title: Dynamics of Intraband and Interband Auger Processes in Colloidal Core-Shell Quantum Dots.
abstract: Conventional colloidal quantum dots (QDs) suffer from rapid energy losses by nonradiative (Auger) processes, leading to sub-ns lifetimes in all excited states but the lowest-energy single exciton. Suppression of interband Auger decay, such as biexciton Auger recombination, has been achieved with the design of heterostructured core-shell QDs. Auger-like processes are also believed to be responsible for rapid intraband hot-electron cooling in QDs. However, the simultaneous effect of shell growth on interband Auger recombination and intraband hot-electron cooling has not been addressed. Here we investigate how the growth of a CdS shell affects these two relaxation processes in CdSe/CdS core-shell QDs. Using a combination of ultrafast pump-push-probe spectroscopy on the QD ensemble and analysis of the photon statistics from single QDs, we find that Auger losses in the biexciton state are suppressed with increasing shell thickness, while hot-electron cooling remains unaffected. Calculations conducted within an eight-band k·p model confirm the experimental dependence of the biexciton Auger decay on the shell thickness, and provide insights into the factors determining the cooling rate of hot carriers.
authors.affiliation: Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science , Princetonplein 1, 3584 CC Utrecht, The Netherlands.
authors.forename: Freddy T
authors.initials: FT
authors.lastname: Rabouw
authors.affiliation: Technion - Israel Institute of Technology , Haifa 32000, Israel.
authors.forename: Roman
authors.initials: R
authors.lastname: Vaxenburg
authors.affiliation: Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 OHE, U.K.|FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Artem A
authors.initials: AA
authors.lastname: Bakulin
authors.affiliation: Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science , Princetonplein 1, 3584 CC Utrecht, The Netherlands.
authors.forename: Relinde J A
authors.initials: RJ
authors.lastname: van Dijk-Moes
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: Huib J
authors.initials: HJ
authors.lastname: Bakker
authors.affiliation: Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia.
authors.forename: Anna
authors.initials: A
authors.lastname: Rodina
authors.affiliation: Technion - Israel Institute of Technology , Haifa 32000, Israel.
authors.forename: Efrat
authors.initials: E
authors.lastname: Lifshitz
authors.affiliation: Naval Research Laboratory , Washington, D.C. 20375, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: L Efros
authors.affiliation: FOM Institute AMOLF , Science Park 104, 1098 XG Amsterdam, The Netherlands.
authors.forename: A Femius
authors.initials: AF
authors.lastname: Koenderink
authors.affiliation: Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science , Princetonplein 1, 3584 CC Utrecht, The Netherlands.
authors.forename: Daniël
authors.initials: D
authors.lastname: Vanmaekelbergh
keywords: Auger processes; k·p theory; quantum dots; single quantum dot spectroscopy; transient absorption