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ARTICLE IN PRESSG ModelJLEO-55166; No. of Pages 5

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Contents lists available at ScienceDirect

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hotoluminescence and thermoluminescence behavior of Gd doped2O3 phosphor

ikas Dubeya,b,∗, Sadhana Agrawalb, Jagjeet Kaurc

Department of Physics, Bhilai Institute of Technology Raipur, New Raipur, Chhattisgarh, IndiaDepartment of Physics, National Institute of Technology, Raipur, Chhattisgarh, IndiaDepartment of Physics, Government V.Y.T.PG. Autonomous College, Durg, Chhattisgarh 91001, India

r t i c l e i n f o

rticle history:eceived 9 November 2013ccepted 8 June 2014vailable online xxx

eywords:hotoluminescencehermoluminescenceIE techniques

a b s t r a c t

The present paper reports the synthesis and characterization photoluminescence and thermolumi-nescence studies of Gd3+ doped Y2O3 phosphors. The effect of variable concentration of europium onphotoluminescence (PL) and thermoluminescence (TL) behavior are also studied. The samples were pre-pared by solid state synthesis technique which is suitable for large scale production of phosphors. Thestarting materials used for sample preparation are ZrO2 and Gd2O3 and CaF2 used as a flux. The preparedsample was characterized by X-ray diffraction technique (XRD). The surface morphology of preparedphosphor was determined by field emission gun scanning electron microscopy (FEGSEM) technique. Thediffraction pattern was measured by transmission electron microscopy (TEM) with selected area diffrac-tion pattern. All prepared phosphor with variable concentration of Gd3+ (0.2–2 mol%) was studied byphotoluminescence analysis it is found that the excitation spectra of prepared phosphor shows broadexcitation centered at 249 and 254 nm with few shoulder weak peaks at 275, 308 and 315 nm. The exci-

3+

tation spectra with variable concentration of Gd show strong peaks at 613 nm for 254 nm excitation.For 275 nm excitation strong peaks found at 468, 567, 578 and 608 nm. For recording TL glow curve everytime 2 mg phosphor was irradiated by UV 254 nm source and fixed the heating rate at 6.7 ◦C s−1. Sam-ple shows well resolved peak at 97 ◦C for 2 mol% of Gd3+. Trapping parameters are calculated for everyrecorded glow curve.

© 2014 Elsevier GmbH. All rights reserved.

. Introduction

Since a short-wavelength UV light of mercury vapour plasma isommonly used as an excitation source in most commercially avail-ble lamps, the optimization of luminescence quantum efficiency ofhosphors is required for the 254 nm excitation in the fluorescent

ight products [1]. Nevertheless, the disposing of the used vapourunk causes environmental contamination. Recent investigation oneep violet light-emitting devices and lasers quite possibly pro-ides an alternative excitation in the range of 340–400 nm [2–8].ttrium sesquioxide (Y2O3) ceramics have been intensively inves-igated for different technological purposes. For decades, yttrium

Please cite this article in press as: V. Dubey, et al., PhotoluminescenceOptik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijl

xide has been an important material in the ceramic industry, fromeing a constituent of ceramic super-conductors [9], to well-knownSZ ceramics [10]. Y2O3 is used in electronic applications as a part

∗ Corresponding author at: Department of Physics, Bhilai Institute of Technologyaipur, New Raipur, Chhattisgarh, India. Tel.: +91 09826937919.

E-mail address: jsvikasdubey@gmail.com (V. Dubey).

ttp://dx.doi.org/10.1016/j.ijleo.2014.06.175030-4026/© 2014 Elsevier GmbH. All rights reserved.

of metal–oxide–semiconductor hetero structures in Metal OxideSemiconductor (MOS) transistors [11]. It also plays an importantrole in the preparation of novel light-emitting materials [12,13].Host materials with a wide band gap are attractive for optical appli-cations in the visible and UV spectral ranges [14,15], because therare earths can emit within its optical window and do not suffer ofquenching effects inherent to semiconductor hosts [16,17].

