Concentration dependent luminescence spectral investigation of Sm3+ doped Y2SiO5 nanophosphor

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

Contents lists available at ScienceDirect

Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol

Concentration dependent luminescence spectral investigation of Sm3+ doped Y2SiO5 nanophosphor K. Dhanalakshmia,b, A. Jagannatha Reddyc,⁎, D.L. Monikad, R. Hari Krishnae,⁎, L. Parashuramf a

Department of Physics, New Horizon college of Engineering, Bangalore 560 103, India Research and Development center, Bharathiar University, Coimbatore 641 046, India c Department of Physics, M. S. Ramaiah Institute of Technology, Bangalore 560 054, India d Department of Physics, S J B Institute of Technology, Bangalore 560 060, India e Department of Chemistry, M. S. Ramaiah Institute of Technology, Bangalore 560 054, India f Department of Chemistry, New Horizon college of Engineering, Bangalore 560 103, India b

A R T I C L E I N F O

A B S T R A C T

Keywords: Y2SiO5 Combustion synthesis Photoluminescence Thermoluminescence

Sm3+ doped Y2SiO5 was prepared by a simple solution combustion synthesis using (oxalyl dihydrazide) ODH as a fuel. The prepared material was well characterized by the PXRD, FTIR, UV–Vis and SEM. SEM data reveals highly aggregate mass with highly porous structure. Photoluminescence studies for the prepared material show four prominent peaks at 561, 571, 600 and 646 nm, when excited at the wavelength 405 nm. These transitions are attributed to the intra 4f orbital change over from 4G5/2 level to the 6HJ. In the present study, it was observed that the transition 4G5/2 → 6H7/2 is the most intense transition, which is a consequence of both electric and magnetic dipole transition. Thermoluminescence experiments on γ-irradiated samples in the dose range of 300–600 Gy are studied. The (TL) glow curves intensity greatly depends on the size of the nanoparticles, surface area and duration of γ-exposure which was evident from the experimental data. TL intensity parameters such as activation energy, frequency factor and order of kinetics were evaluated using Chen's peak shape method to analyze the TL characteristics of the phosphor.

1. Introduction In recent years inorganic nano-materials doped with rare earth ions have been particularly investigated for their unique luminescent properties [1–3]. Many researchers have also proved that the bulk and nanoscale materials show completely different optical and luminescent behavior [4,5]. Among many inorganic materials used for technological applications, silicate based materials have proved to be promising in various fields. It is evident from the literature that metal silicates are being used in many areas. In Thermoluminescence dosimetry for the detection of ionizing radiations, Tb3+ doped Mg2SiO4 was proved to be an efficient phosphor [6]. Gd2SiO5 doped with Ce3+ exhibits efficient light output and fast decay time and hence it is used as scintillation phosphors [7]. For the development of tri-color lamp phosphors, Zn2SiO4: Mn was used as green component. Zorenko et al. reported that Y2SiO5 shows enhanced luminescence output when doped with some transition metal and rare earth ions [8,9]. Yttrium silicate is a well-known host material for rare earth activators because of its high visible light transparency, high luminescence efficiency and chemical stability [8]. In recent years, yttrium silicate

⁎

phosphor doped with rare earth and transition metal is being given much importance due to its strong withstanding property against the degradation in chemical and thermal environment [8–11]. The electronic energy of the 4f compounds (RE ions) have become a subject of enduring interest as they are useful as a spectral probe to study the perturbation effects in a host lattice and they are not much affected by the crystal field due to their inner 4fn shell [12]. The spectroscopic investigations of the energy levels of Sm3+ ions doped in different hosts have been reported [13–14]. Among the various RE ions, trivalent Samarium (Sm3+) displays efficient radiative recombination channels, mainly observed in the red-orange visible spectral range with different excitation wavelengths [15]. The importance of samarium is due to its variable oscillation strengths in different hosts that results in excellent emissions in visible and near-infrared wavelength. Further, its 4G5/2 state exhibits higher quantum efficiency and shows different radiative emission channels. The yellow and reddish orange emissions of Sm3+ are highly desirable for various applications such as color display, medical diagnostics and undersea communications [16,17]. In the present research work, we report Sm3+ doped Y2SiO5 nanophosphors prepared by combustion route using ODH as a fuel and study

Corresponding authors. E-mail addresses: [email protected] (A. Jagannatha Reddy), [email protected], [email protected] (R. Hari Krishna).

http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.040 Received 23 February 2017; Received in revised form 25 May 2017; Accepted 26 May 2017 0022-3093/ © 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Dhanalakshmi, K., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.05.040

