|Year : 2011 | Volume
| Issue : 3 | Page : 185-189
Thermoluminescence and photoluminescence study of CaSO4 : Dy nanophosphor for 6 MeV energy electron dosimetry
Nandkumar T Mandlik1, Vasant N Bhoraskar1, Puroshottam D Sahare2, Bhushankumar J Patil3, Vipin Kumar2, Mukund S Kulkarni4, Sanjay D Dhole1
1 Department of Physics, University of Pune, Ganeshkhind, Pune, India
2 Department of Physics and Astrophysics, University of Delhi, Delhi, India
3 Department of Physics, University of Pune, Ganeshkhind; Abasaheb Garware Collge, Pune, India
4 RSSD, BARC, Trombay, Mumbai, India
|Date of Web Publication||27-Sep-2012|
Sanjay D Dhole
Department of Physics, University of Pune, Ganeshkhind, Pune
Source of Support: None, Conflict of Interest: None
Nanoparticles of CaSO 4 : Dy with size around 25 nm, were synthesized by the chemical co-precipitation method for the purpose of high energy electron dosimetry. The nanocrytstalline samples were irradiated with 6 MeV energy electrons having fluence varied from 3 × 10 14 to 2 × 10 15 e/cm 2 .The pre and post irradiated samples were characterized by the XRD, SEM, PL and TL techniques. The XRD spectra show the orthorhombic phase and do not change with the electron fluence. Moreover, the particle size found to be around 25 nm and marginally increased from 25 nm to 34 nm with the increase in the electron fluence. SEM image confirms the existence of the nanoparticle around 30 to 40 nm. In PL emission spectra, a shift towards lower wavelength has been observed with decrease in particle size from micrometer to nanometer. This mainly attributes to the extension in the band gap of Dy 3+ ions. The TL spectra exhibit four peaks at around 437,545,638, and 748 K respectively. The TL response curve shows that the peak intensity initially increased with electron fluence, and at a fluence of 9 × 10 14 e/cm 2 saturates then decreased with increase in the electron fluence. It is mainly due to the generation of different kinds of trapping centers. The present study indicates that the CaSO 4 : Dy phosphor can be used for the measurement of dose of 6 MeV energy electrons over a range varying from 1 kGy to 25 kGy.
Keywords: Dosimetry, electron irradiation, nanophosphor, thermoluminescence
|How to cite this article:|
Mandlik NT, Bhoraskar VN, Sahare PD, Patil BJ, Kumar V, Kulkarni MS, Dhole SD. Thermoluminescence and photoluminescence study of CaSO4 : Dy nanophosphor for 6 MeV energy electron dosimetry. Radiat Prot Environ 2011;34:185-9
|How to cite this URL:|
Mandlik NT, Bhoraskar VN, Sahare PD, Patil BJ, Kumar V, Kulkarni MS, Dhole SD. Thermoluminescence and photoluminescence study of CaSO4 : Dy nanophosphor for 6 MeV energy electron dosimetry. Radiat Prot Environ [serial online] 2011 [cited 2020 Jan 25];34:185-9. Available from: http://www.rpe.org.in/text.asp?2011/34/3/185/101716
| 1. Introduction|| |
Thermoluminescence (TL) is a well-known technique that is widely used in the dose measurement of ionizing radiations such as UV, X-rays, gamma rays and different heavy ions. The rare earth doped luminescent materials play an integral role in many applications such as drug delivery, labeling of DNA, gas sensing, etc. The phosphor CaSO 4 : Eu 2+ is used as photo luminescent liquid crystal display (PLLCD).  Nanophase materials can form new and metastable crystal structures and have potential as efficient phosphors in display applications such as new flat-panel displays with low energy excitation sources, solar-energy converters and optical amplifiers.  Nano phosphors have found their place for the measurements of high doses of ionizing radiations, where most of the microcrystalline TLD phosphors saturate. , Recently, reports give some Nano phosphors such as CaSO 4 : Dy, K 2 Ca 2 (SO 4 ) 3 : Eu, LiF: Mg,Cu,P,Ba 0.97 Ca 0.03 SO 4 : Eu and found that they are quite suitable for estimating very high doses around 100 kGy for high-energy radiations like gamma rays, protons and heavy ions. ,, In the present study CaSO 4 : Dy nano crystalline phosphor has been synthesized using chemical co-precipitation route and its photo- luminescence (PL) and thermoluminescence (TL) characteristics have been correlated with the electron dose. Better sensitivity of the nano crystalline material at high exposures can make it useful for measuring high radiation dose.
