La2ZnGa2S6O: A Melilite-Type Transition Metal Oxysulfide achieving a Well-Balanced Nonlinear-Optical Behavior

Abstract

Combination of multiple anions (S2- and O2-) was developed as an effective method for exploring new excellent nonlinear optical (NLO) oxysulfides with adjustable property based on the flexible anion (S/O) ratio in structures. Note that mixed melilite-type oxysulfides with mixed alkaline-earth (Ae) and trivalent lanthanide (Ln) metals exhibit the natural noncentrosymmetric (NCS) and disordered structures that show the good NLO property. Herein, we introduced the low-coordination ZnS4 to replace with high-coordination AeS8 into La-based melilite to break the initial disordered structure for the born of a La2ZnGa2S6O NLO material with ordered-structure. Property investigation shows that La2ZnGa2S6O achieves a well-balanced NLO behavior between wide optical bandgap (3.0 eV) and ultra-strong phase-matching second harmonic generation (SHG) response (1.9 × AgGaS2). Among the melilite-type transition-metal oxysulfides, La2ZnGa2S6O exhibits the largest powder SHG response that can be attributed as the synergetic contributions of LaS7O, ZnS4 and GaS3O anionic groups based on the SHG-density analysis, which indicates that La2ZnGa2S6O is a potential NLO candidate for frequency-conversion application and combination of transition- and lanthanide-metals into structure provides a feasible way to design new large SHG oxysulfides.