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

K. Dhanalakshmi et al.

2. Experimental

observed in the pattern, which indicates that the dopant Sm3+ ions are successfully incorporated into the host lattice. As per the Yixiu Luo et al. report [19], in monoclinic Y2SiO5 there are two sites of Y, one Si site and five O sites. Y occupies two nonequivalent sites with six or seven O atoms coordinated and form YO6 or YO7 polyhedral respectively. Therefore, the preferable site occupancy of Sm3+ can be calculated using an acceptable ionic difference (Dr) between doped and substituted ions taking co-ordination into account [20]. The value of Dr. between Sm3+ and Y3+ on six co-ordinated sites is − 6.4 while that between Sm3+ and Y3+ on seven co-ordinate sites is − 11.03. Obviously, it proves the doping of Sm3+ would clearly substitute the yttrium with six co-ordination site rather than seven co-ordination sites. The difference in ionic radii is evaluated based on the following formula.

2.1. Synthesis

Dr =

The raw materials, yttrium oxide (Y2O3; 99.99%, Sigma Aldrich Ltd.), fumed silica (SiO2; 99.99%, Merck Ltd.) and samarium oxide (Sm2O3; 99.99%, Sigma Aldrich Ltd.) are the sources of Y, Si and Sm respectively. Nitric acid (HNO3; Merck Ltd.) was used for conversion of oxide to nitrates. Oxalyl di hydrazide (ODH: C2H6N4O2) is used as the fuel. The stoichiometry of the redox mixture used for the combustion is calculated based on the total oxidizing and reducing valencies of the compounds [18]. Phosphors Y2 − xSmxSiO5 (x = 1, 3, 5, 7 and 9) mol% were prepared by solution combustion method. In the first step, stoichiometric quantities of Y2O3 and Sm2O3 are treated with ~10 ml of 1:1 HNO3 and the mixture was heated on a sand bath till the excess nitric acid was evaporated to convert the oxides into respective nitrates. To the resulting transparent nitrate solution, required amount of SiO2 and ODH was added followed by 20 ml of deionized water. The aqueous mixture was stirred using magnetic stirrer to get a homogeneous mixture. This was introduced into a pre heated muffle furnace maintained at ~ 500 °C. The mixture first underwent dehydration and auto ignited with flames on the surface, which quickly spreads in the entire volume forming a white fine voluminous product. This product is taken in alumina crucible and calcinated at 1300 °C for 3 h. A series of powders with various compositions of samarium was synthesized in the same manner.

where CN is the coordination number, Rh(CN) is the radius of host cations, and Rd(CN) is the radius of doped ion. No peaks corresponding to other crystalline phases within the PXRD limit are observed. The reduction of the FWHM as well as the increase of sharpness of the XRD peaks with Sm3+ incorporation indicates the increase in the crystallization of the Sm3+:Y2SiO5. It should be noted that the method followed for the synthesis is solution combustion synthesis. In this technique the exothermic reaction between oxidizer and fuel is used to produce the oxide materials. The exothermic reaction and the flame temperature generated depend on the nature of the fuel/ oxidizer. In the present case with increase in the Sm3+ concentration the increases in crystallinity may be due to the higher flame temperature produced when samarium nitrate is also used as oxidizer along with yttrium nitrate. Furthermore, the crystallite size is estimated for the powder from the full width half maximum (β) of the diffraction peaks, using DebyeScherer's method [21].

its photoluminescence (PL) and Thermoluminescence (TL) properties. Conventionally, solid state diffusion methods have been used for the synthesis of silicates. Another technique, sol-gel synthesis, has also been used which enables the preparation of fine and homogenous powders. But these methods have severe disadvantages such as inefficient diffusion resulting in inhomogeneous products, long reaction times and high energy consumption. However, solution combustion synthesis is a lowcost, time saving method and has been effectively used for the preparation of a variety of industrially important materials [18]. Therefore, we adopted combustion technique for preparation of sm3+ doped Y2SiO5 and detailed investigations of concentration dependent PL, J-O intensity parameters and TL studies are presented in this paper.

Rh (CN) − R d (CN) Rh (CN)

D = kλ βcosθ

(1)

(2)

In the above equation, ‘λ’ is the wavelength of X-ray (1.542 Å), ‘θ’ the Bragg angle, ‘k’ is the constant depends on the grain shape (0.94 for spherical). The estimated average crystallite size is found to be in the range of ~25–40 nm (for Sm3+ = 0 to 9 mol%).

