A review of thermoluminescence of calcium fluoride, calcium sulphate and calcium carbonate

CaF2, CaSO4 and CaCO3 are available in mineral form as fluorite, anhydrite and calcite respectively. Fluorite and calcite emit intense thermoluminescence (TL). Most intense glow peaks in the temperature region 200-250degC, are exploited in thermoluminescent dosimetry (TLD). Rare earth (RE) and manganese impurity ions form efficient TL emission centres. The TL emission mechanism involves the reduction of RE3+ ions during irradiation and their re-oxidation during heating and emission of TL light. In Mn2+ doped phosphors, the energy released during recombination gets non-radiatively transferred from the recombination centre to the Mn2+ ion located in the close vicinity. The association of Ce3+ (recombination centre) with interstitial F- or substitutional O2- (hole traps) is reflected in the spectra of CaF2 glow peaks. The models of TL mechanism related to different types of centres are illustrated. The phosphors are left with a considerable number of unannealed traps even after the TL has been read up to 350degC. These residual traps produce photo-transferred thermoluminescence (PTTL) which is useful for studying glow peak kinetics. (author)