Thermoluminescence of CaSO4doped with rare earths

The influence of rare-earth (RE) impurities as well as the host ions in the thermoluminescence (TL) of CaSO 4 phosphors has been studied in detail by recording the TL glow curves, TL emission spectra and electron spin resonance (ESR) spectra of a number of gamma-irradiated CaSO 4 samples doped individually with different elements of the lanthanide series. It is concluded that: (i) Dy and Tm are the most efficient activators of TL in CaSO 4 and follow the well known concentration quenching law; (ii) radicals like SO 4 - , SO 3 - , O 3 - , etc., produced by gamma irradiation, form stable trapping sites of varying activation energies which are responsible for the multipeak TL glow curves exhibited by CaSO 4 phosphors; (iii) the temperatures of occurrence of the various glow peaks remain remarkably constant irrespective of the RE dopant and are directly proportional to the activation energies of the respective traps; and (iv) the TL emission spectra correspond to the fluorescence emission of RE 3+ ions. A possible model for the process of TL in CaSO 4 (RE) is also discussed.