Sn 2 Ga 2 S 5 : 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 ( d ij ), 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, Sn 2 Ga 2 S 5, was prepared via a facile mid-temperature fluxing method. It adopts a polar space group Pna 2 1 (no. 33) and shows a distinctive 3D NCS network made by ∞ 2 [Ga 2 S 5 4– ] layers and ∞ 1 [Sn 2 S 6 8– ] chains via the sharing of common corners. Significantly, Sn 2 Ga 2 S 5 exhibits an excellent comprehensive performance for IR-NLO applications that surpasses the current benchmark of AgGaS 2, including a strong SHG response d ij (2.5 × AgGaS 2 ), high LIDT (6.6 × AgGaS 2 ), 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 d ij of Sn 2 Ga 2 S 5 can be ascribed to the combined effect of two asymmetric building motifs (ABMs), that is, dimeric [Sn 2 S 6 ] and [Ga 2 S 5 ] units. Such a systematic work would provide some useful guidance for the prediction and discovery of new IR-NLO chalcogenides with mixed ABMs.