The present paper reports the synthesis of Y2O3 phosphor withvariable concentration of gadolinium (0.2–2 mol%). All samples wasprepared by solid state reaction techniques and characterized byXRD, FEGSEM, TEM, PL and TL studies. The particle size of preparedphosphor was calculated by Scherer’s formula. The average particlesize of prepared phosphors found in the range 70–100 nm. All sam-ple shows cubic structure of Y2O3. There is no impurity phase founddue to the concentration of gadolinium. FEGSEM study shows thesurface morphology of prepared phosphor. The obtained sample

and thermoluminescence behavior of Gd doped Y2O3 phosphor,eo.2014.06.175

shows an intense blue, greenish and red-white emission (rangingfrom 400 to 650 nm), under a wide range of UV light excitation(220–400 nm). The PL spectra recorded for different concentrationof gadolinium. The PL emission intensity increases with increasing

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ble region and useful for potential candidate for LED (Light EmittingDiode) application (Ex.275) as well as for FL (Fluorescent Lamp) andCompact Fluorescent Lamp (CFL) (Ex.254 nm).

Fig. 1. Powder XRD pattern of Y2O3: Gd (0.5–1.5 mol%) doped phosphor.

he gadolinium concentration up to 1.5 mol% after that the intensityecreases due to concentration quenching occurs. The results indi-ate that Y2O3:Gd (1.5%) phosphors can be selected as a potentialandidate for LED application (Ex.275) as well as for Fluorescentamp phosphor as well as Compact fluorescent lamps (Ex.254).pectrophotometric determination was done for PL emission inommission Internationale de I’Eclairage (CIE) technique. The opti-ized sample was studied by TL glow curve with variable UV dose

t fixed concentration of Gd and fixed heating rate.

. Experimental

To prepare Y2O3 with gadolinium (0.2–2 mol%) consists of heat-ng stoichiometric amounts of reactant mixture is taken in aluminarucible and is fired in air at 1300 ◦C for 4 h in a muffle furnace. Everyeating is followed by intermediate grinding using agate mortarnd pestle. The Gd activated Y2O3phosphor was prepared via highemperature modified solid state diffusion. The starting materialsere as follows: Y2O3, Gd2O3 and CaF2 (as a flux) in molar ratioere used to prepare the phosphor [18,26].

The sample was characterized using photoluminescence (PL),hermoluminescence (TL), XRD, FEGSEM and HRTEM. The XRD

easurements were carried out using Bruker D8 Advance X-rayiffractometer. The X-rays were produced using a sealed tube andhe wavelength of X-ray was 0.154 nm (Cu K-alpha). The X-raysere detected using a fast counting detector based on Silicon

trip technology (Bruker LynxEye detector). Observation of parti-le morphology was investigated by FEGSEM (field emission guncanning electron microscope) (JEOL JSM-6360). The photolumi-escence (PL) emission and excitation spectra were recorded atoom temperature by use of a Shimadzu RF-5301 PC spectrofluo-ophotometer. The excitation source was a xenon lamp. Thermallytimulated luminescence glow curves were recorded at room tem-erature by using TLD reader I1009 supplied by Nucleonix Sys. Pvt.td., Hyderabad. The obtained phosphor under the TL examinations given UV radiation using 254 nm UV source [19–21,27–29].

. Results and discussion

The prepared phosphor materials were analyzed by PXRD toeveal phase compositions and the particle size (Fig. 1). The crystal-ite size was calculated from the PXRD pattern following the Schererquation D = 0.9�/ ̌ cos �. Here, D is the crystallite size for the (hkl)

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lane, � is the wavelength of the incident X-ray radiation [CuK˛0.154056 nm)], ̌ is the full width at half maximum (FWHM) inadians, and � is the diffraction angle for the (hkl) plane. From theXRD pattern, it was found that the prominent phase formed is

Fig. 2. FEGSEM image of Y2O3:Gd (1.5 mol%).

Y2O3, after the diffraction peaks as well indexed based on the ICDDNo. 89-5591. This reveals that the structure of Y2O3 is cubic [18,26].

3.1. FEGSEM and HRTEM

Field emission gun scanning electron microscopy and high res-olution transmission electron microscopy images are shown inFigs. 2 and 3. From the images that confirms the formation ofphosphor. The prepared sample shows a compact distribution overthe surface and good connectivity between grains. Similarly theHRTEM SAED (selected area electron diffraction) pattern image isthe diffraction pattern that is similar as XRD pattern. The particleshad a narrow size distribution, a rugby-like shape and a diameterof 70–100 nm. Some agglomerates formation occurs in the paperedsample.

