LiAgCe₂F₁₀(H₂O)₂: Focusing on the Cation Size Effect to Reasonably Design a Nonlinear Optical Hydrated Cerium(IV) Fluoride

Rare-earth-based materials are pivotal in optical applications, particularly as nonlinear optical (NLO) materials, owing to their exceptional structural tunability and functional properties. In this study, a novel fluoride, AgCe₃F₁₃, was synthesized via a facile hydrothermal method combined with a cation substitution strategy, wherein Ag⁺ ions replaced NH₄⁺ ions in the parent compound NH₄Ce₃F₁₃. To further tailor the crystal structure, Li⁺ ions were introduced, yielding a new noncentrosymmetric hydrated fluoride, LiAgCe₂F₁₀(H₂O)₂. Structural analysis reveals that AgCe₃F₁₃ comprises interconnected [Ce₃F₂₂]^10- clusters and [Ag₂F₉]^7- dimers, while LiAgCe₂F₁₀(H₂O)₂ features unique {[LiAgF₅(H₂O)₂]^3-}_∞ chains and {[Ce₂F₁₀]^2-}_∞ pseudolayered motifs. Notably, LiAgCe₂F₁₀(H₂O)₂ exhibits a phase-matchable second-harmonic generation (SHG) response with an efficiency of approximately 0.6 times that of KH₂PO₄ (KDP). This work demonstrates the efficacy of cation modulation as a versatile strategy for the design of advanced functional optical materials.