2.2. Instruments

3.2. FT-IR analysis

Powder X-ray diffractometer (Shimadzu 7000 s, CuKα (1.541 Å) with a nickel filter was used to obtain the diffraction data. FTIR studies were performed on a Perkin Elmer spectrometer (Spectrum 1000) using KBr pellets. The morphology and structure of the samples were inspected using SEM (Hitachi). The absorption spectra of the samples were recorded on a SL-159 ELICO UV–Vis spectrophotometer. The photoluminescence (PL) measurements were performed on a Jobin Yvon spectrofluorometer (Fluorolog–3, HORIBA) equipped with a 450 W xenon lamp as the excitation source. TL measurements were carried out using Nucleonix TL reader. The Co-60 γ-ray was used as irradiation source in the dose range 300 Gy to 600 Gy.

The FT-IR spectra for undoped and doped (1 mol%, 5 mol%: Sm3+) Y2SiO5 are as shown in the Fig. 2. A prominent band at 564 cm− 1 for un-doped Y2SiO5 can be attributed to YeO stretching vibrations. This peak was observed to be broadened upon doping which is clearly indicated in the spectrum. In doping process, a small peak was observed at 533 cm− 1 which is due to the stretching vibrations of MeO bond indicating the existence of new metal-oxygen bonds. The bands > 800 cm− 1 are the characteristic of SieO [22,23]. It is observed from the spectra that no peaks of eOH due to water are observed. This is due to the fact that all the samples are calcined at 1300 °C for 3 h, which eliminates even the presence of lattice associated water.

3. Results and discussion

3.3. SEM and TEM images

3.1. Structural characterization

The SEM image of un-doped and 3 mol% Sm3+ doped Y2SiO5 are shown in Fig. 3 (a) and (b). The microstructure appears to be a highly porous and irregular structure which is expected of a combustion-synthesized product. This is due to evolution of large quantities of gases during synthesis. In order to further elucidate the nature of powder particles, the Y2SiO5:Sm3+ powders were characterized by TEM. Fig. 3 (c) and (d) shows the TEM image of the powder which shows agglomerated nanoparticles with sizes in the range of ~40–50 nm. The highly crystalline nature of particles is also evident from the selected

Phase purity of the Sm3+ doped Y2SiO5 samples were investigated by X-ray diffractometer. Fig. 1 shows the XRD patterns of prepared Y2SiO5:Sm3+ samples calcined at 1300 °C for 3 h. In the graph, the presence of sharp peak shows the crystalline nature of the prepared sample. Further, all the diffraction peaks are well matched to the monoclinic phase of Y2SiO5 with JCPDS number 36-1476. It can also be noted that no other phase and no shift in the peak position was 2

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

K. Dhanalakshmi et al.

Fig. 1. X-ray diffraction patterns of Y2SiO5:Smx3+ nanophosphor with the standard JCPDS: 36-1476.

Sm3+ doped Y2SiO5 powder. 3.4. UV–Vis absorption spectrum To study the optical property of the Sm3+ doped Y2SiO5 samples, UV–Visible absorption spectra were recorded as shown in Fig. 4. The appearance of broad band at 253 nm corresponds to charge transfer from valence band to conduction band [22]. Further, another two peaks at 405 nm and 474 nm start appearing with increasing Sm3+ concentration that corresponds to intra-configuration (f-f) transition from the ground state of Sm3+ ions to various excited states [Oj]. The intensity of this transition becomes significant as increasing doping concentration indicating the effect of Sm3+ concentration on the UV–Vis absorption. The optical energy gap of prepared sample was calculated using Eq. (4) [25].

(b)

M-O

Transmittance (%)

(c)

αhν~(hν − Eg ) n

O-H

(a)

4000

3500

Si-O

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 2. Fourier transform infrared spectra of Y2SiO5 (a) un-doped (b) 1 mol% Sm3+ and (c) 5 mol% Sm3+.

area of electron diffraction pattern (not shown here). The nature of crystalline phase of the Y2SiO5 powder was further studied by indexing the SAED pattern. Examinations at higher magnification (HRTEM) revealed crystalline nanoparticles with well-defined lattice fringes without any amorphous layer. This is further confirmed by crystallinity index (Icry) which is given by [24].

