Liu Shaojie, Shu Yufei, Zhu Meiyi, Qin Haiyan, Peng Xiaogang
Key Laboratory of Excited-State Materials of Zhejiang Province and Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
Nano Lett. 2022 Apr 13;22(7):3011-3017. doi: 10.1021/acs.nanolett.2c00220. Epub 2022 Mar 23.
The band-gap energy of most bulk semiconductors tends to increase as the temperature decreases. However, non-monotonic temperature dependence of the emission energy has been observed in semiconductor quantum dots (QDs) at cryogenic temperatures. Here, using stable and highly efficient CdSe/CdS/ZnS QDs as the model system, we quantitatively reveal the origins of the anomalous emission red-shift (∼8 meV) below 40 K by correlating ensemble and single QD spectroscopy measurements. About one-quarter of the anomalous red-shift (∼2.2 meV) is caused by the temperature-dependent population of the band-edge exciton fine levels. The enhancement of electron-optical phonon coupling caused by the increasing population of dark excitons with temperature decreases contributes an ∼3.4 meV red-shift. The remaining ∼2.4 meV red-shift is attributed to temperature-dependent electron-acoustic phonon coupling.
大多数体相半导体的带隙能量往往会随着温度降低而增加。然而，在低温下，半导体量子点（QD）中已观察到发射能量的非单调温度依赖性。在此，我们以稳定且高效的CdSe/CdS/ZnS量子点作为模型系统，通过关联系综和单量子点光谱测量，定量揭示了40K以下异常发射红移（约8meV）的起源。约四分之一的异常红移（约2.2meV）是由带边激子精细能级的温度依赖性占据引起的。随着温度降低，暗激子数量增加导致电子 - 光学声子耦合增强，这贡献了约3.4meV的红移。其余约2.4meV的红移归因于温度依赖性电子 - 声学声子耦合。
