Mechanism of thermoluminescence in natural barites

The mechanism of thermoluminescence in natural barites has been investigated by comparing the TL glow curve shapes, TL emission spectra and ESR spectra of natural barites and impurity doped synthetic barium sulphate phosphors. The results of TL-ESR correlation studies indicate that the anion radicals formed on irradiation act as hole traps and are responsible for the barites TL glow curve peaks, i.e. the temperatures at which anion radicals are anihilated correspond to the temperatures of the glow peaks of natural barites. The TL mechanism involves the release of holes during the thermal activation which recombine with electrons trapped at the host cation or at lattice defect sites. Energy thus released is non-radiatively transferred to the Pb²⁺ impurity ion which is identified to be responsible for TL emission of natural barites. On return to the normal state, the Pb²⁺ ion emits its characteristic emission.