Icry

Dp (SEM, TEM ⎤ (I ≥ 1.00) =⎡ ⎢ Dcry (XRD) ⎥ cry ⎣ ⎦

(4)

where hν is the photon energy and α is the optical absorption coefficient near the fundamental absorption edge. The absorption coefficient α is calculated from these optical absorption spectra. The values of the optical band gap energy is obtained by plotting (αhν)n vs hν in the high absorption range followed by extrapolating the linear region of the plots to (αhν)n = 0. Eg is the optical band gap and n is the constant associated to the different types of electronic transitions. n = 1/2, 2, 3/ 2, 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions respectively [26]. The obtained Eg values are found to be in the range 5.52–5.67 eV which indicates that the allowed direct transition is responsible for the inter band transitions in undoped and doped samples. The range of Eg value represents the degree of structural order–disorder in the lattice, which is able to change the intermediary energy level distribution within the band gap [27]. 3.5. Photoluminescence (PL) studies The PL emission spectra of Y2SiO5:x Sm3+ (x = 0.01–0.11) phosphor upon 408 nm excitation is shown in Fig. 5. In the PL spectra, three prominent emission peaks are observed in the wavelength range 540–700 nm. These peaks are due to the intra 4f transitions from the 4 G5/2 level to the 6HJ (J = 5/2, 7/2 and 9/2). The characteristic emission peaks observed at 561, 571, 600 and 646 nm are ascribed to the transition of 4G5/2 → 6HJ (J = 5/2, 7/2, 11/2) respectively [28]. It

(3)

where Icry is the crystallinity index, Dp is the particle size (obtained from TEM), Dcry is the particle size from Scherrer's method. Icry is found to be ~4.0 which represents the polycrystalline nature of the obtained 3

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

K. Dhanalakshmi et al.

Fig. 3. (a, b) SEM micrographs, (c) TEM and (d) HRTEM of Y2SiO5:Smx3+ nanophosphor.

out to the data of PL intensity with doping concentration and slope was found to be 0.79 which shows energy transfer between the dopant and host resulting in the quenching. In the application of phosphor, CIE co-ordinates from the chromaticity diagram of the Commission International de Eclariage (CIE) are highly useful in determining the color purity of the sample. Thus the CIE chromaticity coordinates of Sm3+ doped Y2SiO5 samples were calculated from the spectra under 404 nm excitation wavelength. In Fig. 8, the CIE co-ordinates of the optimum concentration of Sm3+ doped Y2SiO5 is shown in CIE 1931 chromaticity diagram. The correlated color temperature (CCT) is a specification of the color appearance of the light emitted by a lamp, relating its color to the color of light from a reference source when heated to a particular temperature, measured in degrees Kelvin (K). Therefore, the quality of light emitted is represented by the color correlated temperature (CCT), which is calculated by using Mc. Camy empirical formula and is given by [32].

is also worth mentioning that among the observed transitions one at 600 nm is found to be highest in intensity compared to other peaks. It is known that the magnetic dipole (MD) transitions obey the selection rule ΔJ = 0 and ± 1 (J is the angular momentum) and electric dipole (ED) transitions obey the selection rule ΔJ ≤ 6 unless J or J1 = 0 when ΔJ = 2, 4, 6 [29]. In the case of Sm3+ ions, the 4G5/2 → 6H5/2 (ΔJ = 0) at 561 nm and 4G5/2 → 6H7/2 (ΔJ = 1) at 600 nm belong to MD transitions, while the 4G5/2 → 6H9/2 (ΔJ = 2) at 646 nm is related to an ED transition which was sensitive to the crystal field [29,30]. When Sm3+ ions occupy lattice sites with inversion centers, the 4G5/2 → 6H5/ 2(magnetic dipole) emission transition (around 590–600 nm) usually dominates; when the Sm3+ ions are located in the sites without inversion symmetry, the 4G5/2 → 6H9/2 (electric dipole) emission transition (around 610–630 nm) plays a crucial role, although other emission lines are also present. In order to study this effect on symmetry, the intensity ratio of ED to MD i.e. I(4G5/2 → 4H9/2)/I(4G5/2 → 4H5/2) taken and shown in Fig. 6. This intensity ratio parameter is often used as a sensitive parameter to understand the variation in the local symmetry around Sm3+ in the lattice [30]. In the present work, the 4G5/2 → 6H9/2 transition of Sm3+ is less intense than 4G5/2 → 6H5/2 transition, indicating that Sm3+ occupies the site with inversion symmetry in Y2SiO5 host. Furthermore, PL intensity increases with increasing the dopant concentration up to 5 mol% of Sm3+ and then decreases. Therefore, optimum concentration of Sm3+ in Y2SiO5 host was found to be 5 mol% (see Fig. 7). The concentration quenching pathways of Sm3+ in Y2SiO5 phosphor with various concentrations were calculated. The possible mechanism processes are mainly electric multipole interaction which was clearly described by the Van Uitert's equation [31].

