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...

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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 SrZnSiSe 4 , 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 SrZnSnSe 4 material, the band gap of the material was increased, resulting in an LDT that is twice that of SrZnSnSe 4 , while maintaining the 2 × AgGaS 2 effect. The SHG and band gap of SrZnSiSe 4 derived from the experiments are 2 × AgGaS 2 and 1.95 eV. The band gap of SrZnSiSe 4 is better than that of SrZnSnSe 4 (1.82 eV), and the LDT of SrZnSiSe 4 is about twice that of SrZnSnSe 4 . Moreover, first-nature principal calculations confirm that SrZnSiSe 4 can achieve phase matching after 1520 nm with a birefringence of 0.10, making it an excellent candidate for MIR NLO crystals.

The symmetry of crystals is an extremely important property of crystals. Crystals can be divided into centrosymmetric and non-centrosymmetric crystals. In this paper, an infrared (IR) nonlinear optical (NLO) material AgGaGeSe4 was synthesized. The related performance analysis, nonlinear optical properties, and first-principle calculation of AgGaGeSe4 were also introduced in detail. In the AgGaGeSe4 structure, Ge4+ was replaced with Ga3+ and produced the same number of vacancies at the Ag+ position. The low content of Ge doping kept the original chalcopyrite structure and improved its optical properties such as the band gap. The UV-Vis diffuse reflection spectrum shows that the experimental energy band gap of AgGaGeSe4 is 2.27 eV, which is 0.48 eV larger than that of AgGaSe2 (1.79 eV). From the perspective of charge-transfer engineering strategy, the introduction of Group IV Ge elements into the crystal structure of AgGaSe2 effectively improves its band gap. The second harmonic generation (SHG) effect of AgGaGeSe4 is similar to that of AgGaSe2, and at 1064 nm wavelength, the birefringence of AgGaGeSe4 is 0.03, which is greater than that of AgGaSe2 (∆n = 0.02). The results show that AgGaGeSe4 possessed better optical properties than AgGaSe2, and can been broadly applied as a good infrared NLO material.