Thermoluminescence kinetic analysis and dosimetry features of MgSO4:Dy and MgSO4:Cu nano-rods

Author’s Accepted Manuscript Thermoluminescence kinetic analysis and dosimetry features of MgSO4:Dy and MgSO4:Cu nano-rods M. Zahedifar, F. Almasifard, E. Sadeghi, M. Kashefi Biroon, A. Ramazani- Moghaddam-Arani www.elsevier.com/locate/radphyschem

PII: DOI: Reference:

S0969-806X(16)30115-3 http://dx.doi.org/10.1016/j.radphyschem.2016.04.005 RPC7119

To appear in: Radiation Physics and Chemistry Received date: 16 January 2016 Revised date: 16 March 2016 Accepted date: 7 April 2016 Cite this article as: M. Zahedifar, F. Almasifard, E. Sadeghi, M. Kashefi Biroon and A. Ramazani- Moghaddam-Arani, Thermoluminescence kinetic analysis and dosimetry features of MgSO4:Dy and MgSO4:Cu nano-rods, Radiation Physics and Chemistry, http://dx.doi.org/10.1016/j.radphyschem.2016.04.005 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 galley proof before it is published in its final citable 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.

Thermoluminescence kinetic analysis and dosimetry features of MgSO4:Dy and MgSO4:Cu nano-rods M. Zahedifar1,2*, F. Almasifard1, E. Sadeghi1,2, M. Kashefi Biroon1, A. Ramazani- Moghaddam-Arani1 1

2

Physics Department, University of Kashan, Kashan, I.R.Iran

Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan, I.R.Iran

*Corresponding author at: Physics Department, University of Kashan, Kashan, I.R.Iran. Tel.: +98 31 55912577; fax: +98 31 55912570. E-mail address: [email protected] (M. Zahedifar).

Abstract MgSO4:Dy and MgSO4:Cu nano-rods (NRs) were synthesized for the first time by semi co- precipitation method. X- ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were utilized for sample characterization. The optimum amount of dysprosium and copper concentrations were obtained both at 0.1 mol% in MgSO4:Dy and MgSO4:Cu NRs. Tm-Tstop and computerized glow curve deconvolution (CGCD) methods were used for identifying the number of component glow peaks and kinetic parameters of the synthesized NRs. Initial rise and variable heating rate methods were also used to ensure the reliability of obtained kinetic parameters. Results show that the TL sensitivity of MgSO4:Dy is about 7 times more than that of magnesium sulfate doped with Cu. The TL dose response of MgSO4:Dy and MgSO4:Cu NRs are linear up to absorbed dose of 10 KGy. Other TL dosimetry characteristics of the produced NRs are also presented and discussed. Keywords: Thermoluminescence, MgSO4:Dy, MgSO4:Cu, Nano-rod, Dosimetry, Kinetic parameters

1. Introduction TL is a luminescence phenomenon that happens in insulator or semiconductor materials previously exposed to ionizing radiation. This phenomenon occurs when the solid is stimulated by thermal energy (heat) (Bos, 2007; Kher et al, 2011). TL has been used in different areas of dosimetry, like environmental, personal, and medical.

