School of Physics, Huazhong University of Science and Technology , Luoyu Road 1037, Wuhan 430074, People's Republic of China.
Center for Chemistry of Novel & High-Performance Materials, Department of Chemistry, Zhejiang University , Hangzhou 310027, China.
Nano Lett. 2017 Dec 13;17(12):7487-7493. doi: 10.1021/acs.nanolett.7b03399. Epub 2017 Nov 29.
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.
在光或电激发下，由于多光子吸收、光电荷或 QD 的载流子不平衡注入，胶体量子点 (QD) 通常处于多载流子态。虽然在单点光谱中观察到许多这些多载流子态，但由于单 QD 的随机充电/放电、发射强度间歇性和不受控制的表面缺陷，它们的性质尚未得到很好的研究。在这里，我们报告了对充电状态的原位解读，精确评估了吸收截面，并确定了中性、正电荷和负电荷单个核/壳 CdSe/CdS QD 中单激子和双激子态的绝对发射量子产率。我们在单个 QD 中揭示了这三种电荷状态非常不同的光子统计特性，并明确识别了它们的电荷符号以及它们的光致发光衰减动力学信息。然后，我们展示了它们不同的光致发光饱和行为，并评估了单激子和双激子的吸收截面和量子效率的绝对值。我们证明，在 QD 中添加一个额外的空穴或电子不仅会改变其发射特性，还会改变其吸收截面。
