Journal of Luminescence 143 (2013) 337–342

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Journal of Luminescence

0022-23http://d

n CorrE-m

journal homepage: www.elsevier.com/locate/jlumin

Photoluminescence and thermoluminescence properties of Dy3+/Eu2+

activated Na21Mg(SO4)10Cl3 phosphors

Bhushan P. Kore a, N.S. Dhoble b, K. Park c, S.J. Dhoble a,n

a Department of Physics, RTM Nagpur University, Nagpur 440033, Indiab Department of Chemistry, Sevadal Mahila Mahavidyalaya, Nagpur 440009, Indiac Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul 143-747, Korea

a r t i c l e i n f o

Article history:Received 16 December 2012Received in revised form20 April 2013Accepted 26 April 2013Available online 17 May 2013

Keywords:PhosphorsThermoluminescence (TL)Photoluminescence (PL)DeconvolutionNa21Mg(SO4)10Cl3

13/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.jlumin.2013.04.053

esponding author.ail address: sjdhoble@rediffmail.com (S.J. Dho

a b s t r a c t

In the present work luminescence properties of rare earth (RE) doped Na21Mg(SO4)10Cl3 were studied.Modified solid state method was employed to synthesize the phosphors. The influence of RE (RE¼Dy andEu) doping on the luminescence properties of as prepared phosphor were investigated in detail. PLemission spectra of the Na21Mg(SO4)10Cl3:Dy phosphor exhibits the characteristic emission of Dy. Thecharacteristic Dy3+ emission in the form of peaks around 482 and 576 nm corresponding to transitions4F9/2-6H15/2 and 4F9/2-6H13/2 was seen when excited by excitation wavelength 351 nm. However,interesting thermoluminescence results are observed in case of Dy as well as Eu doped Na21Mg(SO4)10Cl3.The TL glow curves for Na21Mg(SO4)10Cl3:Dy exhibit broad peak composed of three overlapping peaks,these peaks were deconvoluted using deconvolution program. The peaks at different temperaturesindicate that different sets of traps are being activated within the particular temperature range each withits own value of activation energy (E) and frequency factor (s). The peaks observed were due to formationof trap levels by γ-rays irradiation and subsequently activation of traps on thermal stimulation. Thetrapping parameters for both the samples were calculated using Chen's peak shape method and reportedin this paper.

& 2013 Elsevier B.V. All rights reserved.

1. Introduction

Thermoluminescence (TL) is a very important technique due to itsapplications in various fields such as radiation therapy, dosimetry,geology, space research and other research related areas [1–4]. Studieson radiation induced defects in insulating and semiconducting mate-rials have been interesting over the last few decades [5]. Severalmaterials such as LiF:Ti, Mg and α-Al2O3:C, CaSO4:Dy due to theirexcellent thermoluminescent properties such as high TL efficiency,dose response, thermal stability, high sensitivity and reproducibility,are now commonly used as thermoluminescent dosimeters (TLD) in agreat diversity fields of applications. The main applications of thesematerials are in radiation dosimetry, for personnel and environmentalmonitoring [6,7]. Many sensitive synthetic materials are developed forfulfilling the above mentioned properties [8,9]. Different preparativemethods [10,11] and thermoluminescent properties of several materi-als have been studied so far [12] and it is found that mixed alkali/alkaline sulfate constitute a class of thermoluminescence phosphorswith good performances, especially when doped with appropriateactivators [13]. Sulfate based TL materials are synthesized and studiedbecause of their well desired characteristics like a high temperature

ll rights reserved.

ble).

glow peak, linear response with ionizing radiation exposure, negligiblefading and an easy methods of preparation [14]. There are severalthermoluminescent materials such as CaSO4:Eu, Ag, K2Ca2(SO4)3:Eu,KMgSO4Cl doped with Dy, Ce andMn etc. of which almost all has beenstudied for improvement in the thermoluminescence characteristicsand the trapping parameters [15–17]. The study of the luminescence asa function of the temperature, the so called glow curve, is used todetermine the trapping parameters and its integral is proportional tothe radiation dose absorbed by the irradiated sample. The position,shape and intensities of the glow peaks are related to the properties oftraps responsible for the TL. The shape and position of the resultant TLglow curves can be analyzed to extract information about the variousparameters of the trapping process such as activation energy which isthe thermal energy required to liberate the trapped electrons andholes, frequency factor, trap depth, trapping and retrapping rates etc. Apopular method of analyzing a TL glow curve in order to ascertain thekinetic parameters E, s, and b is by considering the shape orgeometrical properties of the peak. TL glow peaks corresponding tosecond-order kinetics are characterized by an almost symmetricalshape, whereas first-order peaks are asymmetrical. Grossweinerwas the first to use the shape of the glow peak to calculate the trapdepth E [18].

