Two excellent phase-matchable infrared nonlinear optical materials based on 3D diamond-like frameworks: RbGaSn2Se6 and RbInSn2Se6

Abstract

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 AgGaS₂ (AGS), AgGaSe₂ and ZnGeP₂, 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 RbXSn₂Se₆ (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 M₃Se₉ (M = X/Sn) asymmetric building units of vertex-sharing MSe₄ 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.