PbGa2GeS6 crystal as a novel nonlinear optical material: Band structure aspects

New quaternary sulfide PbGa2GeS6 crystal was synthesized from co-melting high-purity elements The studies of second harmonic generation and the third harmonic generation for new quaternary sulfide PbGa2GeS6 crystal have shown that its nonlinear optical response is higher with respect to other similar compounds. The band structure analysis performed by X-ray spectroscopy methods and first principles DFT band structure calculations indicate that the main contributions of the S 3p states are located at the top of valence band, while those of the Ga 4p states give contribution to the central and upper portions of the valence band of the PbGa2GeS6 compound. The calculations reveal that the band gap Eg = 2.445 eV is indirect and is formed between the valence Γ-point and the conduction X-point of Brillouin zone. The theoretically evaluated band gap energy is close to the experimental value, namely Eg = 2.37 eV at 300 K The present results allow recommending PbGa2GeS6 for nonlinear optical application in the near IR spectral range. At the same time, the crystal possesses a good transparency in the mid-IR spectral range.