In this paper, the kinetic parameters of Rare Earth (RE)-dopedNa21Mg(SO4)10Cl3 phosphor, synthesized by the modified solidstate diffusion technique, are reported. In irradiated phosphor

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ExperimentalICDD 41-1473

B.P. Kore et al. / Journal of Luminescence 143 (2013) 337–342338

Na21Mg(SO4)10Cl3:Dy peak consisting of three overlapping (unre-solved) peaks was observed whereas in Na21Mg(SO4)10Cl3:Eusingle peak peaking at 136.5 1C was observed. For the first timethe kinetic parameters of these materials were calculated by peakshape method and the results are presented in this paper.

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(Ar

2 Theta

Fig. 1. X-ray diffraction pattern of the Na21Mg(SO4)10Cl3 host lattice.

2. Experimental

The samples Na21Mg(SO4)10Cl3 (pure); Na21Mg(SO4)10Cl3:Dyand Na21Mg(SO4)10Cl3:Eu were prepared by a modified solid statediffusion method. While preparing the samples, the constituentsNa2SO4(Loba, 99% pure), NaCl(Loba, 99% pure), MgSO4(Loba, 99%pure), Dy2O3(Merck 99.9% pure) and Eu2O3(Merck 99.9% pure)were taken in a stoichiometric ratio and crushed in a mortar pestlefor 1 h. Then this material was heated at 350 1C for 3 h; after 3 hheating the material was again crushed for an hour and finallyheated at 650 1C for 18 h resulting in the compounds of Na21Mg(SO4)10Cl3:Dy and Na21Mg(SO4)10Cl3:Eu in powder form accordingto the following chemical reaction.

Na2SO4+3NaCl+MgSO4-Na21Mg(SO4)10Cl3

The samples were then slowly cooled at room temperature, atcooling rate of 0.5 1C/min. The resultant polycrystalline materialwas crushed to fine powder in a mortar pestle, the resultantpowder formed was used for further study.

SEM micrographs were obtained using a HITACHI S-4800scanning electron microscope. The SEM micrographs were takenat 5000 V accelerating voltage, 8300 μm working distance,7800 nA emission current, at high lens mode with fast scan speedand gray scale color mode. The prepared host lattice was char-acterized for their phase purity and crystallinity by X-ray powderdiffraction (XRD) using a X'pert-PRO PANalytical diffractometer(Cu-Kα radiation) at a scanning step of 0.001, in the 2θ range from10 to 801. The photoluminescence (PL) emission spectra of thesamples were recorded using a Fluorescence spectrometer(Shimadzu, RF 5301 PC). Excitation and emission spectra wererecorded using a spectral slit width of 1.5 nm.

For TL studies, samples were exposed to gamma rays from a60Co source at room temperature at the rate of 0.58 kGy/hr. Afterthe desired exposure, TL glow curves were recorded with the helpof Nucleonix 1009I TL reader, at a heating rate of 5 1C s−1. All themeasurements were carried out in an open atmosphere. TheNucleonix 1009I TL reader consists of photomultiplier tube(931B), DC Amplifier, IR filters and milivolt recorder. For TLmeasurement, each time 5 mg of phosphor is used which is inpowder form, having particle size as specified in Section (3.2). Forcomparison TL glow curve of standard thermoluminescence dosi-meter (TLD) CaSO4:Dy was recorded, under identical conditions.For measurement of dose response and fading three aliquot of thesame sample were used for taking each measurement. Therefore,single point in these plots corresponds to average of threereadings.

