CaF2:MnCaF2:Mn extreme dosimeter: Effects of Mn concentration on thermoluminescence mechanisms and properties

Concentration of manganese in CaF2:MnCaF2:Mn (TLD-400) is shown to exert the most essential influence on thermoluminescent (TL) properties. The TL curve demonstrates a single high-temperature peak only when CaF2CaF2 is doped with a high manganese concentration, being close but still below the decomposition threshold of a solid solution. In case of lower manganese concentrations, the TL curve shows several peaks overlapping with each other. The optimum manganese concentration in thermoluminophor is found to be about 2.1–2.5 mol%. The influence of different factors on the actual Mn concentration in CaF2:MnCaF2:Mn is reported for the case where the material is prepared by the co-precipitation method. The CaF2CaF2 crystal lattice stress due to the Mn incorporation is studied by means of the X-ray diffraction technique. The solid solution decomposition threshold is estimated. The EPR studies of both γγ-irradiated and non-irradiated samples have demonstrated that the amount of Mn2+Mn2+ does not change as a result of the irradiation. The model of energy storage is suggested. It is based on a pair of VKVK and F centres, induced by radiation near Mn2+Mn2+, which immediately turns into an exciton-like state with a partial relaxation of the lattice stress caused by the Mn impurity. Partial relaxation of the lattice stress increases the thermal stability of the stored excitation.