Thermoluminescence of CaSO₄ doped with rare earths

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.