Journal
ACS NANO
Volume 5, Issue 3, Pages 2026-2035Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn2002689
Keywords
transient absorption; photoluminescence upconversion; time-correlated single photon counting; quantum dot; charge carrier trapping; radiative recombination
Categories
Funding
- National Science Foundation [DMR-0520513]
- NSF-NSEC
- NSF-MRSEC
- Keck Foundation
- State of Illinois
- Northwestern University
- Dreyfus Foundation
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A combination of transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopies performed on solution-phase samples of colloidal CdSe quantum dots (QDs) allows the construction of a time-resolved, charge carrier-resolved map of decay from the first excitonic state of the QD. Data from TA and TRPL yield the same six exponential components, with time constants ranging from similar to 1 ps to 50 ns, for excitonic decay. Comparison of TA signals in the visible and near-infrared (NIR) spectral regions enables determination of the relative contributions of electron and hole dynamics to each decay component, and comparison of TA and TRPL reveals that each component represents a competition between radiative and nonradiative decay pathways. In total, these data suggest that the QD sample comprises at least three distinct populations that differ in both the radiative and nonradiative decay pathways available to the excitonic charge carriers, and provide evidence for multiple emissive excitonic states in which the hole is not in the valence band, but rather a relaxed or trapped state.
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