Rational structural design and modification based on known compounds is an effective strategy to explore new nonlinear optical (NLO) materials. Here, three new rare-earth (RE) oxythiogermanates Eu₁₈Ge₉O₅S₃₁ (1), Ca_3.32Eu_14.68Ge₉O₅S₃₁ (2) and Ba₃Eu₁₅Ge₉O₅S₃₁ (3) were obtained by the novel cation and anion co-partial substitution strategy from the parent β-Eu₂GeS₄ (0), which induces centrosymmetric to noncentrosymmetric (NCS) structural transformation and NLO activities. They crystallize with a pseudo-zero dimensional structure in the chiral R3 space group, featuring almost linearly arranged isolated GeS₄ and GeOS₃ tetrahedra. Their optical band gaps were determined to be 2.18, 2.23 and 2.24 eV, respectively. 1 and 2 show balanced NLO properties with moderate second-harmonic generation (SHG) responses (0.5 and 0.6 × AGS) and high laser-induced damage thresholds (LIDTs) (3.3 × AGS). Moreover, theoretical calculations show that their NLO properties are determined by the synergistic effect of GeS₄ and GeOS₃ tetrahedra. This work enriches the chemistry of rarely studied RE oxychalcogenides and provides a fresh route for designing NCS structures targeting diverse applications.

中文翻译：

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阳离子和阴离子共部分取代诱导中心对称到非中心对称结构转变构建非线性光学稀土硫代锗酸盐


基于已知化合物的合理结构设计和修饰是探索新型非线性光学（NLO）材料的有效策略。这里，三种新的稀土 (RE) 硫代锗酸盐 Eu ₁₈ Ge ₉ O ₅ S ₃₁ (1)、Ca _3.32 Eu _14.68 Ge ₉ O ₅ S ₃₁ (2) 和 Ba ₃ Eu ₁₅ Ge ₉ O ₅ S ₃₁ (3) 通过新型阳离子和阴离子共部分取代策略从母体获得β-Eu ₂ GeS ₄ (0)，诱导中心对称到非中心对称 (NCS) 结构转变和 NLO 活性。它们在手性 R3 空间群中结晶，具有伪零维结构，具有几乎线性排列的孤立的 GeS ₄ 和 GeOS ₃ 四面体。它们的光学带隙分别确定为2.18、2.23和2.24 eV。图 1 和图 2 显示了平衡的 NLO 特性，具有中等的二次谐波产生 (SHG) 响应（0.5 和 0.6 × AGS）以及高激光诱导损伤阈值 (LIDT)（3.3 × AGS）。此外，理论计算表明它们的非线性光学性质是由GeS ₄ 和GeOS ₃ 四面体的协同效应决定的。这项工作丰富了很少研究的稀土硫族化物的化学性质，并为设计针对不同应用的 NCS 结构提供了一条新途径。