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

Two new oxysulfides, AeGeS(2)O (Ae = Sr, Ba), were successfully synthesized via the molten salt method. The two isostructural compounds crystallize in the noncentrosymmetric space group P2(1)2(1)2(1). Their structures feature 1 infinity[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 x AgGaS2 and 0.5 x AgGaS2, respectively.