Crystal Growth, Structure, and Optical Properties of LiGaGe2Se6.

Large single crystals of LiGaGe2Se6 were grown, and their structure and linear optical properties were studied. According to XRD results there is some disorder because of the Li ion fluctuation and their redistribution along two cationic sites. The shape of the fundamental absorption edge versus temperature was analyzed, and direct band gap values were estimated from the Tauc plots. Raman spectra were recorded and compared with results of ab initio calculations. The high quality of LiGaGe2Se6 crystals is confirmed by signals from free and self-trapped excitons. Photoluminescence in the 696 nm broad band and a set of bands in the 950 to 1100 nm range are related to self-trapped excitons and cation antisite defects, respectively. The luminescence intensity increases two orders as the crystal is cooled to 80 K. Four peaks are observed in the thermoluminescence curves with dominant ones at 218 and 410 K. Pyroelectric luminescence in the 100 to 180 K range confirms the noncentrosymmetric structure of this crystal.