期刊
NANO LETTERS
卷 17, 期 12, 页码 7487-7493出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b03399
关键词
Colloidal quantum dots; single-dot spectroscopy; exciton; charge states; quantum efficiency; absorption cross section
类别
资金
- National Natural Science Foundation of China [11474114, 21573194]
- Thousand-Young Talent Program of China
- National Key Research and Development Program of China [2016YFB0401600]
- Huazhong University of Science and Technology
Upon photo- or electrical-excitation, colloidal quantum dots (QDs) are often found in multicarrier states due to multiphoton absorption, photocharging, or imbalanced carrier injection of the QDs. While many of these multicarrier states are observed in single-dot spectroscopy, their properties are not well studied due to random charging/discharging, emission intensity intermittency, and uncontrolled surface defects of single QDs. Here we report in situ deciphering of the charging status, precisely assessing the absorption cross section, and determining the absolute emission quantum yield of monoexciton and biexciton states for neutral, positively charged, and negatively charged single core/shell CdSe/CdS QDs. We uncover very different photon statistics of the three charge states in single QDs and unambiguously identify their charge signs together with the information on their photoluminescence decay dynamics. We then show their distinct photoluminescence saturation behaviors and evaluate the absolute values of absorption cross sections and quantum efficiencies of monoexcitons and biexcitons. We demonstrate that the addition of an extra hole or electron in a QD not only changes its emission properties but also varies its absorption cross section.
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