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, Li-7(TeO3)(3)F (P6(3)), 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 psi-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 x KH2PO4 @1064 nm, 0.2 x beta-BaB2O4 @532 nm) and a large laser damage threshold (73 x AgGaS2). Furthermore, theoretical calculations reveal that the LiO4 and LiO3F tetrahedra also contribute significantly to the SHG response (similar to 30%).