Optimal Design of Mid-Infrared Nonlinear-Optical Crystals: From SrZnSnSe₄ to SrZnSiSe₄

Improving the laser damage threshold (LDT) of mid-infrared nonlinear-optical (MIR NLO) crystal materials is crucial for their applications in areas such as environmental monitoring and pharmaceutical detection. This paper presents the successful synthesis of SrZnSiSe₄, a new MIR NLO crystal material that balances the LDT and second-harmonic-generation (SHG) effects and achieves phase matching. By replacement of Sn with Si in the existing SrZnSnSe₄ material, the band gap of the material was increased, resulting in an LDT that is twice that of SrZnSnSe₄, while maintaining the 2 × AgGaS₂ effect. The SHG and band gap of SrZnSiSe₄ derived from the experiments are 2 × AgGaS₂ and 1.95 eV. The band gap of SrZnSiSe₄ is better than that of SrZnSnSe₄ (1.82 eV), and the LDT of SrZnSiSe₄ is about twice that of SrZnSnSe₄. Moreover, first-nature principal calculations confirm that SrZnSiSe₄ can achieve phase matching after 1520 nm with a birefringence of 0.10, making it an excellent candidate for MIR NLO crystals.