RESUMO
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.
RESUMO
Increasing the energy band gap under the premise to maintain a large nonlinear optical (NLO) response is a challenging issue for the exploration and molecular design of mid-infrared nonlinear optical crystals. Utilizing a charge-transfer engineering method, we designed and synthesized a rare earth chalcogenide, KYGeS4. With an NLO effect as large as that in AgGaS2, KYGeS4 breaks through the limitation of energy band gap, i.e., the "3.0 eV wall", in NLO rare earth chalcogenides, and thus exhibits an excellent comprehensive NLO performance. First-principles electronic structure analysis demonstrates that the large band gap in KYGeS4 is ascribed to the decreased covalency of Y-S bonds by transferring charge from [YS7] to [GeS4] polyhedra. The charge-transfer engineering strategy would have significant implications for the exploration of good-performance NLO crystals.
