We examine the effects of CdS shell growth on photochemical reduction of colloidal CdSe quantum dots (QDs) and describe the spectroscopic properties of the resulting n-type CdSe/CdS QDs. CdS shell growth greatly slows electron trapping. Because of this improvement, complete two-electron occupancy of the 1S_e conduction-band orbital is achieved in CdSe/CdS QDs and found to be much more stable than in past experiments. Simultaneous photoluminescence at two different energies is now observed from QDs possessing two excess conduction-band electrons, reflecting competing recombination of discretized 1S_e and 1P_e conduction-band electrons within photogenerated four-carrier negative tetrons (three electrons and one hole). Stable occupancy of the 1P_e level is not achievable under these conditions, and possible reasons are discussed. The stability and accessibility of these multielectron configurations, and the facile spectroscopic detection of negative tetrons, both make photodoped core/shell QDs attractive for exploring the physical properties of free-standing heavily n-doped colloidal CdSe-based QDs.

中文翻译：

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自由站立的胶态n型CdSe / CdS量子点中的电子稳定性和负四极发光

我们检查了CdS壳生长对胶体CdSe量子点（QDs）的光化学还原的影响，并描述了所得n型CdSe / CdS QD的光谱性质。CdS壳的生长大大减缓了电子捕获。由于此改进，在CdSe / CdS QD中实现了1S _e导带轨道的完全电子占据，并且比过去的实验更稳定。现在，从具有两个过量导带电子的量子点观察到在两种不同能量下的同时光致发光，这反映了离散化的1S _e和1P _e导带电子在光生四载流子负电子中的竞争重组（三个电子和一个空穴）。1P _e的稳定占用在这些条件下无法达到最高水平，并讨论了可能的原因。这些多电子构型的稳定性和可及性，以及简便的光谱检测负向电子，都使光掺杂核/壳量子点对探索自立重掺杂n胶态CdSe胶体量子点的物理性质具有吸引力。