Syntheses, Structures, and Nonlinear Optical Properties of Two Sulfides Na2in2ms6 (M = Si, Ge)

The first two new Na-containing sulfides Na₂In₂MS₆ (M = Si (1), Ge (2)) in the Na₂Q-B₂Q₃-CQ₂ (B = Ga, In; C = Si, Ge, Sn; Q = S, Se) system were prepared for the first time through conventional high-temperature solid-state reaction. They are isostructural with space group Cc (No. 9) in monoclinic phases and feature three-dimensional frameworks built by the (∞)¹[In₂MS₆]²⁻ (M = Si, Ge) chains through corner-sharing InS₄ tetrahedra and MS₄ (M = Si, Ge) tetrahedra, with Na⁺ cation located in the cavities. They display moderate second harmonic generation (SHG) conversion efficiencies compared with commercial AgGaS₂, with phase-matching behavior at 1800 nm and laser-induced damage thresholds 6.9 and 4.0 times higher than that of AgGaS₂, respectively. Therefore, the output SHG intensities of 1 and 2 will be ∼4.3 and 4.0 times larger than that of AgGaS₂, when the intensity of incident laser increased to close the damage energy of 1 and 2, indicating their potential for high-power nonlinear optical application.