Discovering alternative means to control electronic states in semiconductor nanostructures is the key to the development of new quantum technologies. Controlling the cyclotron motion of free charge carriers in semiconductor nanocrystals using an external magnetic field generates a tunable angular momentum, as a collective electronic degree of freedom, which can be imparted to the electronic band states to achieve complete exciton polarization. The sign of this polarization is determined by the type of majority charge carriers in a given lattice. Using magnetic circular dichroism spectroscopy, we demonstrate a simultaneous polarization of excitonic states in substoichiometric oxygen-deficient CeO_2–x nanocrystals associated with electrons and holes, which can be controlled by the thermal treatment of colloidal nanocrystals in oxidizing or reducing conditions. The presence of both occupied and unoccupied midgap states, due to Ce³⁺ 4f and Ce⁴⁺ 4f orbitals, respectively, allows for selective probing of the effect of holes in the valence band (VB → Ce⁴⁺ 4f) and electrons in the conduction band (Ce³⁺ 4f → CB). The two transitions show the opposite sign at 300 K due to the opposite angular momenta associated with cyclotron electrons and holes. The ability to manipulate Ce 4f-derived midgap states by defect formation during the synthesis or postsynthesis treatment allows for a range of new technological applications of CeO_2–x nanocrystals in optoelectronics.

中文翻译：

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基于缺陷的氧化还原过程控制双极 CeO2–x 纳米晶体中的双激子极化


发现控制半导体纳米结构中电子态的替代方法是开发新量子技术的关键。使用外部磁场控制半导体纳米晶体中自由载流子的回旋运动会产生可调角动量，作为集体电子自由度，可以将其赋予电子带态以实现完全激子极化。这种极化的符号由给定晶格中多数电荷载流子的类型决定。利用磁性圆二色光谱，我们证明了亚化学计量缺氧 CeO _2–x 纳米晶体中与电子和空穴相关的激子态的同时极化，这可以通过在氧化或还原条件下对胶体纳米晶体进行热处理来控制。分别由于 Ce ³⁺ 4f 和 Ce ⁴⁺ 4f 轨道而存在占据和未占据的中带隙态，允许选择性探测价带中空穴的影响（VB → Ce ⁴⁺ 4f) 和导带中的电子 (Ce ³⁺ 4f → CB)。由于与回旋加速器电子和空穴相关的相反角动量，这两个跃迁在 300 K 处显示出相反的符号。在合成或合成后处理过程中通过缺陷形成来操纵 Ce 4f 衍生的中带隙态的能力允许 CeO _2–x 纳米晶体在光电子学中的一系列新技术应用。