Thermoluminescence, ESR and x-ray diffraction studies of CaSO4 : Dy phosphor subjected to post preparation high temperature thermal treatment

Thermoluminescence (TL), electron spin resonance (ESR) and x ray diffraction studies of CaSO(4) : Dy phosphor subjected to post preparation high temperature treatment were carried out. Analysis of the TL glow curve indicated that the dosimetric glow peak at 240 degrees C reduces, whereas the low temperature satellite peak increases with the increase in the annealing temperature in the range 650-1000 degrees C. The influence of the annealing atmosphere on the TL glow curve structure was also observed. Reduction of the photoluminescence intensity of the annealed phosphor indicated that the environment of Dy(3+) ions might have undergone some change due to high temperature treatment. Reduction in the ESR signal intensity corresponding to O(3)(-) and SO(3)(-) radicals was observed initially with the increase in the annealing temperaure; subsequently their intensity increased with temperature. Signals due to the SO(4)(-) radical vanished, when the phosphor was annealed beyond 800 degrees C. A signal corresponding to SH(2)(-) radicals was also observed in the ESR spectra for samples subjected to annealing in the temperature regime 800-1000 degrees C. XRD of the in situ annealed phosphor showed a change in the unit cell parameters. An endothermic peak at 860 degrees C in the DTA spectrum was observed.