Centrosymmetric CaBaMF 8 and Noncentrosymmetric Li 2 CaMF 8 (M = Zr, Hf): Dimension Variation and Nonlinear Optical Activity Resulting from an Isovalent Cation Substitution-Oriented Design.

Zirconium/hafnium fluorides have recently been recognized as potential nonlinear optical (NLO) materials with short ultraviolet (UV) cutoff edges, which is significant in laser science and industry. The synthesis of noncentrosymmetric (NCS) materials based on centrosymmetric (CS) compounds by an isovalent cation substitution-oriented design is an emerging strategy in the NLO territory. Here, two isostructural and novel fluorides, CaBaMF 8 (M = Zr ( 1 ), Hf ( 2 )), have been synthesized through the combination of alkaline earth metals, zirconium/hafnium, and fluorine elements. They feature zero-dimensional and CS structures composed by an isolated MF 8 (M = Zr, Hf) dodecahedron and dissociative Ca 2+ and Ba 2+ cations, and they display short UV cutoff edges (<200 nm) as well. Two three-dimensional fluorides Li 2 CaMF 8 (M = Zr ( 3 ), Hf ( 4 )) are obtained by replacing Ba with alkali metal Li atom, which not only represent phase-matchable second-harmonic-generation activities (0.36, 0.30× KH 2 PO 4 (KDP)) at 1064 nm but also maintain short UV cutoff edges with high reflectance. This work has largely enriched the family of NCS zirconium/hafnium fluorides reaching the short UV region.