Optimizing the Hydrogen-Bond Network Drives Cadmium Ce(IV) Fluoride Hydrate with Significantly Enhanced Optical Anisotropy.

The controlled engineering of ordered crystal structures has emerged as a powerful strategy for the development of functional materials with enhanced optical properties. Herein, three novel cadmium Ce(IV) fluoride hydrates─CdCeF(HO), CdCeF(HO), and CdCeF(HO)─have been obtained by simple hydrothermal methods. Birefringence calculations reveal a progressive increase in Δ values: 0.009@546 nm for CdCeF(HO), 0.042@546 nm for CdCeF(HO), and 0.147@546 nm for CdCeF(HO). The measured birefringence of CdCeF(HO) reaches 0.152@546 nm, surpassing most known rare-earth fluorides. Combined structural and theoretical investigations demonstrate that the observed enhancement originates from the concerted alignment of anisotropic [(CeF)] chains and {[Cd(HO)]} chains mediated by hydrogen-bonding networks, synergistically coupled with ordered interlayer stacking configurations. This work enriches the diversity of rare-earth fluorides, promoting further research into the development of promising rare-earth fluoride birefringent materials.