1

The characteristics of known TL materials have been improved for dosimetry applications; they have different commercial names (McKeever, 1985). Recently, sulfates have attracted the attention of researchers because of their applicability in radiation dosimetry. For example, CaSO4 is known as radiation dosimetry material because of its high TL sensitivity (Salah, 2015; Zahedifar et al, 2011). Another phosphor is MgSO4 which is recognized as a good material for TL dosimetry. Sensitivity of a TL material is an important factor to be a good radiation dosimeter. Some works (processes) can improve this factor like adding an impurity, irradiation at certain dose, and proper thermal treatment (Gonzalez et al, 2013). So, in recent works,MgSO4 with different dopants like Dy,Mn, Eu, Tm, and co-dopants like Dy,Mn, and Dy,Mn,P have been studied (Luo et al, 2006; Luo et al, 1999; Zhang et al, 2002; Zhang and Luo, 2002; Zhang et al, 2000). In the MgSO4:Dy bulk sample, four glow peaks were observed at 140, 190, 260, 360ºC (Zhang et al, 2001). In another research, it was found that the TL glow peak of MgSO4:Dy contains 2 peaks at 110 and 220 ºC and also by increasing the concentration of impurity, one peak at 150 ºC was appeared (Kher et al, 2008). Recently, researchers have paid wide attention to the nano-scaled materials because of their outstanding characteristics. It has been established that the properties of nano-scaled materials changes with variation in their size (Holmes et al, 2000; Huang et al, 2001). With decreasing the particle size, the ratio of surface to volume is increased, the result of this fact is growth of specific active sites for chemical reactions and photon absorptions. Another effect of size reduction is change in the optical properties due toincrease in band gap (Kumbhakar et al, 2008). It has been found that nanophosphors are so suitable for measuring high dose radiation, where most of the microcrystalline TLD phosphors saturate (Pandey et al, 2010;Salah et al, 2006). Lately, many research works have been published on TL properties of nano materials (Brahmea et al, 2012;Chen et al, 2011; Prashantha et al, 2011; Zahedifar et al, 2012; Zahedifar and Sadeghi, 2013; Zahedifar et al, 2011).Considering the proper TL dosimetry features of the bulk MgSO4 phosphors, the TL characteristics of its nano-scale counterpart is investigated in this work. MgSO4:Dy and MgSO4:Cu NRs were synthesized for the first time by the novel semi co-precipitation method which is explained in the next section and their TL kinetic parameters and dosimetry features is presented and discussed.

2

2. Sample preparation After preparing all the raw materials from the Merk Chemicals, MgSO4:M [M = Dy,Cu] nanostructures were synthesized according to the following procedure:0.3024g of Mg(NO3)2.6H2O(99.99% purity) was dissolved

in

10

cc

ethanol(99.99%

purity)

(solution

A),

0.0025g

(=

0.5mol%)

of

Dy(NO3)3[Cu(NO3)2](99.99% purity) was dissolved as dopant in15M hydrochloric acid(solution B). For different concentrations of impurity, different amounts of Dy (NO3)3[Cu(NO3)2]was used. Solution B was added to solution A and was stirred for 15 minutes (solution C).0.1546g of (NH4)2SO4(99.99% purity) was dissolved in 10cc ethanol and deionized water and was added to the solution C drop wise while it was stirred. Subsequently, the resultant transparent solution was put in an oven at 90οC for 12 hours. The final product MgSO4:Dy [MgSO4:Cu] is soluble in water. On the other hand the usage of water is essential in the synthesis procedure since the precursor (NH4)2SO4 is solved exclusively in water. Therefore the precipitate is observed after evaporating the solvents of water and ethanol, so the semi- co precipitation method.Then the precipitate was washed for 5-6 times with ethanol and was dried for 2 hours at 90 οC in the oven. Finally, the produced white powder was put in a furnace for a two stage annealing program: first in 500˚C for one hour, followed by an ultra heating at 600˚C for one hour. By using this procedure, the produced nanoparticles are so tiny and sticking together. Therefore, another surfactant (PVP) was used and the above mentioned reaction was repeated using ultrasound wave which resulted in nano-rods. All the following analyses were done using the NRs produced by means of ultrasonic method.

3. Experimental method The structure of the synthesized NRs was confirmed by taking X-ray diffraction (XRD) pattern using a Rigaku D-maxIII diffractometer (BrukerD8 Advance) with CuKα(λ= 1.54˚ A) radiation under the conditions of 40 kV and 30 mA, at a step size of 2θ = 0.02ο. A scanning electron microscope model Philips XL-30 ESEM equipped with energy dispersive spectrometer (EDS) was used to identify the shape and size of the produced NRs and its elemental concentrations. The mass of samples for different tests were fixed at 0.004 ± 0.0001 g by using a SHIMADZU Ax120 (max = 120g, d = 0.1 mg). All irradiations were made using a 60Co gamma source. The TL readouts were taken in a Harshaw model 4500 computerbased TL reader using a contact heating where the temperature of the heater strip (planchet) is recorded as 3

indicator of the temperature of the sample with a precision of 1K . The heating rate for readout was 2K/s (with preheat of 323K) to a maximum temperature of 623K. All the samples were heated and annealed in a programmable oven with temperature precision of 1K and then were cooled rapidly to room temperature (75 K/min).

