Ba 6 Zn 7 Ga 2 S 16 : A Wide Band Gap Sulfide with Phase-Matchable Infrared NLO Properties

High-performance infrared (IR) nonlinear optical (NLO) materials with large laser damage thresholds (LDTs) are urgently needed because the current commercially available AgGaS 2, AgGaSe 2, and ZnGeP 2 suffer their very low LDTs which shorten significantly their service lifetimes. Here, a novel sulfide, Ba 6 Zn 7 Ga 2 S 16 with a very wide band gap of 3.5 eV, has been discovered. This compound crystallizes in the chiral trigonal R 3 space group with a novel 3D framework that is constructed by ZnS 4 tetrahedra, Zn 3 GaS 10 supertetrahedra (a T2-type), and Zn 3 GaS 10 quadri-tetrahedral clusters via vertex-sharing. Such a novel structure exhibits desirable features which suggest a promising NLO material: phase-matchability (PM), good NLO efficiency (about half that of benchmark AgGaS 2 ), and the highest LDT among PM chalcogenides (28 times that of benchmark AgGaS 2 ). In addition, the density functional theory (DFT) calculations confirm its PM behavior and reveal that the second harmonic generation (SHG) origin is mainly ascribed to the transition process from S-3p to Ga-4p, Zn-3p, Zn-3d, and Ba-5d states; the calculated d 11 coefficient of 6.1 pm/V agrees well with experimental values.