 0, | ∆L| ≤2, | ∆J| ≤ 2 [34]. Generally, the intensity of absorption bands is identified by oscillator strength values and correlated with Judd-Ofelt (J-O) theory to evaluate radiative properties of RE doped ZPAB glasses [35,36]. The experimental oscillator strength (fexp) for the observed peaks of the Dy3+ ions in ZPAB glasses were evaluated by taking integrated area of absorption bands using the following expression[35,36].

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(1)

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where, is the molar extinction coefficient at a wavenumber cm–1, while m and e are mass and charge of electron, respectively. N is the Avogadro number and c is speed of light. The J-O theory was applied to the fexp values for estimating J-O intensity parameters with the help of least square fit analysis. The important expression for evaluating calculated oscillator strengths (fcal) and root mean square deviations (δrms) were taken from the literature [37, 38]. The fexp, fcal along with δrms values are presented in Table 1. The small values of δrms indicate validity of J-O theory in evaluating J–O parameters.

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The J–O intensity parameters thus estimated using least square fitting analysis are tabulated in Table 2. According to J–O theory, the intensity parameter is having two terms that describes different range effect. (i) Short range effect such as covalency between the RE3+ ions and the oxygen ligands which contribute to the Ω2 intensity parameter. (ii) Long range effect such as viscosity and rigidity of the host matrix which contribute to the Ω4 and Ω6 intensity parameter. The Ω2 parameter has strong impact on the local environment around the RE ion site therefore it is highly influenced by the hypersensitive transition. The Ω2 parameter can also be used to examine the asymmetry of the local environment in which Dy3+ ions are situated. It is observed from Table 2 that the magnitude of Ω2, Ω4 and Ω6 enhances with increase in the intensity of hypersensitive transitions and vice versa. Among all the transitions, the hypersensitive transitions is having the highest intensity for glass B, i.e., 0.5 mol% of Dy3+ and the lowest intensity for glass E, i.e., 2.0 mol% of Dy3+ ions. This indicates that the Dy3+ ions are present atsites with higher symmetry of crystal field for glass B and at sites with lower symmetry of crystal field for glass E. The J–O intensity parameters are following the same trend (Ω2>Ω4>Ω6) for all the asprepared glasses and are also in good agreement with some reported glasses [39–41]. 3.3Photoluminescentand radiative properties analysis

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The PL excitation spectra have been recorded for all the Dy3+ doped ZPAB glasses under 483 nm emission wavelength. Fig. 5 shows one such excitation spectrum recorded for glass B (0.5 mol% of Dy3+ ions) from 300 to 500 nm. Because of the similarity in band positions the excitation spectra pertaining to the remaining glasses were not shown here. Various excitation bands were observed at 324, 336, 350, 365, 387, 428, 452, and 475 nm in all the glasses corresponding to levels excited from ground state 6H15/2 to several excited states (6P3/2 + 4M17/2), 4I9/2, 6P7/2, (4I11/2 + 6 P5/2), (4I13/2 + 4F7/2), 4G11/2, 4I15/2, and 4F9/2, respectively [42,43]. Among several excitation bands, the one at 350 nm is the most intense. Therefore, 350 nm excitation wavelength has been used to record the PL spectra for all the glass samples. Fig. 6 shows the emission spectra of Dy3+ ions in ZPAB glasses. As shown in Fig. 6, the emission spectra consists of two intense emission bands at 483 (blue) and 575 nm (yellow) assigned to 4F9/2→6H15/2and 4F9/2→6H13/2 transitions, respectively. The 4F9/2→6H15/2 transition is magnetic-dipole (MD) in nature and dominates the hypersensitive electric-dipole (ED) 4F9/2→6H13/2 transition. The ED transition gets highly affected by the environment around the Dy3+ ions in the host glass whereas the MD transition remains unaffected by the crystal field strength [44]. In present analysis, MD transition dominates ED transition, indicating Dy3+ ions have occupied high symmetry sites with an inversion centre. The PL spectra for all the glass samples show similar profile without any shifting in the emission bands. The PL spectra for all the synthesized glasses show rise in the emission intensity with increase in the dopant concentration from 0.1 mol% to 0.5 mol% and