1 x = θ X ⎡1 + β(x ) 3 ⎤ ⎣ ⎦

CCT = −437n3 + 3601n2 − 6861n + 5514.31

(6)

where, n = (x − xe) / (y − ye) and the chromaticity epicenter is at xe = 0.5952 and ye = 0.4034. The calculated CIE co-ordinates and CCT value of the all dopant concentration is represented in Table 1. 4. Thermoluminescence (TL) studies Effect of different concentrations of Sm3+ from 1 to 7 mol% on TL response of Y2SiO5:Sm3+ nanophosphor was studied (Fig. 9). Therefore, the TL glow curve with the variable concentrations of Sm3+ (1–7 mol %) were recorded for constant gamma irradiation and at constant heating rate of 3 °C s− 1. It was noticed that the integrated area of the curve for gamma dose increases with increasing Sm3+ concentrations up to 5 mol%. Further the glow peak structure remains same for all the concentrations of Sm3+ except shift in peak position; however the TL intensity varies with Sm3+ concentrations. The peak shift to higher

(5)

By using Van Uitert's relationship, a non-linear fitting was carried 4

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

K. Dhanalakshmi et al.

2.04 2.02

Ir

2.00 1.98 1.96 1.94 1.92 0.02

0.04

0.06

0.08

3+

Sm Conc. Fig. 6. Variation of the relative intensities (IR) with Sm3+ concentrations.

604 nm 565 nm

6000

PL Intensity (a.u)

5000 4000 3000 2000 1000

1 Fig. 4. (a) UV–visible spectra and (b) band gap of Y2SiO5:Smx3+.

6000

4 6 G5/2 H7/2

Intensity (a.u)

4000 4 6 G5/2 H5/2

4 6 G5/2 H9/2

0 575

600

625

650

5

6

7

8

9

TL intensity is due to the concentration quenching which destroys of trap levels [33]. To examine the material for its application in gamma ray dosimetry, the phosphor was exposed to a range of gamma dose from 300 Gy to 600 Gy at heating rate 3 °C s− 1. The recorded glow curves are presented in Fig. 10. The glow curve has two peaks namely low temperature peak at 245 °C and high temperature peak at 435 °C. TL response of the glow peak increased with increase in gamma dose. By the knowledge of literature the increase in the TL intensity with dose is because of the filling of more and more traps responsible for the TL peak. On heating, the trapped charge carriers were released and further recombined with their counter parts at the recombination centers resulted in the increase in TL Intensity [34]. The high temperature peak increases then decreases with increase in dose and finally vanish. This irregularity in the variation of TL peaks may be explained by Track Interaction model [35,36]. In general, trapping center or luminescence center TCs/LCs density generated during irradiation is proportional to the dose. As per TIM, the density of TCs/LCs produced by the gamma irradiation is proportional to the cross section of the track and the length of the track produced by the ion irradiation inside the matrix. The initial increase in TL intensity with dose can be explained by the recombination at low dose of various trapping/luminescent centers (TCs/LCs) that occurred completely within the tracks. The fast saturation of the 435 °C might be due to the formation of additional trapping

2000

550

4

Fig. 7. Variation of emission intensity on Sm3+ concentrations in Y2SiO5:Smx3+.

1 mol% 3 mol% 5 mol% 7 mol% 9 mol%

1000

3

3+ Sm (Conc.)

λexc= 408 nm

5000

3000

2

675

700

Wavelength (nm) Fig. 5. Photoluminescence emission spectra of Y2SiO5:Smx3+ nanophosphor excited at 408 nm.

temperature side with increase in Sm3+ concentration may be due to the creation of deeper trap levels. Deep traps created with increase in Sm3+ concentration requires more energy to get de-trap and demands higher temperature. The intensity of TL glow curve increases with increase in the dopant (Sm3+) concentration up to 5 mol% and then decreases with further increase in Sm3+ concentration. The decrease in 5

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

O

o

245 C

-1

HT: 3 Cs

16000 12000 8000 4000

O

435 C

Do

se

(G y)

0 600 500 400 300

TL Intensity (a.u.)

K. Dhanalakshmi et al.

100 150 200 250 300 350 400 450

Temperature (oC) Fig. 10. Effect of γ-dose on TL glow curves of Y2SiO5:Smx3+ nanophosphor at a heating rate of 3 °C s− 1.

corresponds to each peak is one of the important aspect of the TL study for any material as values for these parameters reveal information about the defect model with which they are associated. Therefore, in order to analyze the TL glow curves of the materials or to extract data from a TL glow curve, Chen's peak shape method [38] is used for the approximation of kinetic parameters by deconvolution of the dose response of the each sample as shown in Fig. 11.

