Emerging pnictide materials for nonlinear optical applications: progress and challenges

Nonlinear optical (NLO) crystals are indispensable for solid-state lasers due to their unique frequency conversion capabilities, making them highly valuable for advanced photonic applications. However, developing high-performance infrared (IR) NLO crystals that meet diverse operational requirements remains a significant challenge. Pnictides have attracted growing interest in recent years because of their high NLO coefficients and great thermal conductivity. To facilitate the rational design of high-performance pnictide-based NLO crystals, this review systematically analyzes developments in the field over the past two decades. Given the compositional diversity of pnictide NLO crystals, we classify the reported compounds into four distinct systems based on their chemical constituents: [M-Pn], [A-M-Pn], [A-M-Pn-X], and [M-Pn-X] systems (where A = alkali, alkaline earth, and rare-earth metals; M = group IIIA, IVA elements, and transition metals; X = halogens; Pn = P and As). Finally, through a comprehensive analysis of pnictide NLO crystals with varying chemical compositions, we evaluate the opportunities and challenges in developing pnictides as next-generation IR NLO materials.