4. Results and Discussion The TL sensitivity depends critically on the kind and concentration of impurity. For optimizing the impurity concentration, different amounts of Dy and Cu were added to the MgSO4 and their effect on TL sensitivity was examined. In Fig.1 (a) and (b),the TL sensitivities are shown for different Dy and Cu concentrations. It is observed that the optimum concentration in both cases is at 0.1mol% of the impurity which is the same as reported optimum concentration for Dy impurity in microcrystalline MgSO4 (Luo et al, 1999; Zhang et al, 2000). In Fig. 2, the XRD pattern of MgSO4 is shown. This pattern shows an orthorhombic structure that is in correspondence with ICSD collection code no 74-1364. SEM image is shown in Fig.3 (a) and (b). As is seen in Fig. 3(a), without using ultrasound wave during the production process, the nanoparticles are sticking to form bulk material. Upon using ultrasound, the nano-rods with square shape cross-sections were formed (Fig.3 (b)) and utilized in this research work. EDS, analysis was carried out for identifying the Dy and Cu concentration in MgSO4 host material. The results are shown in the figure 4 (a) and (b) which reveals the formation of MgSO4:Cu and MgSO4:Mn without contamination. For confirmation of the impurity improvement effect, a comparison of TL glow curves among pure MgSO4 NRs and MgSO4:M [ M=Dy, Cu= 0.1 mol% ] NRs for the same administrated dose of 10Gy is shown in Fig.5. Manam and Dos in their study on TL characteristics of Cu and Mn doped MgSO4 bulk material showed that the intrinsic defects in the host material are responsible for the trapping states. Incorporating the impurity which acts as activator, increases the intensity of the TL glow peak. They also found that the Cu doped MgSO4 has lesser TL sensitivity than Mn doped material. Changing the glow curve structure of the doped sample indicates that there are interactions between intrinsic defects and doped impurities. They also revealed that the TL glow curves of X-irradiating Cu doped MgSO4 exhibit a main glow peak at 176 ºC. Because of high surface to volume ratio in nanostructured counterpart of Cu doped MgSO4 and importance of surface defects in nanostructures which have different trapping 4

parameters than the volume defects, it is expected that the TL glow curve of Cu doped MgSO 4 NRDs in Fig. 5 to be different from its bulk equivalent. Comparison of TL glow curves of MgSO4 in Fig.5 with and without dopants, demonstrates that adding impurity into the MgSO4 host material, highly increases the TL intensity. Also, the TL response of MgSO4:Cu is about 7 times smaller than that of MgSO4:Dy NRs. It has been suggested that the glow curve of Cu doped MgSO4 is related to the relaxation of the excited Cu+ ions (Manam and Dos, 2010), while the TL emissions in MgSO4:Dy are characteristics of transitions between the states of Dy3+ and this ion acts as the luminescence center in MgSO4 phosphor (Pradhan et al, 1984). If the glow curve structure of undoped sample is changed after the doping, it indicates that there are interactions between intrinsic defects and doped impurities. In our results, both the Cu and Dy impurities enhance the TL sensitivity, however incorporating Dy in the host material results in more TL output. In a similar behaviors of Cu and Dy impurities, it has been observed that Cu doped CaF2 nanoparticles show lower TL sensitivity than Dy doped CaF2 nanoparticles.( Zahedifar et al, 2012; Zahedifar and Sadeghi, 3013).Moreover, the TL intensity of synthesized MgSO4:Dy NRs is a little more than that of bulk MgSO4:Dy phosphor. This is a remarkable result in view of the fact that the most of TL materials in nano-scale have TL sensitivities lower than those of microcrystalline counterparts and at the same time they show linear dose response up to high dose levels, where their microcrystalline equivalents are saturated (Salah, 2015;Salah et al, 2006;Zahedifar et al, 2012; Zahedifar and Sadeghi, 2013). TL dose response of the synthesized MgSO4:Dy and MgSO4:Cu NRs are shown in Fig.6(a) and (b) respectively. A linear dose response up to the absorbed dose of 104 Gy is observed for both NRs, while the bulk MgSO4does not show a linear dose response at low dose levels and it saturates at received doses higher than about 500 Gy (Upadhyay et al, 2011). The reusability is an important aspect for a proper TL dosimeter. For examining this factor, seven samples of each MgSO4:Dy and MgSO4:CuNRs were subjected to the cycles of annealing, irradiation to 100 Gy gamma dose and readout for 10 times. No significant change in TL response was observed after 10 above-mentioned cycles. As the stored TL signal in irradiation process directly relates to the absorbed dose, it is important to examine the fading of the stored TL signal by keeping the samples at room temperature. Two main bumps are evident in the TL glow curve of MgSO4:Dy and MgSO4:Cu NRs which we refer to them as main peak 1 and main peak 2. Figure 7(a) and (b) shows respectively the fading of TL signal for MgSO4:Dy and MgSO4:Cu NRs. It can be observed in part (a) that the main peak 1(including glow peaks 1 and 2) is 5