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beyond concentration quenching was observed. As the Dy3+ ion concentration increases, the average distance between Dy3+ ions in glass decreases and this may enrich the possibility of energy transfer between RE ions through non-radiative energy transfer process [45]. The partial energy level diagram explaining excitation, emission and non-radiative transition can be seen from Fig. 7.The Dy3+ ions excited from ground state (6H15/2) to different excited states dropping down to 4F9/2 meta-stable state through non-radiative process and produces the required population inversion as shown in Fig. 7. From there the Dy3+ ions are exhibiting two radiative emissions one in blue (483 nm) and the other one in yellow (575 nm) region as shown in Fig. 7. The yellow to blue intensity (Y/B) ratio reveals the degree of covalency between Dy3+ ions and the surrounding ligands. It also reveals the symmetry around Dy3+ ions. The Y/B intensity ratio close to unity indicates white light emission. The Y/B ratio has been determined from the integrated intensity ratio of IED/IMD using emission spectra for different concentrations of Dy3+ ions. These values are found to be 0.68, 0.76, 0.74, 0.78, and 0.72 for glass A, B, C, D, and E, respectively. The Y/B values less than unity indicate less degree of covalency and higher symmetric environment around Dy3+ ions in the ZPAB glass system [46-52].

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The PL spectral data in conjunction with the J-O theory allows to evaluate various radiative parameters such as radiative transition probability (AR), luminescence branching ratio (βR), total transition probability (AT) and radiative lifetime (τR) using the suitable formulae available in the literature [53]. The values of all the aforementioned parameters are tabulated in Table 3. The stimulated emission cross-section (σse) is very essential parameter as it exhibits the rate of energy extraction from a given material and is useful in identifying the potential laser transition of Dy3+ ions in glasses. The stimulated emission cross-section can be evaluated by using the following equation [54].

(2)

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where, λP is emission peak wavelength, ∆λp is the line width of the transition. The values of σse along with emission peak wavelength (λP), experimental branching ratios (βexp), gain band width (σse × ∆λp) and optical gain parameter (σse × τR) for the as-prepared glasses are presented in Table 4. It is observed that, glass B shows maximum value of σse for both the transitions 4F9/2→6H13/2 and 4F9/2→6H15/2. Fig. 8 shows bar diagram of σse versus Dy3+ ions concentration in various different borate glass hosts. It is observed that glass B is having higher σse value than 1DZCTFB [55], LiPbAlB0.5Dy [4], Dy:KLTB [56], PKBAFD10 [57], LCZSFBDy [58], ZnAlBiBDy[60] and OFBDy1.0 glass systems [61]. It is well known that RE doped glassy material possesses better lasing potentiality if β ≥ 0.5. From Tables 3 and 4 it is observed that the relatively higher value of βR and βexp makes them promising candidates for lasing action via4F9/2→6H15/2 (483 nm) emission channel. RE doped glassy materials are said to be quite suitable for optical fiber amplification if the values of σse × ∆λp and σse × τR are relatively large. It is seen from Table 4 that σse, λP, ∆λP, βR, βexp, σse × ∆λp and σse × τR parameters are the highest for glass B for both the transition (4F9/2→6H13/2, 4F9/2→6H15/2) which makes it a potential candidate for solid state laser applications as well as optical fiber amplification.