4. Photoluminescence study

Fig. 4 shows the PL excitation spectra of prepared phosphor(Y2O3:Gd), excitation spectra recorded at 613 nm excitation. Peaksfound 249, 254, 275, 308 and 315 nm. The band near 254 nm isknown to be a charge transfer (CT) process that is related to theexcitation of an electron from the oxygen 2p state to a Gd3+ 4f state.

The emission spectrum of phosphors was recorded by exci-tations with, 254 and 275 nm. The emission peaks found at400–650 nm range (Figs. 5 and 6) more intense peaks at 468, 567,574, 608 and 618 nm. Its shows that the all emission belongs in visi-

and thermoluminescence behavior of Gd doped Y2O3 phosphor,eo.2014.06.175

Fig. 3. HRTEM image of Y2O3:Gd.

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4204003803603403203002802602402202000

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315 nm308nm

275 nm

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Fig. 4. PL Excitation spectra of Y2O3:Gd doped phosphor monitored with 613 nm.

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0.1mol% Gd

0.5mol% Gd613nm

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ig. 5. PL emission spectra of Y2O3:Gd (0.2–2 mol%) doped phosphor monitoredith 254 nm.

It is very interesting results found from PL emission spectra at54 nm excitation (Fig. 5). The effect of variable concentration ofadolinium on PL study shows linear response with doing concen-ration up to 1.5 mol% of Gd3+ after that concentration quenchingccurs and PL intensity decreases with increasing the dopant con-entration. So the optimized concentration is 1.5 mol% of Gd in Y2O3ost. A different observation in PL emission spectra was found for75 nm excitation (Fig. 6). All peaks found in visible region (468,67, 583, 608 and 618 nm) these all peaks indicate that the singleost with single dopant shows composed white light so it may beseful for white light emitting diode (WLED) application.

.1. Thermoluminescence study

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The glow curve is characteristic of the different trap levels thatie in the band gap of the material. A reliable dosimetric study of ahermoluminescent material should be based on a good knowledge

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Y2O3 (Gd 1%) Excitation at 275nm

468

ig. 6. PL emission spectra of Y2O3:Gd doped phosphor monitored with 275 nm.

Fig. 7. TL glow curve of Y2O3:Gd Phosphor with the variation of UV exposure time(5–20 min).

of its kinetic parameters that include trap depth (E), order of kinet-ics (b) and frequency factor (s). The study of relatively deep trappingdefect-states in various phosphors, as well as TL dating of solid statematerials, is closely related to the position of the trapping levelswithin the forbidden gap. Although there are various methods toobtain the number of glow peaks in the complex glow curves andtheir kinetic parameters that best describe the peaks [22].

To gain some idea of the characteristic glow curves of the syn-thesized Y2O3:Gd3+samples, the TL glow curves were obtained byheating samples from 50 up to 400 ◦C at a heating rate of 6.7 ◦C s−1.The glow curves of synthesized Y2O3:Gd (Fig. 7) with the variationof UV exposure time 5–20 min. Prominent peak found at 95 ◦C andsample shows the second order kinetics which is determined byshape factor. The values of kinetic parameters for Y2O3:Gd (1 mol%)is given in Table 1. The peak shape factor for the TL glow curve ofthe prepared phosphor was found to be ∼0.5 for maximum peaks.

For variable concentration of Gd3+ in Y2O3 host in thermolu-minescence glow curve shows very good interesting result. The TLintensity increase with increasing the concentration of Gd3+ up to1.5 mol% thereafter the intensity decreases due to concentrationquenching occurs. Here the optimized TL is Y2O3:Gd3+(1.5 mol%)which is suitable for dosimetric application on TL.