approximately disappears following keeping the sample in dark place at room temperature for 5 weeks., but in the case of main peak 2 (including glow peaks 3+4), the TL response remains almost constant after 2 weeks. The reduction percentages for main peaks1and 2 following a storage time of 1 month are about 77.43% and 55.67% respectively, also this value for total glow curve area of MgSO4:Dy is about 66.94%. In Fig.7(b) it is observed that the decrease in the area of main peak 1(including glow peaks 1+2) is so much and fast, such that it approximately disappears after 30 day. The reduction percentage of this peak after 30 days is about 48.8%. The area of main peak 2 (glow peaks 3+4+5) is also decreased, but it is so lesser and smoother and its decrease percentage after 30 days storage at room temperature is 15.21%. The total reduction percentage of glow curve area of Cu doped MgSO4 NRs glow curve is about 36.8%.

4.1 TL kinetics analysis To study the TL characteristics of a certain material, it is necessary to determine a suitable annealing program. A proper thermal treatment can improve the TL sensitivity, so the first step is choosing the best procedure for annealing. For this purpose, different annealing programs were tested. Amongst these programs 500 οC – 15 min was the best. All of anneals were done in a furnace in air. Glow curve was deconvoluted using the computerized deconvolution program which has been produced in our laboratory using Levenberg-Marquart algorithm, based on least square method. This program uses general order kinetics, mixed order kinetics and also complex functions describing continuous trap distribution to parameterize the shape of the glow peaks. In this work, general order of kinetics was used to obtain the parameters of the deconvoluted glow peaks. The solution of the general order kinetics equation in terms of intensity and temperature of the peak maximum is given by (Kitis et al, 1998): b

æ E (T - Tm ) ö ÷ I (T ) = I m b b-1 exp ç ÷´ ç kTTm ø è ì 2kTm E (T - Tm ) 2kT ïT (b - 1)(1 ) exp ( ) + 1 + (b - 1) í 2 E kTTm E ï îTm 2

where  is the maximum peak intensity,

 the

maximum temperature,

-b ü b-1

(1)

ï ý ï þ

the absolute temperature, ! the

activation energy, " the Boltzmann’s constant and # the kinetic order. To test the correctness of fitting, the figure of merit (FOM) has been used (Balian and Eddy, 1977): 6

. %&&['( )'(+( )] -

FOM = ∑./0

(2)

in which 12 and 13 are the numbers of the first and last temperature interval Δ used for curve fitting, 45 is the intensity in the 6th interval obtained from experiment and 4(75 ) the intensity expected from Eq(1). FOM values lower than 2.5% show that the theoretical and experimental results are good fitted to each other.

4.2 Tm – Tstop method For identifying the number of glow peaks contained in the main glow peaks, the Tm – Tstop method was employed. For doing that, the irradiated sample (here the dose of irradiation was 1000 Gy) was first heated in TLD reader with the heating rate of 5 K/s to the temperature Tstop, then were cooled to room

temperature without emerging the sample from the reader, followed by recording the glow curve with heating rate of 2 K/s to obtain the peak temperature Tm. This procedure was repeated for the Tstop values between 363-623 K with the step size of 10K and the corresponding Tm values were obtained. By obtaining the Tm values from the above procedure, variation of Tm against Tstop was recorded as Fig. 8 (a, b) respectively for MgSO4:Dy and MgSO4: Cu NRs. As is seen in Fig. 8, the peak temperature Tm increases with Tstop, but this increase is not monotonic and several jumps are evident. Each plateau region in Tm-Tstop plot corresponds to a single glow peak. The plateaus with lower slopes indicate that the glow peak behaves as near first-order kinetics and higher slopes correspond to higher values for the order of kinetics (McKeever, 1985).