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In order to ascertain white light emission from Dy3+ doped ZPAB glasses, the CIE chromaticity coordinates have been evaluated from emission spectra for all the as-synthesized glasses and are found to be (0.301, 0.337), (0.310, 0.358), (0.314, 0.362), (0.315, 0.364), and (0.316, 0.359) for A, B, C, D, and E glasses, respectively. The CIE coordinates for all the glass samples are in the vicinity of standard equal energy point (0.333, 0.333). Fig. 8 shows the CIE chromaticity coordinates for 0.5 mol% of Dy3+ ions in ZPAB glass (glass B). The correlated color temperature (CCT) has been evaluated by using McCamy’s equation [61]. The CCT values are found to be 7046, 6444, 6225, 6179, and 6188 K for A, B, C, D, and E glass, respectively, indicating cool white light emission. These results indicate that Dy3+ doped ZPAB glasses are quite suitable for generating white light under n-UV excitation and are aptly suitable for designing w-LEDS useful in outdoor illumination.

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3.5Decay spectral analysis

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The decay profiles plotted by using PL decay measurements recorded at room temperature for 483 nm emission under 350 nm excitation wavelength is shown in Fig9. The decay curves for all the glass samples show single exponential nature for lower concentration and non-exponential for higher concentration.The non-exponential behaviour is due to the efficient energy transfer between Dy3+-Dy3+ ions. The experimental lifetime for 4F9/2 level has been calculated and is presented in Table. 5. The decay time decreases with increase in Dy3+ concentration reveals the characteristic of concentration quenching. These results are also consistent with concentration dependent PL spectral study. It is observed that experimental lifetime values of 4F9/2 excited stateare less than radiative lifetimes. This discrepancy between τexp and τR occurs due to nonradiative relaxation. The quantum efficiency (η) can be evaluated by using the following expression. (3)

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The η(%) values are presented in Table 5 and it is observed that among all the glasses under investigation, glass B possesses the highest quantum efficiency around 79.6%. The non-radiative decay rates (WNR) can be estimated by using the following expression (4)

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The WNR values thus calculated are tabulated in Table 5. It can be seen that, the WNR values are lowest for glass B which is having highest quantum efficiency. Larger WNR rates found at higher Dy3+ concentrations are also responsible for concentration quenching. 3.6 Inokuti-Hiryama (I-H) model analysis The decay profiles of higher Dy3+ ion concentrations were well fitted to Inokuti-Hirayama (I-H) model [62] with S=6, which suggests that the nature of interaction between Dy3+-Dy3+(donoracceptor) ions is predominantly dipole-dipole in nature. According to I-H model, the decay intensity is given by (5)

ACCEPTED MANUSCRIPT Here, S is having different values from 6 (Γ(X)=1.77), 8 (Γ(X)=1.43) and 10 (Γ(X)=1.3) indicating dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions, respectively. The remaining symbols have their standard meaning as given in I-H model. The energy transfer parameter (Q) is evaluated by the following formula (6)

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here, N0 is concentration of acceptor ions, R0 is critical energy transfer distance and defined as the separation at which acceptor ions energy transfer rate is equal to the decay rate of donor ions. Fig. 10 shows the I-H fitted decay curves for higher Dy3+ ions in ZPAB glasses (glass C, glass D, and glass E) by taking S=6. The curves are well fitted with I-H model and confirms dipole-dipole interaction between Dy3+ ions. It is observed from Table 5 that R0 decreases while Q increases with increase in Dy3+ ion concentration. This clearly confirms that the energy transfer through dipole-dipole interaction is responsible for concentration quenching as well as non-exponential nature of the decay profiles in the titled glasses. 4. Conclusions

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In summary, Dy3+ ions doped ZPAB glasses were synthesized and characterized through structural, absorption, PL and decay measurements. The XRD spectrum recorded for un-doped glass confirms amorphous nature of the prepared material. The presence of various structural units were identified through FT-IR spectrum recorded for an un-doped glass. The Judd-Ofelt analysis applied for the absorption spectral features allows to evaluate various radiative properties for the as-prepared glasses. The PL spectra recorded under 350 nm excitation for the titled glasses exhibit two peaks at blue (483 nm) and yellow (575 nm) region corresponding to 4 F9/2→6H15/2 and 4F9/2→6H13/2 transitions, respectively. The decrease in experimental lifetimes of 4 F9/2 excited level with increase in Dy3+ ions concentration is attributed to the energy transfer process between Dy3+-Dy3+ through cross relaxation process. The I-H models applied to the decay profiles further confirm the dipole-dipole interaction between Dy3+ ions responsible for concentration quenching as well as decrease in experimental lifetime. The calculated CCT values for the as-prepared glasses are found to be quite suitable for the preparation of w-LEDs used in day light. From the evaluated branching ratios, emission cross-sections, quantum efficiency, optical gain, and gain band, it is confirmed that 0.5 mol% of Dy3+ ions doped ZPAB glasses are optimum for preparing solid state lasers and solid state lighting.