3. Results and discussion

3.1. XRD study

Fig. 1 shows the XRD patterns from pure Na21Mg(SO4)10Cl3powder. X-ray diffraction pattern indicates the presence of crystal-line Na21Mg(SO4)10Cl3 host lattices. The XRD-pattern of the asprepared phosphor powder shows good agreement with standardICDD file no. 41-1473.The final product was formed in

homogeneous form, the XRD pattern of Na21Mg(SO4)10Cl3 didnot show the presence of the phases of starting materials likeNa2SO4, NaCl, MgSO4 and other likely phases which indicates theformation of the desired compound. The mineralogical name ofNa21Mg(SO4)10Cl3 is D'ansite. Na21Mg(SO4)10Cl3 has a cubic crystalstructure with space group of I-43m and the cell parameters area¼b¼c¼15.95 Ǻ, V¼4029.55, and Z¼4. It has been found that thecrystal structure of Na21Mg(SO4)10Cl3 is Isometric of class Hexte-trahedral type. Point group: −43m. As tetrahedral {211} crystals,modified by {211} and{110}[19].

3.2. SEM study

The morphology of the Na21Mg(SO4)10Cl3 phosphor was ana-lyzed using SEM as shown in Fig. 2.The SEM micrographs in(a) and (b) shows the agglomerated particles of oval shapes,whereas from micrographs (c) and (d) the spherical agglomeratedparticles can be observed. From SEM observation the estimation ofparticle size is uncertain since the particles are agglomerated;approximately the particle size varies from 0.2 μm to 0.6 μm.

3.3. PL Studies

3.3.1. PL study of Na21Mg(SO4)10Cl3:DyA series of Na21Mg(SO4)10Cl3:Dy samples has been synthesized

with Dy concentration ranging from 0.05 to 1 mol%. Fig. 3 showsthe excitation spectrum in the range 250–400 nm consisting offour peaks, arising due to (6H15/2-

4M17/2), (6H15/2-6P7/2),

(6H15/2-4I11/2) and (6H15/2-

4I13/2) transitions which are locatedat 325 nm, 351 nm, 365 nm, 388 nm respectively. The photolumi-nescence emission spectra of Dy3+ doped Na21Mg(SO4)10Cl3:Dysample under excitation at 351 nm is shown in Fig. 4. The emissionspectrum of Dy3+ has two groups of emissions located at 482 and576 nm, which correspond to the transitions of 4F9/2-6H15/2

(blue), 4F9/2-6H13/2 (yellow) respectively. Among the two emis-sion peaks, the 4F9/2-6H13/2 emission belongs to hypersensitivetransition with ΔJ¼2, which is strongly influenced by outsideenvironments of Dy3+ [20]. In the excitation spectrum of 1 mol%Dy3+ doped Na21Mg(SO4)10Cl3, the peaks which range from 250 to400 nm are due to 4f–4f transitions of Dy3+ [21]. For the lowerconcentration of Dy there is no photoluminescence observed.

3.3.2. PL study of Na21Mg(SO4)10Cl3:EuThe PL spectra of Na21Mg(SO4)10Cl3:Eu (x¼0.2 mol%, 0.5 mol%,

and 1 mol%) phosphors are presented in Fig. 5, monitored at 370 nm(as shown in inset of Fig. 5.). It can be seen that the phosphors exhibita broad blue emission band with a peak at around 450 nm, which iscorresponding to the 5d-4f allowed transition of Eu2+. From thespectra it is clear that the PL intensity increases with increasing Eu2+

Fig. 2. SEM micrographs of Na21Mg(SO4)10Cl3 phosphor.

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Fig. 3. Excitation spectra of Na21Mg(SO4)10Cl3:Dy monitored at 482 nm.

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Fig. 4. Emission spectra of Na21Mg(SO4)10Cl3:Dy at λex¼351 nm.

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Fig. 5. Emission spectra of Na21Mg(SO4)10Cl3:Eu at λex¼370 nm.

B.P. Kore et al. / Journal of Luminescence 143 (2013) 337–342 339

concentration and reaches the maximum at x¼1 mol% concentra-tion. We suggest that Eu2+ ions will preferably substitute Mg2+ sitesin Na21Mg(SO4)10Cl3, since the ions' charge, radius of activator ionsand cations in the host are in close proximity.

