Recent progress in iodate based nonlinear optical crystals.

Nonlinear optical (NLO) crystals are essential components in modern laser technology. For middle and far-infrared applications, iodates are regarded as highly promising materials due to their intrinsic non-centrosymmetric (NCS) structures, broad optical transparency, pronounced second-order NLO responses, and relatively high laser-induced damage thresholds (LIDTs). However, the tendency of spontaneous crystallization in favor of thermodynamically stable centrosymmetric (CS) phases poses a significant challenge to the rational design of iodates with a macroscopic NCS framework. This review systematically summarizes recent advances over the past decade in the rational designs and controlled syntheses of NCS iodates with significant SHG responses. Emphasis is focused on five key structural-modulation strategies: polymerization of different iodate anions, aliovalent substitution, fluorine substitution, and the synergistic integration of iodate anions with either planar π-conjugated units or tetrahedral building blocks. These approaches collectively enhance local polarization, tune the electronic structure, and optimize crystal-growth kinetics, thereby increasing the probability of forming NCS structures and promoting the development of high-performance iodate NLO crystals. Finally, future research directions and emerging trends in this field are outlined to provide a reference for the continued advancement of related research areas.