Structure and optical properties of Li2Ga2GeS6 nonlinear crystal

•The Li2Ga2GeS6 single crystals of optical quality were grown by the Bridgman technique.•Crystal structure is determined (Fdd2). Well-resolved Raman spectrum was obtained.•Fundamental absorption edge is analyzed and band gap estimated. S–S vibrations are indicated.•Emissions of free and self-trapped excitons confirm high crystal quality.•Crystals demonstrate an intense photoluminescence which increases two orders at cooling.

Structure and optical properties of new nonlinear crystal – Li2Ga2GeS6 single crystal of optical quality, grown by the Bridgman technique were studied. The data on transmission, Raman scattering, luminescence emission, excitation and thermal quenching as well as thermostimulated luminescence are presented. Fundamental absorption edge is determined by the direct allowed electronic transitions: The values of optical band gap are estimated. Absorption band at 8.0 μm is due to S–S vibrations. Features in photoluminescence spectra are associated with excitons: both free (narrow line at 371 nm) and self-trapped ones (broad bands at 596, 730 and 906 nm). Spontaneous emission in the 80–170 K range, both at crystal heating and cooling, is typical of pyroelectrics: This confirms the absence of symmetry center in Li2Ga2GeS6 and an opportunity of laser frequency nonlinear conversion.