Thermal annealing study of F center clusters in LiF single crystals

The present work is devoted to study the thermal annealing process of F center clusters (Fn) induced in LiF single crystal under high-dose γ-rays and high reactor neutrons fluence irradiations. With heating under argon atmosphere, the F-type center aggregates and gives rise to a new absorption band at 500 nm attributed to Li colloids. The optical density associated with F2 center observed in γ-ray irradiated LiF decreases with increasing annealing temperature and exhibits two distinct annealing processes with activation energies E1=0.9±0.3 eV and E2=1.6±0.5 eV. Also, it is clear from the results that the F3+ and F2 emission bands positions are affected by the irradiated dose. Reactor neutrons irradiation induces large Li colloids. These colloids persist even after annealing at 450 °C.