Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
ACS Nano. 2018 Jan 23;12(1):718-728. doi: 10.1021/acsnano.7b07879. Epub 2018 Jan 5.
Colloidal Cu-doped CdSe/CdS core/shell semiconductor nanocrystals (NCs) are investigated in their as-prepared and degenerately n-doped forms using time-resolved photoluminescence and transient-absorption spectroscopies. Photoluminescence from Cu:CdSe/CdS NCs is dominated by recombination of delocalized conduction-band (CB) electrons with copper-localized holes. In addition to prominent bleaching of the first excitonic absorption feature, transient-absorption measurements show bleaching of the sub-bandgap copper-to-CB charge-transfer (MLCT) absorption band and also reveal a photoinduced midgap valence-band (VB)-to-copper charge-transfer (LMCT) absorption band that extends into the near-infrared, as predicted by recent computations. The photoluminescence of these NCs is substantially diminished upon introduction of excess CB electrons via photodoping. Time-resolved photoluminescence measurements reveal that the MLCT excited state is still formed upon photoexcitation of the n-doped Cu:CdSe/CdS NCs, but its luminescence is quenched by a fast (picosecond) three-carrier trap-assisted Auger recombination process involving two CB electrons and one copper-bound hole.
胶体铜掺杂的 CdSe/CdS 核/壳半导体纳米晶体（NCs）在其未经处理和退化 n 型掺杂的形式下，使用时间分辨光致发光和瞬态吸收光谱进行了研究。Cu：CdSe/CdS NCs 的光致发光主要由离域导带（CB）电子与铜定域空穴的复合决定。除了第一个激子吸收特征的明显漂白外，瞬态吸收测量还显示了带隙下铜到 CB 电荷转移（MLCT）吸收带的漂白，并且还揭示了一个光诱导的中间价带（VB）到铜电荷转移（LMCT）吸收带，该吸收带延伸到近红外，正如最近的计算所预测的那样。通过光掺杂引入过量的 CB 电子后，这些 NCs 的光致发光大大降低。时间分辨光致发光测量表明，在 n 型掺杂的 Cu：CdSe/CdS NCs 的光激发下，仍然形成了 MLCT 激发态，但由于涉及两个 CB 电子和一个铜结合空穴的快速（皮秒）三载流子陷阱辅助俄歇复合过程，其发光被猝灭。
