Rational Design and Synthesis of a Deep-Ultraviolet Nonlinear Optical Fluorinated Orthophosphate: BaZn(PO₄)F

Rational design and tailored synthesis of noncentrosymmetric compounds with nonlinear optical (NLO) properties, especially in the deep-ultraviolet (deep-UV) region, remains a great challenge. Herein, we report on the development of a modified fluoro-solvo-hydrothermal method with two additive reagents (trimethylamine and NaF solution) as the solvents, using BaFe(PO₄)(OH) ( P2₁2₁2₁) as the prototype, for the rational design and tailored synthesis of the first deep-UV fluorinated orthophosphate, BaZn(PO₄)F. It crystallizes in the polar space group Pna2₁ and exhibits transparency down to deep-UV region (<190 nm) with SHG effect at 0.26 × KH₂(PO₄). Its structure is built from strictly alternating ZnO₄F trigonal bipyramids and PO₄ tetrahedra, resulting in a four-connected ABW-type zeolite framework. First-principles calculations confirm the deep-UV absorption edge and reveal that ZnO₄F plays an essential role in the NLO properties. The synergetic effect of Zn and F atoms leads to its more polar crystal structure, much deeper absorption edge, and better SHG effect than the prototype.