BaGa _2GeX _6(X=S, Se): New mid-IR nonlinear optical crystals with large band gaps

摘要

New middle infrared nonlinear optical crystals of BaGa 2GeX 6(X=S, Se) have been synthesized. The structures of both BaGa _2GeS _6 and BaGa _2GeSe _6 were found to be isomorphous exhibiting a three-dimensional framework constructed by the parallel alignment of Ga or Ge tetrahedron groups along the c-aix. The ultraviolet transmittance spectrum indicates the short-wavelength absorption edges of BaGa _2GeS _6 and BaGa _2GeSe _6 are 380 nm and 440 nm, respectively. The IR transmittance spectrum shows that the absorption edge of the BaGa _2GeS _6 crystal is 13.7 μm. Second-harmonic generation of the powder samples was measured with a 2.05 μm laser using the Kurtz and Perry technique, which showed that BaGa _2GeS _6 and BaGa _2GeSe _6 are phase-matched materials, and their measured SHG coefficient is ～2.1 and ～3.5 times as large as the coefficient of AgGaS _2, or 26.3 pm/V and 43.7 pm/V.