Li(TeO)F: 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 TeO group afforded the first lithium fluoride tellurite, namely, Li(TeO)F (P6), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [LiOF] composed of LiOF and LiO tetrahedra with one-dimensional hexagonal tunnels of 12-membered rings along the c-axis, filled by the "isolated" ψ-TeO 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 × KHPO @1064 nm, 0.2 × β-BaBO @532 nm) and a large laser damage threshold (73 × AgGaS). Furthermore, theoretical calculations reveal that the LiO and LiOF tetrahedra also contribute significantly to the SHG response (∼30%).