Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States.
Nano Lett. 2018 Jun 13;18(6):3893-3900. doi: 10.1021/acs.nanolett.8b01235. Epub 2018 May 25.
We present a spectroscopic study of colloidal PbSe quantum dots (QDs) that have been photodoped to introduce excess delocalized conduction-band (CB) electrons. High-quality absorption spectra are obtained for these degenerately doped QDs with excess electron concentrations up to ∼10 cm. At the highest doping levels, electrons have completely filled the 1S orbitals of the CB and partially populated the higher-energy 1P orbitals. Spectroscopic changes observed as a function of carrier concentration permit an unambiguous assignment of the second excitonic absorption maximum to 1P-1P transitions. At intermediate doping levels, a clear absorption feature appears between the first two excitonic maxima that is attributable to parity-forbidden 1S-1P excitations, which become observable because of electrostatic symmetry breaking. Redshifts of the main excitonic absorption features with increased carrier concentration are also analyzed. The Coulomb stabilization energies of both the 1S-1S and 1P-1P excitons in n-doped PbSe QDs are remarkably similar to those observed for multiexcitons with the same electron count. The origins of these redshifts are discussed.
我们对胶体 PbSe 量子点（QD）进行了光谱研究，这些量子点已经被光掺杂以引入多余的离域导带（CB）电子。对于这些简并掺杂的 QD，我们获得了高质量的吸收光谱，其多余电子浓度高达约 10 cm。在最高掺杂水平下，电子完全填充了 CB 的 1S 轨道，并部分填充了更高能量的 1P 轨道。随着载流子浓度的变化观察到的光谱变化允许将第二个激子吸收最大值明确分配给 1P-1P 跃迁。在中间掺杂水平下，在第一个和第二个激子最大值之间出现了一个明显的吸收特征，这归因于宇称禁戒的 1S-1P 激发，由于静电对称破缺，这些激发变得可见。随着载流子浓度的增加，主要激子吸收特征的红移也进行了分析。n 掺杂 PbSe QD 中 1S-1S 和 1P-1P 激子的库仑稳定能与具有相同电子数的多激子观察到的稳定能非常相似。讨论了这些红移的起源。
