Mid-infrared (IR) nonlinear optical (NLO) materials have generated extensive research interest because of their crucial role in laser technology applications. Here, we report the synthesis of a novel cadmium germanate NLO crystal, K₄Cd₃Ge₄O₁₃, using spontaneous crystallization. K₄Cd₃Ge₄O₁₃ demonstrates a distinct three-dimensional structural framework characterized by twisted [Ge₄O₁₃] and [Cd₃O₁₀] clusters, composed of [GeO₄], [CdO₄], [CdO₅], and [CdO₆] basic building units, respectively, which represents an unprecedented structural feature. The title compound undergoes a desirable congruent melting behavior at about 727 °C. Notably, K₄Cd₃Ge₄O₁₃ demonstrates a short UV cutoff edge at 261 nm, coupled with a wide energy gap of 4.4 eV, and maintains an extended IR transparency window at around 6.0 μm. More importantly, it demonstrates a strong second-harmonic generation activity comparable to that of KH₂PO₄ (KDP) at 1064 nm. Theoretical analyses further elucidate that the remarkable optical performances of K₄Cd₃Ge₄O₁₃ are predominantly attributed to the cooperative effects of Ge–O and Cd–O bond-based motifs. These desired characteristics underscore the potential of K₄Cd₃Ge₄O₁₃ as a good candidate material for mid-IR NLO applications.

中文翻译：

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K4Cd3Ge4O13： 一种同余熔融锗酸盐非线性光学晶体，具有适度的二次谐波产生强度和宽透明窗口


中红外 （IR） 非线性光学 （NLO） 材料因其在激光技术应用中的关键作用而引起了广泛的研究兴趣。在这里，我们报道了使用自发结晶合成一种新型锗酸镉 NLO 晶体 K₄Cd₃Ge₄O₁₃。K₄Cd₃Ge₄O₁₃ 展示了一个独特的三维结构框架，其特征是扭曲的 [Ge₄O₁₃] 和 [Cd₃O₁₀] 集群，分别由 [GeO₄]、[CdO₄]、[CdO₅] 和 [CdO₆] 基本建筑单元组成，代表了前所未有的结构特征。标题化合物在大约 727 °C 时发生理想的一致熔融行为。 值得注意的是，K₄Cd₃Ge₄O₁₃ 在 261 nm 处表现出较短的紫外截止边缘，再加上 4.4 eV 的宽能隙，并在 6.0 μm 左右保持扩展的红外透明窗口。更重要的是，它在 1064 nm 处表现出与 KH₂PO₄ （KDP） 相当的强二次谐波产生活性。理论分析进一步阐明，K₄Cd₃Ge₄O₁₃ 的显着光学性能主要归因于 Ge-O 和 Cd-O 键基序的协同效应。这些理想的特性强调了 K₄Cd₃Ge₄O₁₃ 作为中红外 NLO 应用的良好候选材料的潜力。