Cd₄SiQ₆ (Q = S, Se): Ternary Infrared Nonlinear Optical Materials with Mixed Functional Building Motifs

Two ternary infrared nonlinear optical materials Cd₄SiS₆ (1) and Cd₄SiSe₆ (2) with polar space group Cc were obtained by mixing d¹⁰ configurations-central tetrahedra motifs and nonlinear optical (NLO)-active distorted M^IVQ₄ tetrahedra motifs in a non-alkaline earth metals-containing system. They exhibited an interesting three-dimensional (3D) framework structure, and millimeter-level single crystals were successfully grown by a chemical transport reaction. Comprehensive optical measurements indicated that they achieve coexistence of good second-harmonic generation (SHG) responses (1.3 and 1.9 × AgGaS₂ at 74–106 μm particle size) and high laser-induced damage thresholds (8.6 and 7.1 × AgGaS₂ at 1064 nm laser) and wide infrared (IR) transparent regions (0.45–17.6 μm for 1, 0.64–20.3 μm for 2). Furthermore, theoretical studies revealed that their SHG effects originate from two functional building motifs (FBMs) CdQ₄ and SiQ₄ tetrahedra, shedding light on the exploration of new IR NLO materials with mixed FBMs.