3.4. TL Studies

3.4.1. Na21Mg(SO4)10Cl3:DyThermoluminescence is a very common and simple technique

used for estimation of doses of high-energy ionizing radiationsabsorbed by materials. As-prepared Na21Mg(SO4)10Cl3 samples, didnot show any thermoluminescence response. However, samplesirradiated with gamma rays shows good TL response. Fig. 6 showsa glow curve for the sample exposed by gamma rays. The TL glowcurves of Na21Mg(SO4)10Cl3:Dy compound show unresolved glowpeak, consisting of two peaks, indicating that three types of trapsare being activated within the particular temperature range withits own value of activation energy (E) and frequency factor (s). The

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a

Fig. 6. TL glow curve of Na21Mg(SO4)10Cl3:Dy phosphor (at gamma ray exposure of6 Gy).

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Fig. 7. TL glow curve of Na21Mg(SO4)10Cl3:Eu phosphor (at gamma ray exposure of6 Gy).

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Fig. 8. TL response of microcrystalline Na21Mg(SO4)10Cl3:Dy exposed to γ-rays inthe dose range 100 mGy–12 Gy.

B.P. Kore et al. / Journal of Luminescence 143 (2013) 337–342340

shape of the glow curve remains almost the same for differentconcentrations of Dy3+ but the height of the glow peak is raising.The sensitivity of main glow peak is raising. with increase ofconcentrations of doped Dy3+ ion in Na21Mg(SO4)10Cl3. Theincrease in glow peak sensitivity is linear upto 1 mol% concentra-tion of Dy3+ (the maximum concentration used in this study) andthis will be favorable for TL studies. The increase in the intensitiesof the glow peaks with increase of dopant concentration can beunderstood by the fact that more and more defects were created.Therefore, we can conclude that the distributions of traps pro-duced by the irradiation of gamma-ray can be altered greatly bythe change in the concentrations of Dy3+ ion doped in Na21Mg(SO4)10Cl3 phosphor. Studies on the TL glow curves of Na21Mg(SO4)10Cl3 samples doped individually with different rare earthimpurities show that the peak temperature and the activationenergies of the glow peaks are depend on the type of activatorpresent in phosphor. In comparison to dosimetric peak of CaSO4:Dy (220 1C), Na21Mg(SO4)10Cl3:Dy is found to be 1.23 times moresensitive.

3.4.2. Na21Mg(SO4)10Cl3:EuFig. 7 shows the glow curve for a sample of Na21Mg(SO4)10Cl3:

Eu, exposed to 6 Gy dose of γ-rays. For the investigation of thevariation in glow curves on dopant concentration, the TL signalsfor different Eu concentrations were measured and are repre-sented in Fig. 7. The Eu concentrations in Na21Mg(SO4)10Cl3:Euused were 0.05, 0.1, 0.2, 0.5 and 1 mol%. The maximum TL intensityis observed for 0.1 mol% concentration of Eu, peaking at 136.5 1Cand further increase in Eu concentration ceases the luminescence;this is due to concentration quenching. The TL glow curves ofNa21Mg(SO4)10Cl3:Eu compound show single glow peak peaking at136.5 1C indicating that only one set of traps are being activatedwithin the particular temperature range having its own value ofactivation energy (E) and frequency factor (s). In comparison todosimetric peak of CaSO4:Dy our prepared material that is Na21Mg(SO4)10Cl3:Eu is found to be 4 times less sensitive and moresensitivity than CaSO4:Dy is observed for Na21Mg(SO4)10Cl3:Dyphosphor.

3.5. Linearity, fading and reusability

The TL intensity of glow peak increases linearly with variationin the dose from 100 mGy to 10 Gy and is shown in Fig. 8. Theincrease in the intensities of the glow peaks with increase of

radiation dose suggests that more and more traps, responsible forthese glow peaks, were getting filled with the increase of radiationdose and subsequently these traps releases the charge carriers onthermal stimulation, to finally recombine with their counterparts,thus giving rise to glow peaks of different intensities. The TL glowcurves show good response upto 10 Gy and above this exposurethe TL peak intensity is going in saturation stage. The preparedphosphor Na21Mg(SO4)10Cl3:Dy is useful for TL dosimetry upto8 Gy dose of gamma exposure.

In order to make samples useful in radiation dosimetry their TLshould be stable and should not die away upon storage afterexposure to ionizing radiations. The present material was storedfor a few days without taking any protection to shield it from lightand humidity and it was found that glow peak was reasonablystable as shown in Fig. 9. The fading observed was about 8 to 10%during a period of 30 days indicating no severe fading.

