Exploring a new short-wavelength nonlinear optical fluoride material featuring unprecedented polar cis-[Zr6F34]10− clusters

Abstract

Traditional fluorides are rarely reported as candidates for nonlinear optical (NLO) materials featuring a deep-ultraviolet cutoff edge. Theoretical investigations suggest that the ZrF₈ dodecahedron shows large polarizability anisotropy and benefits for large birefringence. Herein, a new fluorine-rich fluoride, K₃Ba₂Zr₆F₃₁, was synthesized by coupling the ZrF₈ group, featuring acentric cis-[Zr₆F₃₄]¹⁰⁻ clusters with a 6₃-screw axis. Significantly, K₃Ba₂Zr₆F₃₁ exhibits a short UV cutoff edge (below 200 nm) and moderate second-harmonic generation (SHG) response (0.5 × KH₂PO₄). It also possesses a relatively large birefringence (0.08@1064 nm), together with a broad transparency window (2.5–21.1 μm). First-principles calculations suggest that the cis-[Zr₆F₃₄]¹⁰⁻ cluster built by ZrF₈ dodecahedra are the dominant contributors to the large band gap (7.89 eV, cal.) and SHG response simultaneously. Such systematic work highlights that Zr-based fluorides afford a new paradigm for the development of efficient NLO materials with a short UV cutoff edge.