4.3 Kinetic parameters By identifying the number of glow peaks from Tm-Tstop plots for MgSO4:Dy and MgSO4: Cu NRs, they ware used along with the Tm and Im values which were estimated from the TL glow curve, as input parameters in CGCD procedure. The results of deconvolution process are shown in Fig 9(a,b) for MgSO4:Dy and MgSO4: Cu NRs. The peak temperatures for MgSO4:Dy are at 416, 436, 489, 550K, and, those for MgSO4:Cu at 407, 430, 478, 520, 553K. Other kinetic parameters of the synthesized NRs obtained from CGCD procedure are shown in Table 1 (a) and (b) respectively for Dy and Cu doped NRs.

7

It is worth noting that the number of glow peaks in MgSO4:Dy NRs is the same as that of MgSO4:Dy bulk material, and also their glow peak temperatures are close to each other (Zhang et al, 2001). The validity of the obtained values for activation energies were checked by measuring them via initial rise and variable heating rate methods. It has been verified that when the heating rate of the sample changes, peak height and temperature will change, so based on this fact, different methods are derived. One of : 89 ;

them is various heating rate method in which, for the first order kinetics, ln

%

is plotted versus8 for 9

different heating rates according to the equation: : 89 ;

ln

< =>

= ln

Where



+

< ?89

(3)

is the peak temperature, β the heating rate, E the activation energy, k the Boltzman`s constant

and s the frequency factor. The result is a straight line with the slop

< . =

The advantage of this method is

that it needs only the peak maximum temperature to be read from the glow curve. In the case of an intense glow peak surrounded by low intensity satellites, the peak temperature can be determined accurately and the thermal quenching does not affect the obtained activation energy (McKeever, 1985). However, determining the activation energies of low intensity glow peaks is a difficult task when the above method is used. Therefore, this method was applied to the lower temperature glow peaks of MgSO4:Dy and MgSO4: Cu NRs which have higher intensity and behave near first order of kinetics. The results are shown in Table 2, which are in accordance with those obtained from CGCD method. The initial rise method was also used to determine the activation energies. In the initial rise part of the glow peak, the TL )<

%

intensity is proportional to exp ( ?8 ). So, plotting lnI versus 8 leads to a straight line with slope of

)< , =

from

which the activation energy can be calculated. The above condition is fulfilled only for initial rise part of the glow peak. Therefore, the highest peak intensity used to obtain lnI was about 10% of the maximum peak intensity and corrections were made due to employing higher intensity points (Singh et al, 1988). In Fig.10 (a) , (b) the plots of lnI versus

% 8

for different separated peaks of MgSO4:Dy and MgSO4:Cu NRs

are drawn. Thermal bleaching was applied to record the initial rise part of each glow peak. The comparative results of three different methods are shown in Table 2 (a) and (b) for MgSO4:Dy and MgSO4:Cu NRs. As it is clear, a good harmony exists between them, indicating the reliability of the obtained results for kinetic parameters. 8

Conclusion MgSO4:Dy and MgSO4:Cu NRs were synthesized for the first time. The XRD, EDS and SEM analysis were carried out and their results confirmed each other very good. Optimum concentration for both Dy and Cu impurities was found at 0.1 mol%. The remarkable result obtained is that while the TL sensitivity of MgSO4:Dy NRs is comparable with its bulk equivalent, its linear dose response extends over high doses compared with bulk MgSO4:Dy. Dose response plot of both MgSO4:Dy and MgSO4:Cu NRs have linearity up to 104Gy. The first glow peak of both NRs appears at about 400K, so these glow peaks are expected to fade rapidly at room temperature, however the higher temperature glow peaks are more stable. The fading characteristics of both NRs originate mainly from glow peaks 1 and 2. By identifying the number of component glow peaks via Tm-Tstop method and inserting them as known parameters in CGCD program, other kinetic parameters such as activation energy and order of kinetics were obtained as a result of fitting procedure. However, the kinetic parameters are trustworthy if the evaluated parameters from different methods be in accordance with each other. Variable heating rate and initial rise methods were used to obtain the activation energies. The variable heating rate method results in accurate values for the activation energy only for more intense glow peaks for them the peak temperature can easily be read for different heating rates. For satellite and overlapped glow peaks, this method encounters problem because of uncertainty in specifying the maximum peak temperature. Because of highly overlapped glow peaks, the variable heating rate method was applicable for glow peak 1of both NRs. For utilizing the initial rise method for each glow peak, the samples were first heated to the maximum temperature of the desired glow peak to remove the signals of all lower temperature glow peaks, then were cooled and were read out again to plot the initial rise part of the glow peak. The consistencies between the obtained results demonstrate the reliability of the consequences. Considering the linearity of dose response of the synthesized nano-rods up to high dose levels, they have potential application for high dose dosimetry.

