Li₇(TeO₃)₃F: A Lithium Fluoride Tellurite with Large Second Harmonic Generation Responses and a Short Ultraviolet Cutoff Edge

Here, the combination of the strong electropositive lithium and the most electronegative fluorine with the TeO₃ group afforded the first lithium fluoride tellurite, namely, Li₇(TeO₃)₃F (P6₃), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [Li₇O₉F]^12- composed of LiO₃F and LiO₄ tetrahedra with one-dimensional hexagonal tunnels of 12-membered rings along the c-axis, filled by the "isolated" ψ-TeO₃ tetrahedra. Notably, this compound displays the largest band gap of 4.75 eV among all of the non-centrosymmetric metal-tellurites reported so far, as well as strong second harmonic generation (SHG) responses (3 × KH₂PO₄ @1064 nm, 0.2 × β-BaB₂O₄ @532 nm) and a large laser damage threshold (73 × AgGaS₂). Furthermore, theoretical calculations reveal that the LiO₄ and LiO₃F tetrahedra also contribute significantly to the SHG response (∼30%).