Designing infrared nonlinear optical crystals, Sr2MgSn2OS6 and Sr2SnGa2OS6, with hybrid anionic frameworks via a double substitution strategy†

Infrared nonlinear optical (IR NLO) crystals are crucial for advancing laser technology; however, designing and synthesizing high-performance IR NLO materials remain challenging. Heteroanionic materials effectively integrate the advantages of single-anionic counterparts, offering a promising route for synthesizing high-performance IR NLO materials. Herein, two novel heteroanionic oxychalcogenide IR NLO crystals, Sr₂MgSn₂OS₆ and Sr₂SnGa₂OS₆, are synthesized by a double substitution strategy based on the single-anionic oxide Sr₂MgSi₂O₇. They exhibit excellent optical performance, including a large phase-matched (PM) second harmonic generation (SHG) response (2 × AgGaS₂), a wide optical band gap (E_g > 3.0 eV), a large birefringence (Δn = 0.128–0.173), and a high laser-induced damage threshold (7 × AgGaS₂). The structure–performance relationship analysis indicates that these excellent performances are mainly attributed to the hybridized functional moieties. These findings strongly indicate the potential of these materials as suitable IR NLO candidates, and the strategy of double substitution proves to be effective for designing novel high-performance NLO crystals.