Abstract
The influence of rare-earth (RE) impurities as well as the host ions in the thermoluminescence (TL) of CaSO4 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 CaSO4 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 CaSO4 and follow the well known concentration quenching law; (ii) radicals like SO4-, SO3-, O3-, etc., produced by gamma irradiation, form stable trapping sites of varying activation energies which are responsible for the multipeak TL glow curves exhibited by CaSO4 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 RE3+ ions. A possible model for the process of TL in CaSO4 (RE) is also discussed.