From CaBaM 2 F 12 to K 2 BaM 2 F 12 (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, d 0 transition metals, and F atom has generated two new and isostructural fluorides, CaBaZr 2 F 12 (CBZF) and CaBaHf 2 F 12 (CBHF), which adopt centrosymmetric space group I 4/ mmm . Taking CBZF and CBHF as the parents, two new fluorides, K 2 BaZr 2 F 12 (KBZF) and K 2 BaHf 2 F 12 (KBHF), with an Imm 2 polar structure were obtained via a heterovalent cation substitution strategy. All four compounds feature ZrF 8 -dodecahedra-built {[Zr 2 F 12 ] 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 × KH 2 PO 4 (KDP)] under 1064 nm laser radiation. This work enriches fluorides as promising short-wavelength NLO materials.