Rational design via 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 ( E g > 3.5 eV) and a strong second-harmonic generation (SHG) response ( d eff > 1.0 × benchmark AgGaS 2 ) 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 4 , has been rationally designed using the centrosymmetric SrGa 2 S 4 as the template via a dual-site aliovalent substitution strategy. SrCdSiS 4 crystallizes in the orthorhombic space group Ama 2 (no. 40) and features a unique two-dimensional [CdSiS 4 ] 2- layer constructed from corner- and edge-sharing [CdS 4 ] and [SiS 4 ] basic building units (BBUs). Remarkably, SrCdSiS 4 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 E g (>3.5 eV) and a strong phase-matching d eff (>1.0 × AgGaS 2 ). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS 4 ] and [SiS 4 ] 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.