Preparation and optical properties of LiInSe2 crystals

A red LiInSe2 crystal with 20 mm in diameter and a yellow LiInSe2 crystal with 30 mm in diameter were obtained by the vertical gradient freezing method in a two-zone furnace. The thermal annealing technologies in different atmospheres were investigated. The thermal and optical properties were characterized by simultaneous differential scanning calorimetric/thermo-gravimetric (DSC-TG) analysis and an infrared (IR) spectrophotometer. Four as-grown and annealed wafers whose colors changed from red to yellow were discussed in detail on the basis of IR spectra. The results demonstrate that the transparent range of all LiInSe2 samples is from 0.6 μm to 13.5 μm. The thermal annealing processes both in vacuum and in LiInSe2 polycrystalline can obviously reduce the optical losses of red crystals. The optical losses of the deep red annealed crystal is at the level of 0.1 cm−1 in the range 2.0-8.5 μm. The yellow as-grown crystals exhibit a better transmittance especially in near IR range by comparison with red crystals.