Magic-sized clusters represent materials with unique properties at the border between molecules and solids and provide important insights into the nanocrystal formation process. However, synthesis, doping, and especially structural characterization become more and more challenging with decreasing cluster size. Herein, we report the successful introduction of Co²⁺ ions into extremely small-sized CdSe clusters with the intention of using internal ligand field transitions to obtain structural insights. Despite the huge mismatch between the radii of Cd²⁺ and Co²⁺ ions (>21%), CdSe clusters can be effectively synthesized with a high Co²⁺ doping concentration of ∼10%. Optical spectroscopy and mass spectrometry suggest that one or two Co²⁺ ions are substitutionally embedded into (CdSe)₁₃ clusters, which is known as one of the smallest CdSe clusters. Using magnetic circular dichroism spectroscopy on the intrinsic ligand field transitions between the different 3d orbitals of the transition metal dopants, we demonstrate that the Co²⁺ dopants are embedded on pseudotetrahedral selenium coordinated sites despite the limited number of atoms in the clusters. A significant shortening of Co–Se bond lengths compared to bulk or nanocrystals is observed, which results in the metastability of Co²⁺ doping. Our results not only extend the doping chemistry of magic-sized semiconductor nanoclusters, but also suggest an effective method to characterize the local structure of these extremely small-sized clusters.

中文翻译：

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魔术尺寸的CdSe团簇的Co ²⁺掺杂：通过配体场跃迁的结构见解。

魔术大小的簇代表了在分子和固体之间的边界处具有独特属性的材料，并为纳米晶体的形成过程提供了重要的见识。然而，随着簇尺寸的减小，合成，掺杂，尤其是结构表征变得越来越具有挑战性。本文中，我们报道了将Co ²⁺离子成功引入极小尺寸的CdSe团簇中的意图，目的是使用内部配体场跃迁获得结构见解。尽管Cd ²⁺和Co ²⁺离子的半径之间存在巨大的不匹配（> 21％），但是可以以大约10％的高Co ²⁺掺杂浓度有效地合成CdSe团簇。光谱学和质谱学表明一或两个钴²⁺离子被替代嵌入到（CdSe）_13个簇中，这被称为最小的CdSe簇之一。在过渡金属掺杂剂的不同3d轨道之间使用固有的配体场跃迁的磁性圆二色光谱，我们证明了尽管簇中原子数量有限，但Co ²⁺掺杂剂仍嵌入在伪四面体硒配位位点上。与块状或纳米晶体相比，Co-Se键的长度显着缩短，这导致了Co ²⁺的亚稳性。掺杂。我们的结果不仅扩展了魔术尺寸的半导体纳米簇的掺杂化学，而且还提出了一种表征这些极小尺寸簇的局部结构的有效方法。