Noncentrosymmetric chalcohalide NaBa4Ge3S10Cl with large band gap and IR NLO response

Abstract

By introducing a highly electronegative halide anion into chalcogenides, a novel chalcohalide, NaBa₄Ge₃S₁₀Cl, has been synthesized by a conventional high temperature solid state method. It crystallizes in a new structure type of space group P6₃, with a = 9.7653(2) Å, c = 12.0581(3) Å and Z = 2. The fundamental unit is the unique [Ge₃S₉] ring, comprised of three GeS₄ tetrahedra sharing corner S atoms. The [Ge₃S₉] rings are arranged to form pseudo layers, which are stacked through Na–Cl–Ba chains to build up the structure. The macroscopic packing of these [Ge₃S₉] rings provides the material with a moderate nonlinear optical (NLO) response at 2090 nm fundamental light. Furthermore, UV-vis-IR spectroscopy shows that NaBa₄Ge₃S₁₀Cl has a very large band gap of 3.49 eV, which is very beneficial for increasing the laser damage threshold and avoiding the two-photon absorption problem of conventional near IR laser pumping sources.