Fig. 8. Color coordinates of Y2SiO5:Smx3+ (Sm3+ = 5 mol%) excited at 408 nm in CIE 1931 chromaticity diagram. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Table 1 Estimated CIE co-ordinates and CCT values for Y2SiO5:Smx3+ nano phosphor. 3+

conc. Sm (mol %)

2

kT m ⎞ Eα = cα ⎛ − bα (2kTm) ⎝ α ⎠ ⎜

CIE co-ordinates

1 3 5 7 9

CCT (K)

X

Y

0.552 0.545 0.554 0.546 0.549

0.445 0.450 0.445 0.450 0.450

⎟

(7)

where α = τ, δ and ω with τ = Tm − T1, δ = T2 − Tm and ω = T2 − T1

Cτ = 1.51 + 3.0(μ g − 0.42), 1998 2046 1976 2086 2041

bτ = 1.58 + 4.2(μ g − 0.42)

Cδ = 0.976 + 7.3(μ g − 0.42),

bδ = 0

Cω = 2.52 + 10.2(μ g − 0.42),

bω = 1

The form factor (symmetry factor; μg) is given by

16000

a. undoped b. 1 mol% c. 3 mol% d. 5 mol% e. 7 mol% f. 9 mol%

d

2450C

T2 − Tm T2 − T1

c

where Δ =

8000

(8)

βE −E ⎫ [1 + (b − 1)Δm] = s exp ⎧ 2 ⎨ kTm 2 ⎭ ⎩ kTm ⎬ 2kT ; E

Δm =

2kTm E

(9)

and β is the linear heating rate and k is

10000

b

experimental peak Deconvoluted peaks Fitted cure

Dose= 500 Gy a

4000

8000

TL Intenstiy (a.u)

TL Intensity (a.u)

12000

μg =

e

0 100

f

150

200

250 o Temperature ( C)

300

350

Fig. 9. TL glow curves of Y2SiO5:Smx3+ irradiated with 300 Gy γ-dose.

centers or that the increase in dose increased the trap levels resulting in the complex/clustered defects which lead to the decrease in the TL signal [37]. The characteristic of the TL glow curve is associated with kinetic parameters such as activation Energy (E): frequency factor (s) and the order of the kinetics (b). The determination of these parameters

6000

4000

2000

0 100

200

300

400

500

o Temperature ( C) Fig. 11. Glow curve deconvolution of 500 Gy γ-irradiated Y2SiO5:Smx3+ nanophosphor.

6

Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx

K. Dhanalakshmi et al.

RHK is grateful to Dr. B.M. Nagabhushana, HOD, Chemistry, M.S. Ramaiah Institute of Technology, Bangalore, for his constant support and encouragement.

Table 2 Estimated kinetic parameters of Y2SiO5:Smx3+ nanophosphor for different γ-doses. Dose (Gy)

300

400

500

600

Peak

1 2 3 1 2 3 1 2 3 1 2 3

Tm

174 226 417 175 227 431 165 237 430 189 237 388

b (μg)

2 2 2 2 2 2 2 2 2 2 2 2

(0.49) (0.53) (0.49) (0.50) (0.49) (0.49) (0.49) (0.51) (0.53) (0.53) (0.49) (0.48)

Activation energy (eV) Eτ

Eδ

Eω

Eave

Frequency factor S (s− 1)

