The fabrication of nonlinear optical (NLO) materials that exhibit both a pronounced second harmonic generation (SHG) response and a 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, K_7.5Lu_2.5B₁₅O₃₀, by the chemical cosubstitution strategy. The title compound crystallizes in the trigonal space group R32 (no. 155) with a three-dimensional structural framework consisting of [B₅O₁₀] and [LuO₆] groups. Remarkably, K_7.5Lu_2.5B₁₅O₃₀ 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 K_7.5Lu_2.5B₁₅O₃₀ are primarily attributable to the synergistic effect of the [B₅O₁₀] groups and [LuO₆] octahedra. These findings indicate that K_7.5Lu_2.5B₁₅O₃₀ has potential applications as beryllium-free UV NLO materials.

中文翻译：

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对表现出强烈 SHG 响应的稀土硼酸盐紫外线 NLO 晶体的化学取代


制造既具有明显的二次谐波产生 （SHG） 响应又具有较宽紫外线 （UV） 透射范围的非线性光学 （NLO） 材料仍然是一个巨大的挑战。在本研究中，我们采用通量法通过化学共取代策略提取潜在的稀土硼酸盐 UV NLO 晶体 K_7.5Lu_2.5B₁₅O₃₀。标题化合物在三角空间群 R32（编号 155）中结晶，其三维结构框架由 [B₅O₁₀] 和 [LuO₆] 组组成。值得注意的是，K_7.5Lu_2.5B₁₅O₃₀ 具有 198 nm 的明显短截止边缘和 6.3 eV 的宽带隙。此外，它还表现出 1.2 × KDP 的强大相位匹配 SHG 效率，这代表了强大的 NLO 效应和宽紫外线透射范围之间的最佳平衡。此外，理论计算和结构分析表明，在 K_7.5Lu_2.5B₁₅O₃₀ 中观察到的 NLO 特性主要归因于 [B₅O₁₀] 基团和 [LuO₆] 八面体的协同作用。这些结果表明，K_7.5Lu_2.5B₁₅O₃₀ 具有作为无铍 UV NLO 材料的潜在应用。