Ion-induced structural and optical performance evolution in LBO-like crystals: experimental and theoretical investigation

Abstract

A new alkali metal borate fluoride Li₃KB₉O₁₅F has been successfully obtained by the high-temperature solution method in open air for the first time. An X-ray crystallographic study reveals that it crystallizes in the trigonal space group R3c (no. 161), a = 11.974(4) Å, b = 11.974(4) Å, c = 15.998(11) Å and Z = 6. It exhibits a complicated three-dimensional (3D) network composed of LiO₃F, KO₆F distorted polyhedra and 3D B–O framework. Its UV cut-off edge is below 175 nm. Interestingly, for the crystal structure of LiB₃O₅, as K⁺ and F⁻ are introduced in the structure, a new Li₃KB₉O₁₅F compound is obtained. The structural comparison between LiB₃O₅ and Li₃KB₉O₁₅F and the changes in performance caused by the introduction of ions are discussed. The electronic structures and the optical properties have been evaluated using the first-principles methods. After carefully checking the density of the B–O groups and the bandgap, the authors found that the denser B–O groups per unit cell would lead to a deeper UV cutoff edge, which is beneficial for designing novel UV/DUV NLO compounds.