Reusability is one of the most useful property that sampleshould posses in order to find a place in any application. If thesensitivity of a sample does not change after several cycles ofexposures and readouts then it is termed as a phosphor with gooddosimetric characteristics. For studying the reusability of thesample, sample was given exposure of 6 Gy of γ-rays and TL glowcurve was recorded. Several such cycles of exposures and glowcurve recordings were executed. The plot between TL readout

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Fig. 9. Fading of microcrystalline Na21Mg(SO4)10Cl3:Dy.

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Fig. 10. Reusability of microcrystalline Na21Mg(SO4)10Cl3:Dy.

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Fig. 11. Tm–Tstop plot for thermoluminescence glow curve of Na21Mg(SO4)10Cl3:Dy(Dy¼1 mol%) phosphor.

B.P. Kore et al. / Journal of Luminescence 143 (2013) 337–342 341

cycles and TL sensitivities is shown in Fig. 10. No significant changein the sensitivity of the glow peak was observed, as observed inFig. 10.

Several methods [22–25] for determining kinetic parameters ofTL phosphors require the values of Tm, T1 and T2. The determina-tion of trapping parameters from the thermoluminescence glowcurves of Na21Mg(SO4)10Cl3:Dy and Na21Mg(SO4)10Cl3:Eu isgiven below.

3.6. Analysis of TL glow curve and calculations of kinetic parameters

3.6.1. Tm–Tstop procedure for determining peak positionsThe broad nature of the recorded glow curves may be attrib-

uted to the overlap of various peaks having a continuous distribu-tion of their trap depths. It is well known that the broad TL peaksmay be resolved using glow curve deconvolution (GCD) mathe-matical functions based upon various TL models. In this study toextract the information about positions of various constituentglow peaks the Tm–Tstop method was employed. Tm–Tstop methodhelps to separate the overlapping peaks and to determine Tm valuefor each of them. The flat regions in the Tm–Tstop plot indicateposition of the peaks in complex glow curve. The method consistsin heating at a linear rate a pre-irradiated sample, to sometemperature Tstop. The sample is then quenched to room tempera-ture and then reheated in order to record the entire remainingglow curve. The process is repeated several times with samequenched/pre-irradiated sample at different Tstop values.

In the present case, at a time 18 samples were exposed to the γdose of 5 Gy and each sample was quenched at different Tstoptemperatures from 100 1C to 270 1C then the TL curves wererecorded with a linear heating rate of 5 1C s−1. In this sample, therise from one plateau region to another is fairly sharp, as observedin Fig. 11. The plot indicates the presence of only two flat regionsas the Tstop is increased, however this increase is not monotonicand two jumps are observed, indicating the presence of 2 peaks.On the basis of the results of this analysis it seems apparent thatthe TL glow curve is due to a complex trap structure, namely adiscrete trap distribution. In addition to Tm–Tstop method, all theglow curves were also analyzed by CGCD method to obtain thenumber of glow peaks. This method has become very popular toobtain the number of glow peaks in the complex glow curves andtheir kinetic parameters.

3.6.2. Glow curve deconvolution (CGCD)For determination of nature of TL process computerized glow

curve fitting methods have been used and these methods werefound to be very helpful in understanding advances in TL mechan-ism. In this study the glow curve convolution deconvolution(GCCD) curve fitting in Na21Mg(SO4)10Cl3:Dy material was done.The order of kinetics and activation energy of the isolated peakwere found using Chen's set of empirical formulae [26,27]. Todetermine the general order of kinetics (other than first or secondorder), use of the correlation between order of kinetics (b) and theform factor (μg) given by Chen was made [28,29]. Once E and b areknown, s can be evaluated by Chen and Kirsh [30]. In first-orderkinetics it is assumed that there is no such retrapping of chargeswhereas in second-order kinetics retrapping of charges occurs[28]. Trap depth or the thermal activation energy (E) was againcalculated using the set of equations given by Chen. This procedurewas repeated for all the TL peaks till a theoretical glow curve wasobtained by their convolution to overlap with experimental glowcurve. Some authors have reported evaluation of kinetic para-meters using Chen's peak method applied directly to the peaks,which were deconvoluted using the origin 6.1 software withoutusing any Glow Curve Deconvolution (GCD) function [31,32].