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Graphic abstract

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Figure captions

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The decay spectral profiles of 4F9/2→6H15/2 (483 nm) emission transition of Dy3+ ions in ZPAB glasses under 350 nm excitation.

Fig. 1. Photographs of ZPAB glass with different Dy3+ ions concentrations.

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Fig. 2. XRD spectrum of an un-doped ZPAB glass.

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Fig. 3. FT-IR spectrum of an un-doped ZPAB glass.

Fig. 4. Absorption spectrum of 0.5 mol% of Dy3+ ions in ZPAB glass (glass B).

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Fig. 5. Excitation spectrum of 0.5 mol% of Dy3+ ions in ZPAB glass (glass B) under 483 nm emission.

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Fig. 6. PL spectra of Dy3+ ions in ZPAB glasses under 350 nm excitation.

Fig. 7. Energy level diagram of Dy3+ ions in ZPAB glass.

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Fig.8. Bar diagram of stimulated emission cross-section for Dy3+ ions in different borate hosts.

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Fig. 9. CIE chromaticity coordinates 0.5 mol% of Dy3+ ions in ZPAB glass (glass B).

Fig.10. The decay spectral profiles of 4F9/2→6H15/2 (483 nm) emission transition of Dy3+ ions in ZPAB glasses under 350 nm excitation.

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Fig.11. I-H fitted curves of 4F9/2→6H15/2 (483 nm) emission transition of Dy3+ ions in ZPAB glasses (glass C, D and E) under 350 nm excitation.

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nd

1.85

Glass C fexp fcal 4.79 3.59 9.27 9.43 5.65 5.85 4.49 6.51 3.73 3.46 1.53 0.64 1.42 0.51 3.05 1.34 1.61 0.63 4.52 1.91 4.27 0.13 ±1.78

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Glass B fexp fcal 5.04 3.77 9.53 9.70 5.89 6.14 4.71 6.86 3.98 3.65 1.85 0.68 1.67 0.54 3.49 1.41 1.87 0.66 4.81 1.91 4.56 0.14 ±1.97

2.78

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d

Glass A fexp fcal 4.52 3.36 8.96 9.11 5.34 5.49 4.16 6.07 3.36 3.21 1.07 0.61 1.15 0.47 2.73 1.25 1.38 0.59 4.29 1.93 3.92 0.12 ±1.60

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Transitions from H15/2→ 6 H11/2 6 F11/2 +6H9/2 6 F9/2 +6H7/2 6 F7/2 6 F5/2 6 F3/2 4 F9/2 4 I15/2 4 I13/2 + 4F7/2 6 P7/2 4 M17/2 (×10–6) 6

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Table 1 Experimental (fexp ×10–6), calculated (fcal ×10–6) oscillator strengths, r.m.s deviation ( ×10–6), density (d) and refractive index (nd) for Dy3+ ions in ZPAB glasses. Glass D fexp fcal 4.62 3.52 9.21 9.36 5.60 5.80 4.52 6.40 3.75 3.39 1.43 0.64 1.51 0.50 3.23 1.31 1.65 0.62 4.58 2.08 4.24 0.13 ±1.77

Glass E fexp fcal 4.44 3.37 8.62 8.76 5.43 5.59 4.34 6.16 3.50 3.26 1.28 0.61 1.27 0.48 3.10 1.26 1.34 0.59 4.31 2.02 4.09 0.12 ±1.66

