A highly efficient thermoluminescence Na2SO4 phosphor with thenardite polymorphic structure was prepared by simple slow evaporation technique followed by subsequent calcination at 200°C, 400°C, and 600°C for 4？h and the resultant crystals were characterized by various analytical techniques. All the samples exhibited thermodynamically stable thenardite phase and the grain growth was increased for the calcined samples. SEM analysis indicated the fine distribution of twinned orthogonal prism and pyramidal structure without any agglomeration. The electron spin resonance spectroscopy showed the existence of radicals as trap centre. The thermoluminescence behavior suggested the charge carrier recombination dynamics in the thenardite sample followed second-order kinetics. The trapping parameters such as activation energy ( ), order of kinetics ( ), and frequency factor ( ) have been determined using Chen’s peak shape method. Further fading of the TL intensity of Na2SO4 showed that thenardite is quite suitable for radiation dosimetry even up to 15 days. The photoluminescence band of Na2SO4 reduced in its intensity after γ-irradiation, suggesting that defects are unstable and decay rapidly. 1. Introduction Sulphates are attractive candidates in thermoluminescence (TL) dosimetry for the quantitative measurement of radiation dose. Due to high cost of the most popular TL dosimeters and also due to some competitions attending its reuse such as permanent radiation damage effects and the sensitivity to the annealing temperature much attention focused towards the innovation of new phosphor materials. Sodium sulphate (thenardite), though very simple in chemical composition, has been the subject of various applications. It is used for the production of glasses and paints and for thermal energy storage techniques [1, 2]. Na2SO4 exhibits a variety of phase transitions between its five anhydrous polymorphs (labelled I–V). The phase transformation sequence among the Na2SO4 polymorphs can be described as Na2SO4 forms two naturally occurring minerals mirabilite (Na2SO4？:？10H2O) and thenardite (Na2SO4). Both are in thermodynamic equilibrium at 32°C which may be lowered to 18°C in the presence of foreign ions [3]. At room temperature phase V (thenardite) is reported to be stable while phase III is metastable. Phase I, and II are high-temperature polymorphs however, phase II is reported to have a narrow stability zone. Phase IV is considered to be metastable and its phase relation and structure have yet to be well established [4–7]. Correcher et al. observed the spectra of
References
[1]
J. P. Elder, “Thermal energy storage materials-a DSC study,” Thermochimica Acta, vol. 36, no. 1, pp. 67–77, 1980.
[2]
H. G. Wiedemann, “Thermal studies on thenardite,” Thermochimica Acta, vol. 50, no. 1–3, pp. 17–29, 1981.
[3]
O. Braitsh, Entstehung, and K. S. D. Salzlagerstallen, Springer, New York, NY, USA, 1962.
[4]
S. Gomathy, P. Gopalan, and A. R. Kulakarni, “Effect of Homovalent anion doping on the conductivity and phase transitions in Na2SO4,” Journal of Solid State Chemistry, vol. 146, no. 1, pp. 6–12, 1999.
[5]
F. C. Kracek and R. E. Gibson, “The polymorphism of sodium sulfate: III. Dilatometer investigations,” Journal of Physical Chemistry, vol. 34, no. 1, pp. 188–206, 1930.
[6]
B. K. Choi, H. K. Lee, and Y. W. Kee, “Ionic conduction and structural phase transitions of Na2SO4 doped with various impurities,” Solid State Ionics, vol. 113–115, pp. 493–499, 1998.
[7]
C. R. Navarro, E. Doehne, and E. Sebastian, “How does sodium sulfate crystallize? Implications for the decay and testing of building materials,” Cement and Concrete Research, vol. 30, no. 10, pp. 1527–1534, 2000.
[8]
V. Correcher, J. Garcia-Guinea, P. Lopez-Arce, and J. M. Gomez-Ros, “Luminescence emission spectra in the temperature range of the structural phase transitions of Na2SO4,” Spectrochimica Acta A, vol. 60, no. 7, pp. 1431–1438, 2004.
[9]
A. Sidike, K. Niyazi, H. Zhu, K. Atobe, and N. Yamashita, “Photoluminescence properties of thenardite from Ai-Ding Salt Lake, Xinjiang, China,” Physics and Chemistry of Minerals, vol. 36, no. 3, pp. 119–126, 2009.
[10]
H. C. Freiheit, “Order parameter behaviour and thermal hysteresis at the phase transition in the superionic conductor lithium sodium sulfate LiNaSO4,” Solid State Communications, vol. 119, no. 8-9, pp. 539–544, 2000.
