Potassium Tetraiodatoiodate(III) Iodate(V): A Nonlinear Optical Crystal with Exceptional Second‐Harmonic Generation and Full‐Wavelength Phase Matching

The development of nonlinear optical materials with large nonlinear optical susceptibilities, wide transmission ranges, and comprehensive full-wavelength phase matching capabilities remains a significant challenge. In this study, we synthesized a novel potassium tetraiodatoiodate(III) iodate(V) via an in-situ reduction and complexation reaction. The resulting compound, K₂[I^III(I^VO₃)₄]I^VO₃, exhibits exceptional second-harmonic generation responses (21.6KH₂PO₄ at 1064 nm, 1.0KTiOPO₄ at 2050 nm), a wide transparency range from the visible to the mid-infrared wavelengths (0.37-6.05 and 7.03-13.40 µm), and a high birefringence (0.358 at 543 nm) to achieve full-wavelength phase matching. These properties are primarily ascribed to the synergistic substantial hyperpolarizability and polarizability anisotropy exhibited by the [I^III(I^VO₃)₄]^- complex ions, which comprise square-planar coordinated trivalent iodine and optimally arranged iodate ligands. This study demonstrates the pivotal role of nonmetallic cation centered coordination entities in influencing linear and nonlinear optical properties, a discovery that has significant implications for the development of innovative inorganic functional materials.