Li 7 (TeO 3 ) 3 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 TeO3 group afforded the first lithium fluoride tellurite, namely, Li7 (TeO3 )3 F (P63 ), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [Li7 O9 F]12- composed of LiO3 F 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 × KH2 PO4 @1064 nm, 0.2 × β-BaB2 O4 @532 nm) and a large laser damage threshold (73 × AgGaS2 ). Furthermore, theoretical calculations reveal that the LiO4 and LiO3 F tetrahedra also contribute significantly to the SHG response (∼30%).