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Open AccessArticle

Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study

1
Theoretical Physical Chemistry, Research Unit Molecular Systems, University of Liege, 4000 Liege, Belgium
2
Department of Chemistry, University of Padova, via Marzolo, 1, 35131 Padova, Italy
3
The Fritz Haber Research Center, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
4
Department of Molecular and Medical Pharmacology, David Geffen School of Medicine and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90005, USA
*
Author to whom correspondence should be addressed.
Appl. Sci. 2020, 10(4), 1328; https://doi.org/10.3390/app10041328
Received: 20 January 2020 / Revised: 10 February 2020 / Accepted: 11 February 2020 / Published: 15 February 2020
(This article belongs to the Special Issue State of the Art of Nanosciences in Belgium)
Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.
Keywords: exciton dynamics; CdSe quantum dots dimers; size dispersion effects; coherent electronic dynamics; pump-probe transient absorption spectroscopy exciton dynamics; CdSe quantum dots dimers; size dispersion effects; coherent electronic dynamics; pump-probe transient absorption spectroscopy
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MDPI and ACS Style

Gattuso, H.; Fresch, B.; Levine, R.D.; Remacle, F. Coherent Exciton Dynamics in Ensembles of Size-Dispersed CdSe Quantum Dot Dimers Probed via Ultrafast Spectroscopy: A Quantum Computational Study. Appl. Sci. 2020, 10, 1328.

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