Sn2Ga2S5: A Polar Semiconductor with Exceptional Infrared Nonlinear Optical Properties Originating from the Combined Effect of Mixed Asymmetric Building Motifs

Noncentrosymmetric (NCS) metal-chalcogenides have emerged as a candidate for infrared nonlinear optical (IR-NLO) materials, but it remains an enormous challenge to achieve simultaneously a large second-harmonic-generation (SHG) coefficient (dij), strong laser-induced damage threshold (LIDT), wide phase-matching (PM) range, and low melting point (MP) in a single material. Herein, a novel ternary mixed-metal chalcogenide, Sn2Ga2S5, was prepared via a facile mid-temperature fluxing method. It adopts a polar space group Pna21 (no. 33) and shows a distinctive 3D NCS network made by ∞2[Ga2S54–] layers and ∞1[Sn2S68–] chains via the sharing of common corners. Significantly, Sn2Ga2S5 exhibits an excellent comprehensive performance for IR-NLO applications that surpasses the current benchmark of AgGaS2, including a strong SHG response dij (2.5 × AgGaS2), high LIDT (6.6 × AgGaS2), wide PM range (>725 nm), broad transparent region (0.57–13.8 μm), and low MP (ca. 958 K). Furthermore, the detailed theoretical calculation results elucidate that the strong dij of Sn2Ga2S5 can be ascribed to the combined effect of two asymmetric building motifs (ABMs), that is, dimeric [Sn2S6] and [Ga2S5] units. Such a systematic work would provide some useful guidance for the prediction and discovery of new IR-NLO chalcogenides with mixed ABMs.