4.2. Determination of kinetic parameters

The TL glow curve is related to the trap levels lying at differentdepths in the band gap between the conduction and the valencebands of a solid. These trap levels are characterized by differenttrapping parameters such as trap depth, order of kinetics, and fre-quency factor [25,30–34]. The loss of dosimetry information stored

and thermoluminescence behavior of Gd doped Y2O3 phosphor,eo.2014.06.175

in the materials after irradiation is strongly dependent on the posi-tion of trapping levels within the forbidden gap which is known astrap depth or activation energy (E). The mechanism of recombina-tion of detrapped charge carriers with their counter parts is known

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Table 1shape factor (�), activation energy (E) and frequency factor (s) of UV irradiated Y2O3:Gd (1 mol%).

UV min T1 Tm T2 � ı ω � = ı/ω Activation energy (E) eV Frequency factor (s) s−1

5 min 70 97 134 27 37 64 0.57 0.67 2 × 1010

10 min 70 95 128 25 33 58 0.56 0.71 1 × 1011

15 min 70 95 130 25 35 60 0.58 0.71 1 × 1011

20 min 76 101 131 25 30 55 0.54 0.73 1 × 1011

Fm

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E

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ig. 8. Representative diagram of different parameters used in the glow-curve shapeethod [24].

s the order of kinetics (b). The frequency factor (s) represents theroduct of the number of times an electron hits the wall and theall reflection coefficient, treating the trap as a potential well. Thus,

iable dosimetry study of thermoluminescent material is based onts trapping parameters.

Here each of the glow curves analyzed based on glow curvehape method [23] (Fig. 7). The order of kinetic of glow curves wasalculated by measuring symmetry (geometrical) factor �g ∼ 0.5Fig. 8). The values of �, ı and ω are calculated, where ‘�’ is the low-emperature half width of the glow curve i.e. � = Tm − T1, ‘ı’ is theigh-temperature half width of the glow curve i.e. ı = T2 − Tm and

ω’ is the full width of the glow peak at its half height i.e. ω = T2 − T1.rom the value of geometrical factor it is clear that the glow peaksbey the general order kinetics. The trap depth also known as thectivation energy of the luminescence centers is calculated usinghen’s equation [23]

˛ = C˛

(kBT2

m

˛

)− b˛(2Tm) (1)

here kB is Boltzmann constant. Tm is peak temperature. The con-tant C˛ and b˛ were also calculated by the Chen’s equation. Theean activation energy was found to be ∼0.67 and ∼0.73 eV for 95

nd 101 ◦C and value of frequency factor lies in between 2 × 1010

nd 1 × 1011 s−1.The CIE coordinates were calculated by Spectrophotometric

ethod using the spectral energy distribution of the Y2O3:Gd sam-le (Fig. 9). The color co-ordinates for the Gd doped sample are

= 0.42 and y = 0.32 (these coordinates are very near to the whiteight emission). Hence this phosphor having excellent color ten-bility from white light emission.

. Conclusion

Y2O3:Gd doped phosphor synthesized by modified solid stateeaction method. XRD pattern confirms that synthesized sam-le shows cubic structure. The crystallites size was found to be0–100 nm range. XRD studies confirm the phosphors are in singlehase and nano crystallites. FEGSEM images show the formation of

Please cite this article in press as: V. Dubey, et al., PhotoluminescenceOptik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijl

hosphors. The PL emission was observed in the range 400–650 nmor the Y2O3 phosphor doped with Gd. Excitation spectrum foundt 254 and 275 nm. Sharp peaks found around 468, 569, 574, 608nd 618 nm with high intensity. The present phosphor can act as

[

[

Fig. 9. CIE coordinates depicted on 1931 chart of Gd (1 mol%) doped Y2O3 phosphor.

single host for white light emission in display devices. The CIE 1931chromaticity coordinates much closer to the equal-energy white-light. Thermoluminescence glow curve shows linear response withdose which indicate that the prepared sample may be useful for TLdosimetry application. Also the trapping parameters are calculatedfor variable UV dose for single glow peak. All samples show the sec-ond order of kinetics. For the variable concentration Gd in TL studyshows linear response and the concentration quenching occurs for2 mol% of Gd3+. So the optimized TL is Y2O3:Gd3+(1.5 mol%) whichis suitable for dosimetric application on TL.

References

[1] Y. Sato, N. Takahashi, S. Sato, Full-color fluorescent display devices using a near-UV light-emitting diode, Jpn. J. Appl. Phys. 35 (Pt 2) (1996) 838.

