Li-Free ternary sulphide Cs5Ga9S16 with excellent nonlinear optical performance similar to classic LiGaS2

Abstract

The element with the strongest electropositivity, Cs, was introduced into an anionic framework [Ga₉S₁₆]⁵⁻ constructed from GaS₄ tetrahedra, which are functional nonlinear optical motifs, to acquire the ternary noncentrosymmetric sulphide Cs₅Ga₉S₁₆ through solid-state reaction in a silica tube. Similar to classic LiGaS₂, the three-dimensional phase Cs₅Ga₉S₁₆ displayed prominent nonlinear optical performance, such as second-harmonic generation intensity (equal to LiGaS₂) with phase-matching behaviour under incident laser irradiation at 1064 and 1910 nm, a wide band gap (3.81 eV) for a high laser-induced damage threshold (equal to LiGaS₂@1064 nm), and broad infrared transmittance transparency. Importantly, the Li-free Cs₅Ga₉S₁₆ avoided the problem of corrosiveness to silica tubes at high temperatures similar to LiGaS₂, suggesting that Cs₅Ga₉S₁₆ could be a promising candidate for infrared nonlinear optical applications.