References 9

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Manam, J., Das, S.,2010. Influence of Cu and Mn impurities on thermally stimulated luminescence studies of MgSO4 compound. Solid State Sciences 12, 1435-1444. McKeever, S.W.S., 1985.Thermoluminescence of Solids. Camb. University. Press. Cambridge.

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Salah,N., 2015. Thermoluminesence of gammarays irradiated CaSO4 nanorods doped with different elements.Radiat. Phys. Chem.106, 40–45. Salah, N.,Sahare, P.D., Lochabb, S.P., Kumar, P., 2006. TL and PL studies on CaSO4: Dy nanoparticles.Radiat. Meas. 41, 40-47. Singh, T.S.C.,Mazumdar, P.S., Gartia, R.K., 1988. On the determination of activation energy in thermoluminescence by the initial rise method. J. Phys. D: Appl. Phys. 21, 1312-1314. Upadhyay,A.K., Rai,R.K., Dhoble,S.J., Khokhar,M.S.K., Kher,R.S., 2011.Study of effect of mechanical deformation on thermoluminescence of gamma-ray-irradiated Dy doped MgSO4 phosphors. Radiat. Meas. 46, 1397-1401. Zahedifar, M., Sadeghi, E., Harooni, S., 2012. Thermoluminescence characteristics of the novel CaF2:Dy nanoparticles prepared by using the hydrothermal method. Nucl.Instrum. Methods B. 291, 65–72. Zahedifar, M. and Sadeghi, E., 2013.Thermoluminescence dosimetry properties of new Cu doped CaF2 nanoparticles., Radiation Protection Dosimetry,157 (3) 303-309. Zahedifar,M., Mehrabi,M.,Harooni,S.,

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Figure caption Fig 1: TL response for different impurity concentrations in (a) MgSO4:Dy, (b) MgSO4:Cu NRs. Fig 2: XRD pattern of MgSO4NRs which reveals the orthorhombic structure without additional phases. Fig 3: SEM image of the produced MgSO4NRs without using ultrasound wave(a) and with applying ultrasound (b).The NRs of Fig.3(b) were used in this study. Fig 4: EDS pattern of (a) MgSO4:Dy, (b) MgSO4:Cu NRs which confirms the formation of the desired NRs without contamination. Fig 5: Comparison of TL sensitivities ofMgSO4:M [ M=Dy,Cu= 0.1 mol% ] and pure MgSO4NRs for the administrated dose of 10 Gy.The TL glow curve of bulk MgSO4:Dy (Upadhyay et al, 2011) is also shown for comparison. Fig 6: TL dose response of (a) MgSO4:Dy, (b) MgSO4:Cu NRs . Fig 7: Fading of TL signal with the storage time for the main peak 1 (areas of peaks 1+2) and main peak 2(total area of higher temperature peaks) of: (a) MgSO4:Dy,(b)MgSO4:Cu NRs. Fig 8: Tm-Tstop plots of (a) MgSO4:Dy, (b) MgSO4:Cu NRs. Each plateau region indicates that a single glow peak exists in that region. Fig 9: Deconvoluted glow peaks of (a) MgSO4:Dy, (b) MgSO4:Cu NRs. Fig 10: plot of lnI versus

% 8

for different glow peaks of (a) MgSO4:Dy, (b) MgSO4:Cu NRs. The slop of

each straight line is –E/k.

12

Table captions Table 1: The obtained kinetics parameters of (a) MgSO4:Dy, (b) MgSO4:Cu NRs by deconvolution method.

