CaF2, CaSO4 and CaCO3 are available in mineral form as fluorite, anhydrite (or gypsum) and calcite (or aragonite) respectively. Fluorite and calcite emit intense thermoluminescence (TL). All three materials can be prepared in the laboratory as highly sensitive TL phosphors by crystal growth or sintering techniques. TL glow peaks appear in a wide temperature range from liquid nitrogen temperature (LNT) up to 650 oC. Most intense glow peaks, which appear in the temperature region of 200-250 oC, are usefully exploited in thermoluminescence dosimetry (TLD). Rare earth (RE) and manganese impurity ions form efficient TL emission centres in the mineral as well as the synthetic varieties of these materials. The TL emission mechanism involves the reduction of RE3+ doped phosphors, the energy released during recombination gets non-radiatively transferred from the recombination centre to the Mn2+ ion located in the close vicinity. This leads to excitation of Mn2+ ion resulting in its characteristic emission. While in most of the cases traps and recombination centres seem to be randomly distributed with respect to each other, there are some centres in which these are spatially associated. The association of Ce3+ (recombination centre) with interstitial F- or substitutional O2- (hole traps) is clearly reflected in the spectra of individual glow peaks of CaF2. 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 350 oC. These unannealed high temperature residual traps are used to produce photo-transferred thermoluminscence (PTTL). Apart from being useful in re-estimation of dose and in UV measurements, the phenomenon of PTTL provides a useful means of studying the kinetics of the glow peaks.
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C.M. Sunta (1984) studied this question.