2.83

2.85

2.94

3.03

1.97

2.03

2.19

2.21

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Table. 2:

Glass system

Ω2

Ω4

Ω6

Trend

Glass A

6.10

0.68

4.60

Ω2>Ω6>Ω4

Glass B

5.71

0.60

4.48

Ω2>Ω6>Ω4

Glass C

5.40

0.55

4.35

Ω2>Ω6>Ω4

Glass D

5.01

0.59

3.91

Ω2>Ω6>Ω4

Glass E

4.43

0.55

3.58

Ω2>Ω6>Ω4

Present work

PYBDy10

7.75

2.31

2.70

Ω2>Ω6>Ω4

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D0LBE

5.319

0.54

1.54

Ω2>Ω6>Ω4

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D1LBE

6.45

2.02

3.87

Ω2>Ω6>Ω4

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LSG

19.08

1.88

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Judd-Ofelt parameters (Ωλ×10–20 cm2) of Dy3+ ions in ZPAB glasses along with the other reported values.

6.04

Ω2>Ω6>Ω4

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References present work

Present work Present work

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Present work

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Table. 3 Transition probability (AR) (s–1), luminescence branching ratio (βR), total transition probability (AT) (s–1) and radiative lifetime (τR) (µs) for the observed emission transitions of Dy3+ ions in ZPAB glasses. AR

βR

AT

τR

1542.43 877.46

0.4287 0.2445

3589.38

278

F9/2→6H15/2 F9/2→6H13/2

3241.79 1595.77

0.5914 0.2946

5494.78

182

4

F9/2→6H15/2 4 F9/2→6H13/2

2347.07 1190.49

0.4757 0.2524

4715.93

212

4

F9/2→6H15/2 4 F9/2→6H13/2

3071.39 1471.39

0.5839 0.2570

5262.28

190

4

3182.28 1538.79

0.5562 0.2531

5714.29

175

Transition Glass A 4

Glass B 4

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F9/2→6H15/2 F9/2→6H13/2

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4

Glass C

Glass D

Glass E F9/2→6H15/2 4 F9/2→6H13/2

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λp =483 nm βexp σse (×10–22) σse ×∆λp (× 10–28)

Glass B 4

0.57 19.4 27.3

Glass C

F9/2→6H15/2 (Blue) 0.59 0.58 30.8 24.5 44.2 34.4

5.44 0.46 16.9 30.5

5.61 5.19 6 F9/2→ H13/2 (Yellow) 0.48 0.47 23.4 19.0 42.8 34.3

σse ×τR (× 10–25)

4.70

4.25

4

Glass E

0.54 27.6 39.1

0.53 26.5 37.3

5.24

4.90

0.41 17.5 31.9

0.40 14.5 26.3

3.33

2.69

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σse ×τR (× 10–25) λp =572 nm βexp σse (× 10–22) σse ×∆λp (× 10–28)

Glass D

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Spectral parameters Glass A

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Table 4 Emission peak wavelength (λp) (nm), experimental branching ratios (βexp), stimulated emission cross-sections (σse) (cm2), gain band width (σse ×∆λp) (cm3) and optical gain parameter (σse ×τR) (cm2·s) for the emission transitions of Dy3+ ions in ZPAB glasses.

4.03

τexp/µs

η (%)

Q

R0

WNR

Glass A

189.2

68.0

----

----

1688

145.7

79.6.

----

----

1369

Glass B

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Name of sample

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Table. 5 Experimental lifetime (τexp), quantum efficiency (η), energy transfer parameter (Q), critical transfer distance (R0) (nm) and non-radiative decay rates (WNR) for 4F9/2 →6H15/2 transition of Dy3+ ions in ZPAB glasses.

Glass C

132.8

62.6

1.26

0.230

2813

Glass D

125.2

65.7

1.99

0.224

2724

Glass E

120.0

68.5

2.73

0.220

2928