Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe₄ and EuHgSnS₄, containing the “NLO active groups” [HgQ₄]^6– (Q = S, Se) and [GeSe₄]^4–/[SnS₄]^4– were synthesized through traditional high-temperature solid-state reactions. They possess noncentrosymmetric structures, crystallizing in the Ama2 space group, and exhibit strong phase-matchable second-harmonic-generation (SHG) responses (3.1× and 1.77× that of AgGaS₂ for EuHgGeSe₄ and EuHgSnS₄, respectively). Meanwhile, the optical band gaps of EuHgGeSe₄ (1.97 eV) and EuHgSnS₄ (2.14 eV) were determined from UV–vis–NIR diffuse reflectance spectra. Differential scanning calorimetry (DSC) analyses reveal the congruent-melting behavior of EuHgGeSe₄. Furthermore, structural analysis and theoretical calculations verify the critical driving effects of [HgQ₄]^6– tetrahedra on the strong SHG activity. The overall results demonstrate that EuHgGeSe₄ and EuHgSnS₄ are potential IR NLO materials.

中文翻译：

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EuHgGeSe ₄和EuHgSnS ₄：具有强二次谐波响应的两种基于Eu的第四季红外非线性光学材料

金属硫属化物在红外（IR）非线性光学（NLO）领域中起着至关重要的作用。然而，到目前为止，基于Eu的硫族化物型IR NLO材料仍然稀缺。在本文中，两个新的基于Eu的季铵硫属元素EuHgGeSe ₄和EuHgSnS ₄包含“ NLO活性基团” [HgQ ₄ ] ^6–（Q = S，Se）和[GeSe ₄ ] ^4– / [SnS ₄ ] ^4–是通过传统的高温固态反应合成的。它们具有非中心对称的结构，在Ama 2空间群中结晶，并且表现出强的相匹配的二次谐波产生（SHG）响应（AgGaS的3.1X和1.77X）₂为EuHgGeSe ₄和EuHgSnS ₄，分别地）。同时，由紫外可见近红外漫反射光谱确定了EuHgGeSe ₄（1.97 eV）和EuHgSnS ₄（2.14 eV）的光学带隙。差示扫描量热法（DSC）分析揭示了EuHgGeSe _4的全熔融行为。此外，结构分析和理论计算验证了[HgQ ₄ ] ^6–四面体对强SHG活性的关键驱动作用。总体结果表明，EuHgGeSe ₄和EuHgSnS ₄是潜在的IR NLO材料。