From CaBaM2F12to K2BaM2F12(M = Zr, Hf): Heterovalent Cation-Substitution-Induced Symmetry Break and Nonlinear-Optical Activity

Designing short-wavelength nonlinear-optical (NLO) crystals is of vital importance for laser applications. Here, the combination of alkaline-earth metals, d0transition metals, and F atom has generated two new and isostructural fluorides, CaBaZr2F12(CBZF) and CaBaHf2F12(CBHF), which adopt centrosymmetric space group I4/mmm. Taking CBZF and CBHF as the parents, two new fluorides, K2BaZr2F12(KBZF) and K2BaHf2F12(KBHF), with an Imm2 polar structure were obtained via a heterovalent cation substitution strategy. All four compounds feature ZrF8-dodecahedra-built {[Zr2F12]4–}∞chains and show short ultraviolet cutoff edges (<200 nm). KBZF and KBHF show phase-matchable behavior with moderate second-harmonic-generation responses [0.6 and 0.35 × KH2PO4(KDP)] under 1064 nm laser radiation. This work enriches fluorides as promising short-wavelength NLO materials.