Thermoluminescence studies of CaSO₄:Dy nanophosphor for application in high dose measurements

Nanorods of CaSO₄:Dy (having diameter ∼20 nm and length ∼200 nm) were prepared by chemical coprecipitation method and their thermoluminescence (TL) characteristics were studied after annealing at different temperatures in the range 400-1000 °C. Microcrystalline material was also prepared through acid recrystallization method. TL glow curves of the nanocrystalline material annealed at 700 °C showed a major peak at around 283 °C. The effect of annealing temperature on the phase structure/morphology of particles was studied. Phase change was observed when CaSO₄:Dy was annealed at different temperatures as confirmed by XRD and TG-DTA. It was observed from the TEM images that the nanomaterial originally in the nanorods form broke into nanoparticles due to strain developed by phase change on annealing at higher temperatures. The combined effect resulted in changes in TL glow curve structure. For better clarity the TL glow curves were further deconvoluted by Computerized Glow Curve Deconvolution (CGCD) method and kinetic trapping parameters were determined. It was found that the values of kinetic parameters also changed for the nanocrystalline material annealed at different temperatures. These were also compared with the corresponding values of the microcrystalline material. It was also observed that the TL intensity saturates at about 100 Gy in case of microcrystalline phosphor, while that in case of nanocrystalline phosphor did not do saturate even up to 5 kGy.