Chemical substitution towards a rare-earth borate deep ultraviolet NLO crystal exhibiting a strong SHG response

The fabrication of nonlinear optical (NLO) materials that exhibits both pronounced second harmonic generation (SHG) response and broad ultraviolet (UV) transmission range remains a big challenge. In this study, we employed a flux method to extract a potential rare-earth borate UV NLO crystal, K7.5Lu2.5B15O30, by chemical cosubstitution strategy. The title compound crystallizes into a trigonal space group R32 with a three-dimensional structural framework consisting of [B5O10] and [LuO6] groups. Remarkably, K7.5Lu2.5B15O30 possesses a notably short cutoff edge of 198 nm and a wide band gap of 6.3 eV. Moreover, it demonstrates a strong phase-matched SHG efficiency of 1.2×KDP, which represents an optimal balance between a strong NLO effect and a wide UV transmission range. Besides, theoretical calculations and structural analyses unveil that the NLO properties observed in K7.5Lu2.5B15O30 are primarily attributable to the synergistic effect of the [B5O10] groups and [LuO6] octahedra. These findings indicate that K7.5Lu2.5B15O30 has potential applications as beryllium-free UV NLO materials