Two excellent phase-matchable infrared nonlinear optical materials based on 3D diamond-like frameworks: RbGaSnSe and RbInSnSe.

Mid- and far-infrared (MFIR) nonlinear optical (NLO) crystals with excellent performances are critical to laser frequency-conversion technology. However, the current commercial MFIR NLO crystals, including AgGaS (AGS), AgGaSe and ZnGeP, suffer from certain intrinsic drawbacks and cannot achieve a good balance between large second-harmonic generation (SHG) efficiency and high laser-induced damage thresholds (LIDTs). Herein, we report two new phase-matchable MFIR NLO chalcogenides, specifically RbXSnSe (X = Ga, In), which were successfully synthesized by high-temperature solid-state reactions. The remarkable structural feature of these materials was their 3D diamond-like framework (DLF) stacked by MSe (M = X/Sn) asymmetric building units of vertex-sharing MSe tetrahedra along the c axis. Significantly, both of the materials showed the excellent NLO performances with the desired balance between their large SHG efficiencies (4.2 and 4.8 × benchmark AGS) and large LIDTs (8.9 and 8.1 × benchmark AGS), demonstrating that the title compounds meet the crucial conditions as promising MFIR NLO candidates. Furthermore, the crystal structures, synthesis, and theoretical analysis, as well as optical properties are presented herein.