Identification of multiple charge carrier trapping centers in irradiated LiF:Mg,Ti via optical absorption studies: The 2.78 eV and 5.0 eV (F center) absorption bands

The optical absorption (OA) and thermoluminescence (TL) of irradiated LiF:Mg,Ti (TLD-100) was studied as a function of the temperature of post-irradiation annealing using the I_m-T_stop and T_m-T_stop techniques. Computerised deconvolution was used to resolve the OA spectra into individual Gaussian bands and the TL glow curve into component glow peaks. Preferential population of the 2.78 eV OA band at high ionisation density suggests that this band may arise from a multiple ("two-hit") charge carrier trapping structure. The remarkable similarity between the thermal bleaching behaviour of the "single-hit" 5.0 eV (F -band) and the 2.78 eV band leads to the suggestion that the 2.78 cV band arises from an F₂ trapping center, i.c., two adjacent anion vacancies which together capture two electrons.