0.728 1.465 1.919 0.827 1.262 1.343 1.091 0.802 1.566 1.096 0.964 0.625

0.784 1.408 1.924 0.869 1.28 1.409 1.109 0.857 1.559 1.073 1.022 0.75

0.759 1.441 1.933 0.852 1.278 1.383 1.106 0.833 1.568 1.088 0.997 0.684

0.757 1.438 1.926 0.849 1.273 1.378 1.102 0.83 1.564 1.086 0.994 0.686

4.0E + 09 6.3E + 15 1.5E + 15 4.7E + 10 1.1E + 14 6.4E + 10 8.8E + 13 1.6E + 09 1.6E + 12 1.1E + 13 8.0E + 10 7.6E + 12

References [1] Lili Han, Chao Guo, Zhipeng Ci, Chengwei Wang, Yuhua Wang, Yan Huang, Chem. Eng. J. 312 (15) (2017) 204–219. [2] M. Saif, N. Alsayed, A. Mbarek, M. El-Kemary, M.S.A. Abdel-Mottaleb, J. Mol. Struct. 1125 (5) (2016) 763–771. [3] Guiqiang Chen, Fengli Wang, Jie Yu, Haisheng Zhang, Xiao Zhang, J. Mol. Struct. 1128 (15) (2017) 1–4. [4] JiangKun Cao, FangFang Hu, LiPing Chen, Hai Guo, Changkui Duan, Min Yin, J. Alloys Compd. 693 (5) (2017) 326–331. [5] L. Shirmane, C. Feldmann, V. Pankratov, Phys. B Condens. Matter 504 (1) (2017) 80–85. [6] J. Marcazzó, M. Prokić, M. Santiago, P. Molina, E. Caselli, Nucl. Instrum. Methods Phys. Res., Sect. B 267 (19, 1) (2009) 3347–3350. [7] D.W. Cooke, B.L. Bennett, R.E. Muenchausen, K.J. McClellan, J.M. Roper, M.T. Whittaker, J. Appl. Phys. 86 (1999) 5308. [8] Yu. Zorenko, V. Gorbenko, T. Zorenko, T. Voznyak, A. Voloshynovskii, V. Vistovskiy, K. Paprocki, L. Mosińska, P. Bilski, A. Twardak, A. Fedorov, M. Nikl, J.A. Mares, J. Lumin. 179 (2016) 445–450. [9] Yu. Zorenko, V. Gorbenko, T. Zorenko, P. Malinowski, V. Jary, R. Kucerkova, A. Beitlerova, J.A. Mares, M. Nikl, A. Fedorov, J. Lumin. 154 (2014) 525–530. [10] Qingshan Lu, Jiangong Li, Opt. Mater. 33 (3) (2011) 381–384. [11] Murat Erdem, Olgun Erguzel, Mete K. Ekmekci, Humeyra Orucu, Hatun Cinkaya, Seval Genc, Ayhan Mergen, Gonul Eryurek, Baldassare Di Bartolo, Ceram. Int. 41 (10 Part A) (2015) 12805–12810. [12] Jianbei Qiu, Qing Jiao, Dacheng Zhou, Zhengwen Yang, J. Rare Earths 34 (4) (2016) 341–367. [13] J. Zmojda, M. Kochanowicz, P. Miluski, M. Leśniak, M. Sitarz, W. Pisarski, J. Pisarska, D. Dorosz, J. Mol. Struct. 1126 (15) (2016) 207–212. [14] D.L. Monika, H. Nagabhushana, S.C. Sharma, B.M. Nagabhushana, R. Hari Krishna, Chem. Eng. J. 253 (2014) 155–164. [15] P. Haritha, C.S. Dwaraka Viswanath, K. Linganna, P. Babu, C.K. Jayasankar, V. Lavín, V. Venkatramu, J. Lumin. 179 (2016) 533–538. [16] Xinyang Zhang, Yuxue Liu, Meng Zhang, Jian Yang, Hancheng Zhu, Duanting Yan, Chunguang Liu, Changshan Xu, Mater. Res. Bull. 86 (2017) 51–56. [17] Pengfei Feng, Jiachi Zhang, Qingsong Qin, Rui Hu, Yuhua Wang, Mater. Res. Bull. 50 (2014) 365–368. [18] K.C. Patil (Ed.), Chemistry of Nanocrystalline Oxide Materials, 2008. [19] Yixiu Luo, Jiemin Wang, Jingyang Wang, Junning Li, Zijun Hu, J. Am. Ceram. Soc. 97 (3) (2014) 945–951. [20] B.D. Cullity, Elements of X-ray Diffraction, Addison-Wesley, 1956. [21] P. Klug, L.E. Alexander, X-ray Diffraction Procedure, Wiley, New York, 1954. [22] G. Ramakrishna, H. Nagabhushana, S.C. Prashantha, S.C. Sharma, B.M. Nagabhushana, Spectrochim. Acta B Mol. Biomol. Spectrosc. 136 (5) (2015) 356–365. [23] X.M. Han, J. Lin, J. Fu, R.B. Xing, M. Yu, Y.H. Zhou, M.L. Pang, Solid State Sci. 6 (4) (2004) 349–355. [24] M.N. Rifaya, T. Theivasanthi, M. Alagar, Nanosci. Nanotechnol. 2 (5) (2012) 134–138. [25] J. Tauc, F. Abeles (Ed.), Optical Properties of Solids, North Holland Publishers, Amsterdam, 1970. [26] Alex Dolgonos, Thomas O. Mason, Kenneth R. Poeppelmeier, J. Solid State Chem. 240 (2016) 43–48. [27] R. Hari Krishna, B.M. Nagabhushan, H. Nagabhushana, R.P.S. Chakradhar, R. Sivaramakrishna, C. Shivakumara, Tiju Thomas, J. Alloys Compd. 585 (2014) 129–137. [28] R. Hari Krishna, B.M. Nagabhushana, Baburao N. Sherikar, N. Suriya Murthy, C. Shivakumara, Tiju Thomas, Chem. Eng. J. 267 (2015) 317–323. [29] G. Seeta Rama Raju, Jae Su, Spectrochim. Acta B Mol. Biomol. Spectrosc. 124 (2014) 383–388. [30] T. Suhasini, J. Suresh Kumar, T. Sasikala, K. Jang, H.S. Lee, M. Jayasimhadri, J.H. Jeong, S.S. Yi, L. Rama Moorthy, Opt. Mater. 31 (2009) 1167–1172. [31] Z. Wang, P. Li, Z. Yang, Q. Guo, J. Lumin. 132 (2012) 1944–1948. [32] C.S. McCamy, Color. Res. Appl. 17 (1992) 142. [33] Numan Salah, Radiat. Phys. Chem. 80 (1) (2011) 1–10. [34] S.P. Lochab, D. Kanjilal, N. Salah, S.S. Habib, J. Lochab, R. Ranjan, V.E. Aleynikov, A.A. Rupasov, A. Pandey, J. Appl. Phys. 104 (2008) 033520–033523. [35] Y.S. Horowitz, M. Rosenkrantz, S. Mahajana, D. Yosian, J. Phys. D. Appl. Phys. 29 (1996) 205–217. [36] R. Hari Krishna, B.M. Nagabhushana, H. Nagabhushana, N. Suriya Murthy, S.C. Sharma, C. Shivakumara, R.P.S. Chakradhar, J. Phys. Chem. C 117 (4) (2013) 1915–1924. [37] M.V. Ramana Reddy, C.H. Gopal Reddy, K. Narasimha Reddy, Bull. Mater. Sci. 30 (1) (2007) 1–3. [38] R. Chen, S.W.S. Mckeever, Dermatol. Sin. (1997).

