The systematic modification of the molecular structure of nonlinear optical (NLO)-active materials is a very attractive approach to the improvement of NLO performance. In this study, one lutetium selenite compound Lu(SeO₃)(HSeO₃)(H₂O)·(H₂O) (1) was synthesized by hydrothermal means, while a further two lutetium selenites Lu₃F(SeO₃)₄ (2) and Lu(SeO₃)(NO₃)(H₂O) (3) were successfully synthesized by anion partial substitution (APS) of the parent structure 1 under hydrothermal conditions. Specifically, substitution of the [HSeO₃]^– anions in the noncentrosymmetric 1 by F^– or [NO₃]⁻ anions with differing denticity leads to the formation of polar 2 and centrosymmetric 3. Our study reveals that the denticity of the secondary functional anions has a significant influence on the coordination environments of the rare-earth-metal cation Lu³⁺ and consequently the molecular configuration and NLO performance of the resultant multidimensional selenites. In contrast to 1, which displays a weak second-harmonic generation (SHG) response (0.1 × KH₂PO₄ (KDP)), 2 exhibits a greatly improved NLO performance, including a strong SHG signal (2.5 × KDP, the highest value among rare-earth-metal-based NLO selenites), a wide band gap (3.57 eV) and optical transparency window (0.35–10.3 μm), high thermal stability (∼550 °C), and a large laser damage threshold (36 × AgGaS₂). These results suggest that 2, as the first example of a fluorinated lutetium selenite, is a strong NLO candidate crystal spanning a region from the near-ultraviolet to the mid-infrared. These APS studies highlight a new feasible approach toward high-performance NLO crystals.

中文翻译：

---

单齿阴离子部分取代增强ute亚硒酸盐中二阶光学非线性

非线性光学（NLO）活性材料的分子结构的系统化修改是提高NLO性能的一种非常有吸引力的方法。在这项研究中，通过水热法合成了一种亚硒酸盐化合物Lu（SeO ₃）（HSeO ₃）（H ₂ O）·（H ₂ O）（1），而另外两种two亚硒酸盐Lu ₃ F（SeO ₃）₄（2）和Lu（SeO ₃）（NO ₃）（H ₂ O）（3）通过母体结构1的阴离子部分取代（APS）成功合成在热液条件下。具体地，[HSeO取代₃ ] ^-的阴离子的非中心对称1被F ^-或[NO ₃ ] ^-具有不同齿合度导致的极性形成的阴离子2和中心对称3。我们的研究表明，次要功能阴离子的密度对稀土金属阳离子Lu ³⁺的配位环境具有重要影响，因此对所得多维亚硒酸盐的分子构型和NLO性能也有重要影响。与1相比，它显示出较弱的二次谐波生成（SHG）响应（0.1×KH₂ PO ₄（KDP）），2的NLO性能大大提高，包括较强的SHG信号（2.5×KDP，是稀土金属NLO亚硒酸盐中的最高值），宽带隙（3.57 eV）和光学透明窗（0.35-10.3μm），高热稳定性（〜550°C）和较大的激光损伤阈值（36×AgGaS ₂）。这些结果表明，2作为氟化se亚硒酸盐的第一个实例，是一种强NLO候选晶体，横跨从近紫外线到中红外的区域。这些APS研究突显了一种针对高性能NLO晶体的新可行方法。