Triplet state of F3 in LiF

Alkali halide crystals with intrinsic color centers are suitable media for solid state tunable lasers, and among them LiF is one of the most popular because of its good physical and optical qualities. The F3+ centers in this host crystal have absorption and emission properties with unusual time evolution effects after excitation. In order to clarify this particular optical cycle we investigated a γ-irradiated LiF crystal containing, besides F centers, mainly F3+ centers. The behaviour of emission and absorption as a function of temperature and pumping power confirms the existence of a triplet state.