Rational design dual-site aliovalent substitution leads to an outstanding IR nonlinear optical material with well-balanced comprehensive properties.

The acquisition of a non-centrosymmetric (NCS) structure and achieving a nice trade-off between a large energy gap ( > 3.5 eV) and a strong second-harmonic generation (SHG) response ( > 1.0 × benchmark AgGaS) are two formidable challenges in the design and development of infrared nonlinear optical (IR-NLO) candidates. In this work, a new quaternary NCS sulfide, SrCdSiS, has been rationally designed using the centrosymmetric SrGaS as the template a dual-site aliovalent substitution strategy. SrCdSiS crystallizes in the orthorhombic space group 2 (no. 40) and features a unique two-dimensional [CdSiS] layer constructed from corner- and edge-sharing [CdS] and [SiS] basic building units (BBUs). Remarkably, SrCdSiS displays superior IR-NLO comprehensive performances, and this is the first report on an alkaline-earth metal-based IR-NLO material that breaks through the incompatibility between a large (>3.5 eV) and a strong phase-matching (>1.0 × AgGaS). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS] and [SiS] BBUs is the main origin of the strong SHG effect and large birefringence. This work not only provides a high-performance IR-NLO candidate, but also offers a feasible chemical design strategy for constructing NCS structures.