[2] N. Ohashi, N. Ebisawa, T. Sekiguchi, I. Sakaguchi, Y. Wada, T. Takenaka, H.Haneda, Yellowish-white luminescence in codoped zinc oxide, Appl. Phys. Lett.86 (091) (2005) 902.

[3] X.Q. Piao, T. Horikawa, H. Hanzawa, K. Machida, Characterization and lumi-nescence properties of Sr2Si5N8:Eu2+ phosphor white light emitting-diodeillumination, Appl. Phys. Lett. 88 (161) (2006) 908.

[4] J.K. Park, C.H. Kim, S.H. Park, H.D. Park, S.Y. Choi, Application of strontiumsilicate yellow phosphor for white light-emitting diodes, Appl. Phys. Lett. 84(2004) 1647.

[5] R.J. Xie, N. Hirosaki, M. Mitomo, K. Takahashi, K. Sakuma, Highly efficient white-light-emitting diodes fabricated with short-wavelength, Appl. Phys. Lett. 88(101) (2006) 104.

[6] R. Xie, N. Hirosaki, K. Sakuma, Y. Yamamoto, M. Mitomo, Eu2+doped Ca-�-SiAlON: a yellow phosphor for white light-emitting diodes, Appl. Phys. Lett.84 (2004) 5404.

[7] N. Sagawa, T. Uchino, Visible luminescence from octadecylsilane monolayers onsilica surfaces: time-resolved photoluminescence characterization, Appl. Phys.Lett. 87 (251) (2005) 923.

[8] B. Liu, C. Shi, Z. Qi, Potential white-light long-lasting phosphor: Dy3+ dopedaluminate, Appl. Phys. Lett. 86 (191) (2005) 111.

[9] P. Regnier, M. Sapin, C. Thomas de Montpreville, On the substitution of Y2O3

with ZrO2 in the synthesis of YBa2Cu3O7, Supercond. Sci. Technol. 2 (1989) 173.10] M. Boaro, J.M. Vohs, R.J. Gorte, Synthesis of highly porous yttria-stabilized zir-

conia by tape-casting methods, J. Am. Ceram. Soc. 86 (2003) 395.11] J.J. Chambers, G.N. Pearson, Physical and electrical characterization of ultrathin

yttrium silicate insulators on silicon, J. Appl. Phys. 90 (2001) 918.

and thermoluminescence behavior of Gd doped Y2O3 phosphor,eo.2014.06.175

12] F. Vetrone, J.-C. Boyer, J.A. Capobianco, A. Speghini, M. Bettinelli, Concentrationdependent near infrared-to-visible upconversion in nanocrystalline and bulkY2O3:Er3+, Chem. Mater. 15 (2003) 2737.

13] A. Konrad, U. Herr, R. Tidecks, F. Kummer, K. Samwer, Luminescence of bulkand nanocrystalline cubic yttria, J. Appl. Phys. 90 (2001) 3516.

ING ModelI

ptik xx

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

ARTICLEJLEO-55166; No. of Pages 5

V. Dubey et al. / O

14] A. Patra, C.S. Friend, R. Kapoor, P.N. Prasad, Upconversion in Er3+: ZrO2

nanocrystals, J. Phys. Chem. B 106 (2002) 1909–1912.15] P. Salas, C. Angeles-Chavez, J.A. Montoya, E.D.L. Rosa, L.A. Diaz-Torres, H.

Desirenab, A. Martínez, M.A. Romero-Romo, J. Morales, Synthesis, characteriza-tion and luminescence properties of ZrO2:Yb3+–Er3+ nanophosphor, Opt. Mater.27 (7) (2005) 1295–1300.

16] F. Vetrone, J.C. Boyer, J.A. Capobianco, A. Speghini, M. Bettinelli, Effect of Yb3+

Co-doping on the upconversion emission in nanocrystalline Y2O3:Er3+, J. Phys.Chem. B 107 (5) (2003) 1107–1112.

17] D. Matsuura, Red, green and blue up-conversion luminescence of trivalent rarenanocrystals, Appl. Phys. Lett. 81 (2002) 4526–4528.

18] V. Dubey, J. Kaur, S. Agrawal, Synthesis and characterization of Eu3+-doped Y2O3 phosphor, Res. Chem. Intermed. (2013), http://dx.doi.org/10.1007/s11164-013-1201-5.

