K₄ZnV₅O₁₅Cl: A Congruent‐Melting Mid‐Infrared Nonlinear Optical Crystal Combined with Strong Second‐Harmonic Generation and High Laser‐Induced Damage Threshold

Abstract It is extremely challenging to accomplish second‐harmonic generation (SHG) in the whole mid‐infrared (MIR) region for oxide crystals due to their short IR absorption cutoff wavelengths. Herein, a new MIR nonlinear optical (NLO) crystal of K₄ZnV₅O₁₅Cl (KZVC) is designed and synthesized by the aliovalent substitution of [V^IIIO₅] with [Zn^IIO₄Cl] based on the K₂(VO)(V₂O₇) matrix. KZVC features an ordered 2D [ZnV₅O₁₅Cl]_∞ layered structure comprising [ZnO₄Cl] / [VO₅] square pyramids and [VO₄] tetrahedron as functional units. Importantly, KZVC shows excellently balanced performances of strong SHG responses (12 × KDP @ 1064 nm, 1.1 × AgGaS₂ @ 2.05 µm), broad IR transparency range (0.52‒10 µm), congruent‐melting behavior, and highest laser‐induced damage threshold (LIDT) (60 × AgGaS₂ @ 1064 nm) among the reported vanadates. Most remarkably, KZVC represents the first example in the oxide‐based IR NLO crystals that can achieve phase matching in a wide wavelength range extending from 1.8 to 10 µm, fully covering the important MIR atmospheric windows (3‒5 µm).