Tailored synthesis of nonlinear optical quaternary chalcohalides: Ba4Ge3S9Cl2, Ba4Si3Se9Cl2 and Ba4Ge3Se9Cl2†
Abstract
Three novel zero-dimensional quaternary chalcohalides, Ba4Ge3S9Cl2, Ba4Si3Se9Cl2 and Ba4Ge3Se9Cl2, which crystallize in the polar noncentrosymmetric space group P63 (no. 173), have been rationally synthesized by a tailored approach on the basis of unique [M3Q9]6− (M = Ge, Q = S; M = Ge/Si, Q = Se) units with Ba2+ cations and Cl− anions occupying the interspaces. The [M3Q9]6− units which consist of three Q-corner-sharing [MQ4]4− tetrahedra, are arranged along the 63 screw axis. Remarkably, Ba4Ge3S9Cl2 exhibits a strong powder second harmonic generation (SHG) response that is 2.4 times that of benchmark AgGaS2 at a laser radiation of 2.05 μm in the same particle size range of 46–74 μm. Furthermore, theoretical studies based on the density functional theory helped to gain insight into the origin of the SHG.