Fig. 12 shows the experimental glow curve for Na21Mg(SO4)10Cl3:Dy (Dy¼1 mol% doped) at heating rate of 5 1C s−1, which has beendeconvoluted into two peaks using GCD function. Tm–Tstop methodconfirmed that experimental glow curve consisting of only two peakswhich attributes to two types of traps. Fig. 12 illustrates closeresemblance between experimental and theoretical glow curve

Table 1Kinetic parameters using the GCD function.

Sample Peakno

Tm(1C) Symmetryfactor (μg)

Order ofkinetics

ActivationEnergy, E(eV)

Frequencyfactor s (s−1)

Na21Mg(SO4)10-Cl3:Dy

1 151.4 0.5032 1.9 0.9767 1.2494�1011

2 192.5 0.4908 1.8 1.2292 6.39�1012

Na21Mg(SO4)10-Cl3:Eu

1 136.5 0.52 2 0.7181 6.245�108

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Fig. 12. Deconvoluted glow curve of Na21Mg(SO4)10Cl3:Dy.

B.P. Kore et al. / Journal of Luminescence 143 (2013) 337–342342

obtained by GCD function. The position of respective peaks, trapparameters and order of kinetics are shown in Table 1. When thetrapped electrons make transition to the conduction band by thethermal energy, they have two kinds of chances to make transitiontoward lower energy side. One is the retrapping process returning tothe same kind of traps and another is the recombination with thehole accompanied by the emission of TL light. If the probability ofbeing re-trapped is negligible then probability of rapid recombinationprocess increases and glow curve has a narrow peak shape. Instead, ifthe retrapping dominates, the recombination with the holes issuppressed and the glow curve has a wide peak. These two descrip-tions are called the first order kinetics and the second order kineticsphenomena. Between these two types, the general order kinetics isintroduced for providing a proper analytic continuation from thediscrete two types of kinetics. The isolated peaks were analyzed withthe help of Chen's peak shape method [33] to evaluate the peakparameters, using the values of the parameters Tm, T1 and T2 from thedeconvoluted TL glow curves, as shown in Fig. 12. The geometricalform factor for the phosphor Na21Mg(SO4)10Cl3:Dy is calculated to beequal to 0.5032 for first peak at 151.4 1C, 0.4908 for second peak at192.5 1C and 0.4838 indicating general-order kinetics having b values1.9 and 1.8 respectively. For Na21Mg(SO4)10Cl3:Eu the peak obeysecond order kinetics having μg¼0.52 which illustrates retrappingof charges in the phosphor [23]. Trapping parameters of all the peaksare summarized in Table 1.

4. Conclusion

Comparison with data concerning undoped and Dy-dopedNa21Mg(SO4)10Cl3 allows for identification of the contributions ofimpurities to the glow curves. The TL glow curve of Na21Mg(SO4)10Cl3:Dy shows a complex structure of glow curve whereasin case of Na21Mg(SO4)10Cl3:Eu simple glow curve is observed. This

complex nature of glow curve in Na21Mg(SO4)10Cl3:Dy is resolvedby deconvolution and these deconvoluted glow curves are attrib-uted to two types of traps. The Tm–Tstop procedure indicates thatthe position of dosimetric peak shifts slightly toward the hightemperature side with increasing Tstop. These results imply thatthe dosimetric peak of Na21Mg(SO4)10Cl3:Dy after γ-irradiation canbe best described as a superposition of glow peaks. Table 1 givesthe values of trapping parameters of glow peaks of Na21Mg(SO4)10Cl3:Dy and Na21Mg(SO4)10Cl3:Eu phosphors calculated byChen's peak shape methods. The γ dose response of this peak islinear in the dose range 100 mGy–8 Gy. The post-irradiation fadingof this peak at room temperature is also less than 10% in onemonth. At present days, there is a great demand of the dosimetricphosphors which exhibit simple and sharp glow curves. Thecompound Na21Mg(SO4)10Cl3:Eu has been found to have simpleand sharp glow peak and moreover it can be prepared very easily.Na21Mg(SO4)10Cl3:Dy has more sensitivity than CaSO4:Dy. Furtherwork is in progress to clarify details of the defect within thematerial and glow curve structure.

Acknowledgement

Authors (BPK, NSD and SJD) are grateful to the Board ofResearch in Nuclear Sciences (BRNS), Department of atomicEnergy, Govt. of India, for providing financial assistance to carryout this work under research project (sanctioned letter No. 2011/37P/10/BRNS/144).

