Syntheses and characterization of three new sulfides with large band gaps: acentric Ba4Ga4SnS12, centric Ba12Sn4S23 and Ba7Sn3S13

Abstract

The desirable development of infrared nonlinear optical (IR NLO) materials is to design new compounds which exhibit wide band gaps and strong second harmonic generation (SHG) responses. Herein, we report three new sulfides, Ba₄Ga₄SnS₁₂ (1), Ba₁₂Sn₄S₂₃ (2) and Ba₇Sn₃S₁₃ (3), with wide band gaps of 2.90, 2.98 and 3.0 eV, respectively, which have been successfully synthesized for the first time. Significantly, compound 1 exhibited a large SHG coefficient (34 × KDP), illustrating a good balance between the band gap and the SHG response. Single crystal X-ray diffraction determined that compound 1 crystallizes in the non-centrosymmetric space group P2₁c and it was characterized as an interesting kite-shaped linkage motif of _∞[Ga₄SnS₁₂]. Compounds 2 and 3 crystallize in the space groups of P2₁c and Pnma, respectively. In addition, compounds 2 and 3 were characterized as zero-dimensional (0D) structures comprising isolated SnS₄ tetrahedra with Ba²⁺ cations and S²⁻ anions located between them. However, compound 2 contains extra disulfide S₂²⁻ anions in its isolated structure. Moreover, the theoretical calculations demonstrated that SHG responses for compound 1 could be ascribed to the transitions from S-3p and Ga-4p states to Ba-5d, Ga-4p and Sn-5p states. By analysing the relationship between the structures and properties for Pb₄Ga₄GeS₁₂-type compounds, it was concluded that site disorder could be an effective way to improve optical properties.