Thermoluminescence in pure LiF crystals: Glow peaks and their connection with color centers.

Nominally pure LiF crystals were irradiated with the same dose (0.85 106 R) of gamma rays at ambient and low temperatures (-60 °C) and the resulting thermoluminescence (TL) is reported. Various optical and thermal treatments were applied in order to change the concentration of color centers (CCs). The effect of such treatments on the glow curves is observed. Knowing the coloration from optical transmission and photoluminescence measurements made on the same samples, we attribute many of the glow peaks (GPs) to the annealing of F center aggregates. For the present conditions of irradiation and dose, TL processes begin with decay of F3+ centers that display a GP at 164 °C. F3(R) centers follow and are responsible for GPs at 193 and 228 °C. A GP at 263 °C is ascribed to F2 centers. Several peaks at temperatures in the range of 280–380 °C are associated with impurity perturbed F centers. A GP at 410 °C is associated with a complex of aggregated F and H centers. These attributions are accomplished by means of TL spectra, optical transmission spectra, and annealing procedures, and are critically discussed. The experimental data confirm the general trend of thermal stability of CCs, which decreases by moving from simple F centers to more complex ones, and the existence of exchange dynamics among CCs. [ABSTRACT FROM AUTHOR]