Characterizations and Nonlinear-Optical Properties of Pentanary Transition-Metal Oxysulfide Sr 2 CoGe 2 OS 6 .

As one type of material containing multiple anions, oxysulfides can combine the advantages of oxides and sulfides and are deeply studied as nonlinear-optical (NLO) materials. Herein, a new melilite-type pentanary oxysulfide Sr 2 CoGe 2 OS 6 is studied. It crystallizes in the noncentrosymmetric tetragonal space group P 4̅2 1 m , and its structure features GeOS 3 and CoS 4 tetrahedra-built {[CoGe 2 OS 6 ] 4- } ∞ layers. Its powder sample exhibits a moderate phase-matchable NLO response and a high laser-induced damage threshold. The NLO response is mainly determined by CoS 4 tetrahedra according to the theoretical calculation results. This work indicates that transition-metal oxysulfides can also be considered as potential infrared NLO materials.