Effect of post-growth annealing on the optical properties of LiGaS2 nonlinear crystals

High chalcogen volatility and Li interaction with the container walls result in variation of crystal composition and presence of both extended and point defects in as-grown LiGaS2 nonlinear crystals. Annealing in appropriate conditions is used to correct the composition and improve the optical quality. We annealed LiGaS2 in vacuum, in the presence of Li2S, Ga2S3, and S, and studied changes in transmission, photoluminescence and photo-induced absorption. OH groups, S-H and S-S complexes, sulfur vacancies and cation antisite defects (GaLi) are most important. Photo-induced absorption is reversible: It appears after illumination with UV/blue light and disappears after illumination with IR light or by heating the sample.