Alkali-metal rare-earth carbonates (ARECs) find great potential in nonlinear optical applications. As the most common method, the hydrothermal reaction is widely used in synthesizing ARECs. The black-box nature of the hydrothermal reaction makes it difficult for understanding the formation processes and therefore may slow down the pace of structural discovery. Here, by simply soaking the rare-earth carbonates in Na₂CO₃ solutions, we successfully obtain a series of noncentrosymmetric Na₃RE(CO₃)₃·6H₂O (RE = Tb 1, Sm 2, Eu 3, Gd 4, Dy 5, Ho 6, and Er 7) compounds without using the high-temperature hydrothermal method. The transformation process, investigated by powder X-ray diffraction and scanning electron microscopy, is governed by the concentration of the soaking solutions. Na₃Tb(CO₃)₃·6H₂O, as an example, is studied structurally, and its physical properties are characterized. It exhibits a second harmonic generation effect of 0.5 × KDP and a short UV cutoff edge of 222 nm (5.8 eV). Our study provides insights for exploring new AREC structures, which may further advance the development of carbonate nonlinear optical crystals.

中文翻译：

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浸泡稀土碳酸盐进行改变：探索碳酸盐非线性光学晶体的替代方法

碱金属稀土碳酸盐（AREC）在非线性光学应用中具有巨大潜力。水热反应作为最常见的方法，广泛应用于合成ARECs。水热反应的黑箱性质使得理解形成过程变得困难，因此可能会减慢结构发现的步伐。这里，通过简单地将稀土碳酸盐浸泡在Na ₂ CO ₃溶液中，我们成功地获得了一系列非中心对称的Na ₃ RE(CO ₃ ) ₃ ·6H ₂ O (RE = Tb 1 , Sm 2 , Eu 3 , Gd 4、Dy 5、Ho 6和Er 7）化合物，无需使用高温水热法。通过粉末 X 射线衍射和扫描电子显微镜研究的转变过程由浸泡溶液的浓度控制。以Na ₃ Tb(CO ₃ ) ₃ ·6H ₂ O为例，对其结构进行了研究，并表征了其物理性能。它具有 0.5 × KDP 的二次谐波产生效应和 222 nm (5.8 eV) 的短 UV 截止边缘。我们的研究为探索新的AREC结构提供了见解，这可能会进一步推动碳酸盐非线性光学晶体的发展。