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

Abstract

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 AgGaS₂) are two formidable challenges in the design and development of infrared nonlinear optical (IR-NLO) candidates. In this work, a new quaternary NCS sulfide, SrCdSiS₄, has been rationally designed using the centrosymmetric SrGa₂S₄ as the template via a dual-site aliovalent substitution strategy. SrCdSiS₄ crystallizes in the orthorhombic space group Ama2 (no. 40) and features a unique two-dimensional [CdSiS₄]²⁻ layer constructed from corner- and edge-sharing [CdS₄] and [SiS₄] basic building units (BBUs). Remarkably, SrCdSiS₄ 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 × AgGaS₂). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS₄] and [SiS₄] 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.