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Model-independent determination of the carrier multiplication time constant in CdSe nanocrystals

Califano, M. (2009) Model-independent determination of the carrier multiplication time constant in CdSe nanocrystals. Physical Chemistry Chemical Physics, 11 (43). pp. 10180-10184. ISSN 1463-9076


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The experimental determination of the carrier multiplication (CM) time constant is complicated by the fact that this process occurs within the initial few hundreds of femtoseconds after excitation and, in transient-absorption experiments, cannot be separated from the buildup time of the 1p-state population. This work provides an accurate theoretical determination of the electron relaxation lifetime during the last stage of the p-state buildup, in CdSe nanocrystals, in the presence of a single photogenerated hole (no CM) and of a hole plus an additional electron–hole pair (following CM). From the invariance of the 1p buildup time observed experimentally for excitations above and below the CM threshold producing hot carriers with the same average per-exciton excess energy, and the calculated corresponding variations in the electron decay time in the two cases, an estimate is obtained for the carrier multiplication time constant. Unlike previous estimates reported in the literature so far, this result is model-independent, i.e., is obtained without making any assumption on the nature of the mechanism governing carrier multiplication. It is then compared with the time constant calculated, as a function of the excitation energy, assuming an impact-ionization-like process for carrier multiplication (DCM). The two results are in good agreement and show that carrier multiplication can occur on timescales of the order of tens of femtoseconds at energies close to the observed onset. These findings, which are compatible with the fastest lifetime estimated experimentally, confirm the suitability of the impact-ionization model to explain carrier multiplication in CdSe nanocrystals.

Item Type: Article
Copyright, Publisher and Additional Information: © Royal Society of Chemistry 2009. This is an author produced version of a paper published in 'PCCP'. Uploaded in accordance with the publisher's self-archiving policy.
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Engineering (Leeds) > School of Electronic & Electrical Engineering (Leeds) > Institute of Microwaves and Photonics (Leeds)
Depositing User: Repository Officer
Date Deposited: 08 Dec 2009 16:40
Last Modified: 08 Feb 2013 17:06
Published Version: http://dx.doi.org/10.1039/b908028g
Status: Published
Publisher: Royal Society of Chemistry Publishing
Refereed: Yes
Identification Number: 10.1039/b908028g
URI: http://eprints.whiterose.ac.uk/id/eprint/10236

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