| 2. Experimental|| |
2.1 Preparation of nano phosphor
A chemical co-precipitation method was used in which nanoparticles of CaSO 4 : Dy was prepared by taking into consideration the following reaction:
A solution prepared by using 4.72 gm of calcium nitrate was dissolved in 100ml double distilled water and further 5.3 mg of DyCl 3 6H 2 O (0.1 mol%) was added in to the respective solution. Moreover, 100 ml ethanol was also added in the solution. About 2.64 gm of (NH 4 ) 2 SO 4 was dissolved in 100 ml double distilled water. (NH 4 ) 2 SO 4 solution was added to calcium nitrate solution drop wise under vigorous stirring. White precipitate was formed which was then filtered and washed several times to remove the residual salts. Nano crystalline powder samples thus obtained were dried at 413 K in an oven for 2 hours and further annealed at 973 K for 2 hours under air atmosphere in a quartz boat and quenched by taking the boat out of the furnace and placing it on a metal block for better sensitivity.
To confirm the formation of the compound and nanophase, X-ray diffraction pattern was studied at room temperature by using Cu-target (Cu-K a = 1.54°A) on Bruker AXS D8 Advance X ray Diffractometer and matched with the standard data available (JCPDS card No. 37-1496). Broadening in the X-ray diffraction lines of Nano crystalline powder sample as shown in [Figure 1] was utilized to determine the particle size by using Scherer's formula as given in Section 3.1. SEM image has been obtained by depositing the suspension in absolute ethanol (approx. 1 mg powder in 5 ml of ethanol). For taking TL, samples were exposed to electron beam from a Microtron Accelerator at various fluences from 3 × 10 14 e/cm 2 to 1.5 x 10 15 e/cm 2 . Further, TL glow curves were recorded for different electron irradiated samples on a Harshaw TLD reader (Model 3500) taking 5 mg of sample each time. They were recorded under nitrogen atmosphere at a heating rate of 5KS -1 .
2.3 Conversion factor from electron fluence to dose
The dose D in the material from the electron beam irradiation is calculated by using the formula
where the dose at the irradiated volume is expressed in Gy, the particle fluence, n is number of electron/cm 2 , r is the density of the material in g/cm 3 and (dE/dx) is the energy loss and calculated using the ESTAR code. The respective dose for different electron fluence are shown in [Table 1].
| 3. Results and Discussion|| |
3.1 XRD and particle size
[Figure 1] shows the XRD spectra for CaSO 4 : Dy Nano phosphor where the planes 111, 020, 012, 220 etc. indicate the orthorhombic phase. The average particle (grain) size of the nanoparticles was estimated from the line broadening of the prominent XRD peaks. Assuming the particles are stress free, the size can be estimated from a single diffraction peak using the Scherer's formula:
where d is the average grain size of the crystallites, λ is the incident wavelength, θ is the Bragg angle and β is the diffracted full width at half maximum (in radian) caused by the crystallites. The average grain size of the concerned phosphor is estimated to be approximately 25 nm, which confirms its Nano crystalline phase. The shape and size of these particles were also confirmed by the SEM. The SEM images shown in [Figure 2], revealed that the size of the particles varying in the range 30 to 40 nm. From XRD, the particle size found to be increased from 25 nm to 34 nm with the increase in the electron fluence. However, the difference in the estimation of the particle size is within the experimental limits and may be due to the estimation by two different methods.
