Infrared nonlinear optical sulfide CsCd4In5S12 exhibiting large second harmonic generation response

A new infrared nonlinear optical quaternary sulfide, CsCd4In5S12, was successfully synthesized via a high-temperature reaction using the CsI flux. This new compound adopts the KCd4Ga5S12-type structure crystallizing in the non-centrosymmetric (NCS) space group R3 (No. 146). It features a 3D diamond-like network constructed by vertex-sharing distorted [CdS4]6− and [InS4]5− tetrahedra which are aligned along the c axis with Cs+ cations dispersing in the cavities. It possesses a direct optical band gap of 2.47 eV with a wide transparency range (0.53–25 μm) and high thermal stability up to 1061 K. Moreover, CsCd4In5S12 achieves a good balance between a high laser-induced damage threshold (LIDT, 9.3 × AgGaS2 in the size range of 150–200 μm) and strong powder second-harmonic generation (SHG, 1.1 × AgGaS2) with phase matching (PM) behavior. Theoretical calculations revealed that the band edges are mainly composed of In–S bond orbitals, which make the dominant contribution to the NLO response.