Effects of different groups on phase-matching and SHG in “3+4” Pn materials

Abstract

Mid-infrared nonlinear optical (MIR-NLO) crystals are a key component in the field of high-precision measurements. Among these, phosphide (Pn; Pn = P, As) materials are renowned for their formidable polarization capabilities and hold substantial research potential. In this work, four non-cubic Pn materials (NaGe3P3, Cd3Cu2P10, Sr14Sn3As12, and Ba13Si6Sn8As22) were systematically investigated using Density Functional Theory (DFT). Notably, the four materials are all composed of tri-coordinated groups and tetra-coordinated groups (“3 + 4”). The electronic and optical properties of these materials were systematically analyzed. The strong Second Harmonic Generation (SHG) properties of Cd3Cu2P10, Sr14Sn3As12, and Ba13Si6Sn8As22 were predicted for the first time. Additionally, the contributions of different groups to polarizability and nonlinear polarizability were analyzed. In these “3 + 4” Pn materials, phase-matching was found to primarily arise from tri-coordinated groups, while the contributions to SHG predominantly stemmed from the groups with higher Pn content. The present study provides frontier theoretical guidance for high-performance MIR-NLO crystals in future research.