[11]
A. Choubey, S. K. Sharma, S. P. Lochab, and D. Kanjilal, “Effect of ion irradiation on the thermoluminescence properties of K2Ca2(SO4)3 phosphor,” Radiation Effects and Defects in Solids, vol. 166, no. 7, pp. 487–500, 2011.
[12]
A. G. Nord, “Refinement of the crystal structure of thenardite, Na2SO4(V),” Acta Chemica Scandinavica, vol. 27, pp. 814–822, 1973.
[13]
F. C. Hawthorne and R. B. Ferguson, “Anhydrous sulphates. I: refinement of the crystal structure of celestite with an appendix on the structure of thenardite,” The Canadian Mineralogist, vol. 13, pp. 181–187, 1975.
[14]
W. Eysel, “Christal chemistry of the system Na2SO4-K2SO4-K2CrO4-Na2CrO4 and the glaserite phase,” American Mineralogist, vol. 58, pp. 736–747, 1973.
[15]
K. Tanaka, H. Naruse, H. Morikawa, and F. Marumo, “Phase-transition process of Na2SO4(III) to Na2SO4(I) and anharmonic thermal vibration,” Acta Crystallographica B, vol. 47, pp. 581–588, 1991.
[16]
O. Braitsh, Entstehung, and K. S. D. Salzlagerstallen, Theory of Magnetic Resonance, Springer, New York, NY, USA, 2nd edition, 1962.
[17]
R. Huzimura and K. Atarachi, “The role of sulphur-oxy radicals in thermoluminescence and exoelectron emission of CaSO4, phosphors,” Physica Status Solidi (A), vol. 70, no. 2, pp. 649–657, 1982.
[18]
C. L. P. Mauricio, E. Bortolin, and S. Onori, “ESR study of CaSO4:Dy TLD,” Radiation Measurements, vol. 26, no. 4, pp. 639–644, 1996.
[19]
T. K. Gundu Rao, B. C. Bhatt, J. K. Srivastava, and K. S. V. Nambi, “On the sulphoxy radicals in CaSO4:Dy,Na thermoluminescent phosphor: electron paramagnetic resonance studies,” Journal of Physics, vol. 5, no. 12, pp. 1791–1800, 1993.
[20]
V. Natarajan, T. K. Seshagiri, R. M. Kadam, and M. D. Shastri, “SO4--SO3- radical pair formation in Ce doped and Ce, U co-doped K3Na(SO4)2: EPR evidence and its role in TSL,” Radiation Measurements, vol. 35, no. 4, pp. 361–368, 2002.
[21]
T. Hayakawa and M. Ohta, “Role of dopant on the formation of SO3- radical induced by X-ray irradiation in K3Na(SO4)2 crystals,” Journal of Luminescence, vol. 81, no. 4, pp. 313–319, 1999.
[22]
K. S. V. Nambi, V. N. Bapat, and A. K. Ganguly, “Thermoluminescence of CaSO4 doped with rare earths,” Journal of Physics C, vol. 7, no. 23, Article ID 4403, 1974.
[23]
M. Magharbi and D. E. Arafah, “Sensitization of the thermoluminescence response of CaF2 phosphors,” Physica Status Solidi (A), vol. 195, no. 2, pp. 459–467, 2003.
[24]
R. Chen and Y. Kirish, Analysis of Thermally Stimulated Processes, Pergamon, New York, NY, USA, 1981.
[25]
I. Y. Kushnirenko, S. G. Nedelko, and N. P. Smoyar, “Spectral behavior of electron-oscillations in luminescence centres of alkali metals activated by molecular anions S2-,” Ukrainakii Flzicheakil Zhurnal, vol. 35, p. 855, 1990.
[26]
D. N. Govorun, I. Y. Kushunirenko, S. G. Nedel’ko, V. P. Sakun, and N. P. Smoyar, “Luminescent properties of S2- impurity molecular anions in Rb2SO4 crystals,” Zhurnal Prikladnoi Spektroskopii, p. 930, 1990.
[27]
S. G. Nedel’ko, M. M. Podshivailov, N. P. Smoyar, and V. I. Shelud’ko, “Vibronic interactions in luminescent impurity centers “molecular anion-defect” in ionic and heterodesmic crystals,” Zhurnal Prikladnoi Spektroskopii, vol. 55, p. 836, 1991.
[28]
M. U. Belyi, S. G. Nedel’ko, and V. I. Shelud’ko, “Luminescence of alkali metal sulfate crystals with sulfur impurity,” Zhurnal Prikladnoi Spektroskopii, vol. 61, p. 283, 1994.
