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

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 P4[combining macron]21c 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.