19] V. Dubey, J. Kaur, S. Agrawal, N.S. Suryanarayana, K.V.R. Murthy, Synthesis andcharacterization of Eu3+ doped SrY2O4 phosphor, Optik 124 (2013) 5585–5587.

20] V. Dubey, N.S. Suryanarayana, J. Kaur, Kinetics of TL glow peak of limestonefrom patharia of CG basin (India), J. Miner. Mater. Charact. Eng. 9 (12) (2010)1101–1111.

21] V. Dubey, J. Kaur, N.S. Suryanarayana, K.V.R. Murthy, Thermoluminescenceand chemical characterization of natural calcite collected from Kodwa mines,Res. Chem. Intermed. (2012), http://dx.doi.org/10.1007/s11164-012-0872-7.

22] S.W.S. McKeever, Thermoluminescence of Solids, Cambridge University Press,USA, 1985.

Please cite this article in press as: V. Dubey, et al., PhotoluminescenceOptik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijl

23] R. Chen, Y. Krish, Analysis of Thermally Stimulated Process, Pergamon Press,Oxford, 1981, pp. 159.

24] B.N. Lakshminarasappa, J.R. Jayaramaiah, B.M. Nagabhushana, Thermolumines-cence of combustion synthesized yttrium oxide, Powder Technol. 217 (2012)7–10.

[

PRESSx (2014) xxx–xxx 5

25] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer, Berlin, Germany,1994.

26] V. Dubey, J. Kaur, S. Agrawal, Effect of europium concentration on photolu-minescence and thermoluminescence behavior of Y2O3:Eu3+ phosphor, Res.Chem. Intermed. (2014), http://dx.doi.org/10.1007/s11164-014-1563-3.

27] V. Dubey, J. Kaur, S. Agrawal, N.S. Suryanarayana, K.V.R. Murthy, Effect of Eu3+

concentration on photoluminescence and thermoluminescence behavior ofYBO3:Eu3+ phosphor, Superlattices Microstruct. 67 (2014) 156–171.

28] J. Kaur, Y. Parganiha, V. Dubey, D. Singh, D. Chandrakar, Synthesis, characteriza-tion and luminescence behavior of ZrO2:Eu3+, Dy3+with variable concentrationof Eu and Dy doped phosphor, Superlattices Microstruct. 73 (2014) 38–53.

29] V. Dubey, J. Kaur, N.S. Suryanarayana, K.V.R. Murthy, Thermoluminescencestudy, including the effect of heating rate, and chemical characterization ofAmarnath stone collected from Amarnath Holy Cave, Res. Chem. Intermed.(2014), http://dx.doi.org/10.1007/s11164-012-0980-4.

30] R.K. Tamrakar, D.P. Bisen, I.P. Sahu, N. Brahme, UV and gamma ray inducedthermoluminescence properties of cubic Gd2O3:Er3+ phosphor, J. Radiat. Res.Appl. Sci. (2014), http://dx.doi.org/10.1016/j.jrras.2014.07.003.

31] R.K. Tamrakar, UV-irradiated thermoluminescence studies of bulk CdS withtrap parameter, Res. Chem. Intermed. (2013), http://dx.doi.org/10.1007/s11164-013-41166.

32] R.K. Tamrakar, D.P. Bisen, Optical and kinetic studies of CdS:Cu nanoparticles,Res. Chem. Intermed. 39 (2013) 3043–3048.

33] R.K. Tamrakar, D.P. Bisen, C.S. Robinson, I.P. Sahu, N. Brahme, Ytterbium dopedgadolinium oxide (Gd2O3:Yb3+) phosphor: topology, morphology, and lumi-

and thermoluminescence behavior of Gd doped Y2O3 phosphor,eo.2014.06.175

nescence behaviour in Hindawi publishing corporation, Indian J. Mater. Sci.2014 (2014), Article ID 396147.

34] R.K. Tamrakar, D.P. Bisen, K. Upadhyay, N. Bramhe, Effect of fuel on struc-tural and optical characterization of Gd2O3:Er3+ phosphor, J. Lumin. Appl. 1(1) (2014) 23–29.