Photodoping and Transient Spectroscopies of Copper-Doped CdSe/CdS Nanocrystals.
basic_science · Level V
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- Record sourced from PubMed, PMID 29286633.
- Also identified by DOI 10.1021/acsnano.7b07879.
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Abstract
Colloidal Cu<sup>+</sup>-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<sup>+</sup>: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 (ML<sub>CB</sub>CT) absorption band and also reveal a photoinduced midgap valence-band (VB)-to-copper charge-transfer (L<sub>VB</sub>MCT) 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 ML<sub>CB</sub>CT excited state is still formed upon photoexcitation of the n-doped Cu<sup>+</sup>: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.