KCd(IO ₃ ) ₂ Cl: A New UV NLO Crystal with Balanced Optical Properties Engineering via Target‐Driven Multi‐Ion Substitution Strategy

Abstract The exploration of novel nonlinear optical (NLO) materials plays a pivotal role in advancing laser science and technology. It remains a challenge to achieve a trade‐off among bandgap, second harmonic generation (SHG), and birefringence in NLO crystals. Here, pursuing these target properties, KCd(IO 3 ) 2 Cl, a novel NLO crystal, is rationally designed and synthesized through a multi‐ion substitution strategy. KCd(IO 3 ) 2 Cl crystallizes in the non‐centrosymmetric (NCS) chiral space group P 2 1 2 1 2 1 (No. 19), and it features a 3D framework composing with 2D [Cd(IO 3 )Cl] ∞ layers linked by [I(1)O 3 ] ‒ pyramids. KCd(IO 3 ) 2 Cl exhibits excellent balanced optical properties with strong SHG response (2.2 × KDP), large birefringence (0.18 @ 546 nm), wider optical transparent window (206 nm−12.0 µm), and good thermal stability (up to 392 °C). Notably, KCd(IO 3 ) 2 Cl possesses the shortest UV cutoff edge (≈206 nm) and correspondingly the broadest bandgap (6.0 eV) among the reported NCS inorganic metal iodates. As a promising UV NLO crystal, the discovery of KCd(IO 3 ) 2 Cl not only enriches the iodate halide family but also provides an effective strategy for increasing the bandgap of iodate compounds.