References

[1] A. Bravim, R.K. Sakuraba, J.C. Cruz, L.L. Campos, Radiat. Meas. 46 (2011) 1979.[2] T. Rivera, J. Roman, J. Azorín, R. Sosa, J. Guzmán, A.K. Serrano, M. García,

G. Alarcán, Appl. Radiat. Isot. 68 (2010) 623.[3] T. Rivera, Appl. Radiat. Isot. 71 (2012) 30.[4] W. Saitoa, I. Ikejima, Y. Fukuda, Y. Momoi, Radiat. Meas., 46, 286.[5] C. Furetta, A. Favalli, E. Cruz Zaragoza, J.M. Gomez-Ros, G. Kitis, Radiat. Eff.

Defects Solids 162 (2007) 751.[6] M.T. Jose, S.R. Anishia, O. Annalakshmi, V. Ramasamy, Radiat. Meas. 46 (2011)

1026.[7] M. Klosowski, L. Czopyk, K. Kisielewicz, D. Kabat, P. Olko, M.P.R. Waligo’rski,

Radiat. Meas. (2010)719.[8] L. Daling, Z. Chunxiang, D. Zouping, L. Guozhen, Radiat. Meas. 30 (1999) 59.[9] J. Harvey, N. Haverland, K. Kearfott, Appl. Radiat. Isot. 68 (2010) 1988.[10] A.M. Muke, P.L. Muthal, S.M. Dhopte, S.V. Moharil, J. Lumin. 132 (2012) 342.[11] J. Sun, R. Sun, H. Du, J. Alloys Compd. 516 (2012) 201.[12] E. Tekin (Ekdal), A. Ege, T. Karali, P.D. Townsend, M. Prokić, Radiat. Meas. 45

(2010) 764.[13] J. Kim, J. Lee, S. Chang, K. Chung, H. Choe, Radiat. Meas. 38 (2004) 435.[14] A. Choubey, S. Das, S. Sharma, J. Manam, Mater. Chem. Phys. 120 (2010) 472.[15] D. Junot, D. Vasconcelos, M. Chagas, M. Santos, L. Caldas, D. Souza, Radiat.

Meas. 46 (2011) 1500.[16] P. Sahare, S. Moharil, J. Phys. D: Appl. Phys. 23 (1990) 567.[17] S. Gedam, S. Dhoble, S. Moharil, J. Lumin. 124 (2007) 120.[18] V. Pagonis, G. Kitis, C. Furetta, Numerical and Practical Exercises in Thermo-

luminescence, Springer, USA, 2006.[19] ⟨http://www.handbookofmineralogy.org/pdfs/dansite.pdf⟩.[20] H. Choi, C. Kim, C. Pyun, S. Kim, J. Lumin. 82 (1999) 25.[21] J. Kuang, Y. Liu, J. Zhang, J. Solid State Chem. 179 (2006) 266.[22] L. Jiang, Y. Zhang, C. Li, J. Hao, Q. Su, Appl. Radiat. Isot. 68 (2010) 196.[23] G. Kitis, J. Ros, J. Tuyn, J. Phys. D: Appl. Phys. 31 (1998) 2636.[24] C. Furetta, G. Kitis, C.-H. Kuo, Nucl. Instrum. Methods Phys. Res. B 160 (2000)

65.[25] A. Yazici, M. Haciibrahimoglu, M. Bedir, J. Phys. 24 (2000) 623.[26] S. Singh, S. Lochab, R. Kumar, N. Singh, Physica B 406 (2011) 177.[27] M. Jose, S. Anishia, O. Annalakshmi, V. Ramasamy, Radiat. Meas., 46, 1026.[28] A. Pandey, V. Sharma, D. Mohan, R. Kale, P. Sahare, J. Phys. D: Appl. Phys.

35 (2002) 1330.[29] S.W.S. McKeever, Thermoluminescence of Solids, Cambridge University Press,

London, 1983.[30] R. Chen, Y. Krish, Analysis of Thermal Stimulated Process, Pergamon

New York, 1981.[31] K. Nagabhushana, B. Lakshminarasappa, Fouran Singh, Radiat. Meas.

43 (2008) S651.[32] S. Singh, A. Vij, S. Lochab, R. Kumar, N. Singh, Bull. Mater. Sci. 34 (2011) 683.[33] R. Chen, J. Appl. Phys. 40 (1969) 570–585.