Noncentrosymmetric chalcohalide K2Ba3Ge3S9Cl2: A new nonlinear optical material with remarkable laser-induced damage threshold

Chalcohalides are attractive infrared (IR) nonlinear optical (NLO) materials because they can take advantages of the large second-harmonic generation (SHG) responses of chalcogenides and high laser-induced damage thresholds (LIDTs) of halides simultaneously, which are two correlated while contradictory indicators of the NLO performance. Here, a new chalcohalide, K2Ba3Ge3S9Cl2, was synthesized by a high temperature solid-state reaction, and it crystallizes in the polar noncentrosymmetric space group P63. The fundamental structural unit [Ge3S9]6– rings formed by three corner-sharing [GeS4]4– tetrahedra construct the framework, which further connects with {[KS3Cl]6–}∞ chains to build up the structure with Ba and K/Ba cations occupying the cavities. It exhibits a widest band gap of 3.69 eV among all Ba-based chalcohalides, and a high LIDT around 28.8 times that of AgGaS2. It exhibits a SHG intensity around 0.34 times that of AGS. These experimental results are verified by theoretical calculations on its electronic structure and optical properties.