The optical properties of the nonlinear crystal BaGa4Se7

Large crystals BaGa4Se7 (BGSe), promising as a nonlinear optical converters in the mid-IR, were grown and investigated using methods of optical spectroscopy. The crystals are transparent in the range 0.465 divided by 22 mu m. The Tauc analysis showed that BGSe is a direct bandgap dielectric with E-g = 2.73 and 2.91 eV at 300 and 80 K, respectively, with dE(g)/dT = -8.07 x 10(-4) eV/K. Vibrational modes are observed in the range 150-350 cm(-1) in the Raman spectra: Thus, two-phonon absorption determines the transparency edge in the mid-IR. Main extended defects (the (001) microtwins and point defects (impurity centers such as Ga-O and different native centers) are revealed. BGSe crystals are photosensitive in the range of 1.5-4.0 eV. Luminescence in BGSe is quenched by two orders of intensity as temperature increases from 77 to 300 K. The possibility of controlling the luminescence parameters by post-growth annealing in a suitable atmosphere demonstrated. Pyroelectric luminescence in the 100-440 K range confirms the noncentrosymmetric structure of this crystal.