Quantum dots (QDs) form a promising family of nanomaterials for various applications in optoelectronics. Understanding the details of the excited-state dynamics in QDs is vital for optimizing their function. We apply two-color 2D electronic spectroscopy to investigate CdSe QDs at 77 K within a broad spectral range. Analysis of the electronic dynamics during the population time allows us to identify the details of the excitation pathways. The initially excited high-energy electrons relax with the time constant of 100 fs. Simultaneously, the states at the band edge rise within 700 fs. Remarkably, the excited-state absorption is rising with a very similar time constant of 700 fs. This makes us reconsider the earlier interpretation of the excited-state absorption as the signature of a long-lived trap state. Instead, we propose that this signal originates from the excitation of the electrons that have arrived in the conduction-band edge.

Department of Chemistry Technical University of Denmark DK 2800 Kongens Lyngby Denmark

Division of Chemical Physics and NanoLund Lund University P O Box 124 22100 Lund Sweden

ELI Beamlines Institute of Physics Czech Academy of Sciences v v i Za Radnicí 835 252 41 Dolní Břežany Czech Republic

Regional Center for Special Optics and Optoelectronic Systems Institute of Plasma Physics of the Czech Academy of Sciences 270 00 Prague 8 Czech Republic

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