We report experimental study of luminescent properties of modern scintillation material SrI 2 :Eu 2+ carried out over the temperature range from 9 to 450 K by the means of the ultraviolet and vacuum ultraviolet spectroscopy with a time resolution. Photoluminescence of the Eu 2+ ions at 2.85 eV was studied under both the intracenter and interband excitations, including an X-ray excitation. The bandgap of the SrI 2 crystal has been estimated on the basis of the obtained results. In the temperature range below 100 K the intrinsic luminescence at 3.4 eV was revealed and this emission band was assigned by its properties to the luminescence of selftrapped anionic excitons in SrI 2 . The pronounced manifestation of the effect of multiplication of electronic excitations was revealed in the energy range above 2E g .

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.

AgGaSe2 and LiGaSe2 are two famous mid‐infrared nonlinear optical (NLO) materials with similar chemical formula but different structural symmetry. The former material has relatively larger NLO effect and birefringence but rather small energy band gap, while the latter is the opposite. Aiming at achieving a good balance of NLO properties, here the substitution between silver and lithium ions on the evolution of structural and optical properties in a new series of LixAg1–xGaSe2 crystals is systematically investigated. It reveals that, with the increase of Li content, LixAg1–xGaSe2 almost keeps the same tetragonal symmetry with AgGaSe2 until x ≈ 0.9. The NLO effects and birefringence values vary with respect to x with the largest variation at x = 0.8–0.9. The optimal combination of birefringence (0.03–0.025) and nonlinear parameters (26–30 pm V−1) is achieved at x = 0.4–0.5. As the energy band gap increases with the increase of x, the maximal value of 2.2 eV for chalcopyrite structure suggests that the laser‐induced damage threshold of LixAg1–xGaSe2 would be as large as five‐fold of AgGaSe2. This study provides a good example to show that the rational substitution between Li and Ag can significantly improve the balance of NLO properties in chalcogenides.

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