Boltzmann constant (8.6 × 10− 5 eV K− 1), (s) = frequency factor and (b) = order of the kinetics. Activation energy is the energy required to eject the trapped charge carriers from the trapping center/defect center to the conduction band. The activation energy lies in between 0.68 and 1.48 eV. Nature of the kinetics obeyed by the glow peak can be estimated by form/shape factor in turn order of kinetics. The value of shape factor lies in between 0.48 and 0.51 which is near to 0.52 so the results confirms the presence of second order peak. Frequency factor (s) is one of the important TL parameter which gives statics about the possibility to eject charge carriers from their trap/defect center after exposed to radiation. The value of frequency factor is proportional to the ability of the material to keep the dose information inside it for a period of time. The estimated parameters are tabulated in Table 2 the frequency factor is in order of 1015 s− 1 and average energy range required to eject an electron from the trap center is 0.7 to 1.9 eV. 5. Conclusions Sm3+ doped Y2SiO5 (1 mol%–11 mol%) nanopowders were synthesized by a low-temperature solution combustion method using ODH fuel. Monoclinic structure of Y2SiO5 without secondary phase with crystallite size in the range of ~25–40 nm was confirmed from XRD results. The characterization of the samples confirmed that doping of Sm3+ substitute the yttrium with six co-ordination sites. SEM and TEM images reveal a highly porous and irregular structure, agglomerated nanoparticles with sizes in the range of ~40–50 nm consistent with XRD results. Photoluminescence (PL) under 408 nm excitation shows characteristic emission peaks at 561, 571, 600 and 646 nm which are ascribed to the transition of 4G5/2 → 6HJ (J = 5/2, 7/2, 11/2) respectively. The 4G5/2 → 6H9/2 transition of Sm3+ is more intense than 4G5/ 6 3+ occupies the site without 2 → H5/2 transition, indicating that Sm inversion symmetry in Y2SiO5 host. The Thermoluminescence (TL) glow curve has two peaks, low temperature peak at 245 °C and high temperature peak at 435 °C. The intensity of TL glow curve at 245 °C increases with increase in the dopant (Sm3+) concentration up to 5 mol% and then decreases with further increase in Sm3+ concentration. Chen's peak shape method analysis of the experimental TL glow curve confirms the presence of second order kinetics. Acknowledgments Authors, AJR and RHK are thankful to the Management and Principal of M.S. Ramaiah Institute of Technology, Bangalore, for the encouragement and facilities provided for carrying the research work.

7