|Figure 2: (a) SEM of unirradiated CaSO4: Dy Nano phosphor, (b) SEM of un-irradiated CaSO4: Dy Nano phosphor (with high resolution)|
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[Figure 3] and [Figure 4] show the PL emission and excitation spectra of the microcrystalline and Nano crystalline powder samples respectively. In case of microcrystalline sample, the emission spectra, after excitation by 350 nm consists of two bands, one at 482 nm and the other at 573 nm which are characteristics of the Dy 3+ ions due to 4F 9/2 → 6H 15/2 and 4F 9/2→6H 13/2 transitions.  In case of Nano crystalline sample, the emission spectra, after excitation by 373 nm, consists of two bands one at 424nm and the other at 510 nm which are characteristics of the Dy 3+ ions due to 4F 9/2 → 6H 15/2 and 4F 9/2→6H 13/2 transitions, respectively. The blue shift observed in the emission bands of the Nano phosphor from 573 to 510 nm and 482 to 424 nm respectively and is in agreement with the general trend on decreasing the particle size to the Nano scale. It also shows widening in the band gap of the energy levels. ,, The shift towards lower wavelength could be attributed to the expansion in the band gap of the incorporated impurities within the host of the Nano crystalline materials due to the absence of crystal field effects.  [Figure 5] shows the distinct change in the typical emission spectra for unirradiated and electron irradiated at a fluence of 1.5 × 10 15 e/cm 2 of CaSO 4 : Dy Nano phosphor. [Figure 6] shows the PL intensity as a function of electron fluence. It is observed from the [Figure 6] that the PL intensity of the electron irradiated nanomaterial is strongly dependent on the electron fluence and is found to be decreased with increase in electron fluence. This may be attributed to the electron irradiation-induced amorphization as a result of cascade quenching.  Similar results have also been observed for ion irradiation. , They revealed that this effect mainly due to the higher concentration of defects that generates nonradiative states within the forbidden gap.
|Figure 3: (a) PL Excitation spectra of Microcrystalline CaSO4: Dy at emission 573nm, (b) PL Emission spectra of Microcrystalline CaSO4: Dy excited by 350 nm|
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|Figure 4: (a) PL Excitation spectra of Nanocrystalline CaSO4: Dy at emission 510 nm, (b) PL Emission spectra of Nano crystalline CaSO4: Dy excited by 373 nm|
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|Figure 5: PL emission spectra of Nano crystalline CaSO4: Dy (a) un-irradiated sample (b) irradiated at fluence 1.5 × 1015 e/cm2|
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|Figure 6: Variation in the peak intensity of PL emission spectra with electron fluence for CaSO4: Dy Nano phosphor|
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3.3 Thermoluminescence glow curves
[Figure 7] shows typical TL glow curves for CaSO 4 : Dy Nano crystalline samples exposed to 6MeV energy electrons at various fluences from 3 × 10 14 e/cm 2 to 15 × 10 14 e/cm 2 . The glow curve of the Nano crystalline material consist of peaks at around 437, 545,638, and 748 K respectively. These peaks show the existence of the trapping centers due to electron irradiation. Moreover, there is marginal shift in the peak positions of the glow peak. This is due to the disorganization of trapping centers (TCs)/luminescent centers (LCs).
|Figure 7: TL Glow curves of CaSO4: Dy Nano phosphor for different electron fluences|
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3.4 TL response curve
The TL response curve for a peak at 545 K of these samples is shown in [Figure 8]. It is observed that the intensity of TL peak initially increases linearly with increase in electron fluence up to 9 × 10 14 e/cm 2 , then saturates till 1.2 × 10 15 e/cm 2 and further decreases with increase in the electron fluence. The fall in the TL intensity at higher fluences is because of competition between radiative and non radiative centers or sometimes between different kinds of trapping centers. ,, This competition may take place during the excitation stage or during the read-out (heating) stage.
|Figure 8: TL response of CaSO4: Dy Nano phosphor for 6MeV energy electrons|
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| 4. Conclusion|| |
The XRD and SEM results show that the CaSO 4 : Dy Nano phosphor has orthorhombic phase and the particle size increases from 25 nm to 34 nm with increase in the electron fluence. PL intensity observed to be decreased with electron fluence. Moreover, the blue shift is observed in PL when the particle size reduced from micro to nano. The intensity of TL peak initially increased with electron fluence, but after a critical fluence, decreases with further increase in the electron fluence. The results of the present study indicate that the Nano crystalline particles of CaSO 4 : Dy can be used effectively for the measurement of dose of 6 MeV electrons over a range varying from 3 ´ 10 14 e/cm 2 to 9 ´ 10 14 e/cm 2 which corresponds to 1 kGy to 25 kGy.
| 5. Acknowledgement|| |
One of the author Mr. Nandkumar Mandlik is gratefully acknowledge UGC, New Delhi for providing fellowship under Faculty Improvement Programme.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]