(a)

peak

b

E (eV)

Tm (K)

Im (a.u)

1

1.02

1.25

417

48841

2

1.28

1.06

437

31276

3

1.65

0.80

491

13354

4

1. 00

1.37

552

20993

(b)

peak 1 2 3 4 5

13

b

E (eV)

Tm (K)

Im (a.u)

1.06

1.15

411

6179

1.31

1.09

434

5124

1.38

0.84

483

3517

1.10

0.92

524

1785

1.00

1.59

557

2120

Table 2: The obtained kinetics parameters of (a) MgSO4:Dy, (b) MgSO4:Cu NRs by deconvolution, variable heating rate and initial rise methods.

(a)

Peak

Eir (eV)

ECGCD (eV)

EVH (eV)

b

Tm(K)

1

1.27

1.25

1.23

1.02

417

2

1.12

1.06

------

1.28

437

3

1.09

0.80

------

1.65

491

4

1.36

1.37

------

1.00

552

(b)

peak

Eir (eV)

ECGCD(eV)

EVH (eV)

b

1

1.17

1.15

1.11

1.06

14

Tm(K)

411

2

1.11

1.09

------

1.31

434

3

0.88

0.84

------

1.38

483

4

1.01

0.92

------

1.10

524

5

1.47

1.59

------

1.00

557

Highlights · · · ·

MgSO4:Dy and MgSO4:Cu nano-rods were synthesized for the first time. Thermoluminescence dosimetry properties were studied. The nano-phosphors showed linear dose response up to very high dose levels. The synthesized nano-rods have potential application for high dose dosimetry.

15

3 4 Figure 1 5 670 (a)7 860 9 1050 11 12 1340 14 1530 16 1720 18 19 10 20 21 22 0 23 0 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

TL response (a.u)

0.5

1.5

Dy concentration (mol%)

1

2

2.5

(b)

TL response (a.u) 0

5

10

15

20

25

30

0

0.5

1.5

Cu concentration (mol%)

1

2

2.5

3 4 Figure 2 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

(a)

3 4 Figure3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

(b)

Count

(a)

3 4 Figure4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

KeV

(b)

Count

KeV

3 4 Figure5 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

TL intensity (a.u)

300

400

×7

500

700

Temperature (K)

600

× 50

The glow curve of MgSO4:Dy bulk is from [9]

0

500

1000

1500

2000

2500

800

900

MgSO4:Dy bulk

MgSO4:Cu NPS

MgSO4 NPS

MgSO4:Dy NPS

1000

3 4 Figure 6 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

3 4 Figure 7 5 6 7 8(a) 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

TL intensity (a.u)

0

10

20

0

10000

20000

30000

Storage time (day)

30

main peak2

50000

40000

main peak1

60000

70000

40

(b) TL intensity (a.u) 0

2000

4000

6000

8000

10000

0

20

Storage time (day)

10

30

main peak2

main peak1

40

3 4 Figure 8 5 (a)67 600 8 9 550 10 11 500 12 13 14 450 15 16 17 400 18 19 20 350 21 350 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

Tm (K)

400

500

Tstop (K)

450

550

600

(b)

Tm (K) 350

400

450

500

550

600

350

400

Tstop (K)

450

500

550

600

3 4 Figure 9 800 (a)56 7700 FOM= 0.97 8 9600 10 11500 12 13400 14 15300 16 17 200 18 19 20100 21 22 0 300 400 500 23 24 Temperature (K) 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

TL intensity (a.u)

600

Fitted

De-convolved

Exprimental

TL intensity (a.u) 0

10

20

30

40

50

60

70

80

90

100

300

350

400

450

Temperature (K)

FOM=0.53

500

550

Fitted

600

De-Convolved

Exprimental

3 4 Figure 10 5 6 6 (a)78 9 5 10 11 4 12 13 14 3 15 16 17 2 18 19 1 20 21 22 0 23 0.002 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

Ln I (a.u)

0.0022

1/T

0.0024

(K-1)

0.0026

0.0028

0.003

peak 4

peak 3

peak 2

peak 1

(b)

LnI (a.u) 0 0.0018

1

2

3

4

5

6

7

0.002

1/T (K-1)

0.0022

0.0024

0.0026

0.0028

0.003

peak 1 peak 2 peak 3 peak 4 peak 5