Synthesis, crystal structures and optical properties of noncentrosymmetric oxysulfides AeGeS2O (Ae = Sr, Ba)

Abstract

Two new oxysulfides, AeGeS₂O (Ae = Sr, Ba), were successfully synthesized via the molten salt method. The two isostructural compounds crystallize in the noncentrosymmetric space group P2₁2₁2₁. Their structures feature ¹_∞[GeS₂O]²⁻ one-dimensional helical chains which are built up by [GeS₂O₂]⁴⁻ heteroanionic tetrahedra via corner sharing of O atoms. The two oxysulfides are typical semiconductors with wide bandgaps (SrGeS₂O: 3.9 eV and BaGeS₂O: 4.1 eV) that are perfectly consistent with the first-principles calculation results. They show typical band emissions under UV light excitation (SrGeS₂O: 375 nm and BaGeS₂O: 360 nm). In addition, SrGeS₂O also possesses an orange-yellow light emission (572 nm). SrGeS2O and BaGeS2O exhibit moderate second harmonic generation (SHG) intensities of 0.4 × AgGaS₂ and 0.5 × AgGaS₂, respectively.