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.