title: Ultrafast Charge Dynamics in Trap-Free and Surface-Trapping Colloidal Quantum Dots.
abstract: Ultrafast transient absorption spectroscopy is used to study subnanosecond charge dynamics in CdTe colloidal quantum dots. After treatment with chloride ions, these can become free of surface traps that produce nonradiative recombination. A comparison between these dots and the same dots before treatment enables new insights into the effect of surface trapping on ultrafast charge dynamics. The surface traps typically increase the rate of electron cooling by 70% and introduce a recombination pathway that depopulates the conduction band minimum of single excitons on a subnanosecond timescale, regardless of whether the sample is stirred or flowed. It is also shown that surface trapping significantly reduces the peak bleach obtained for a particular pump fluence, which has important implications for the interpretation of transient absorption data, including the estimation of absorption cross-sections and multiple exciton generation yields.
authors.affiliation: School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Smith
authors.affiliation: School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK.
authors.forename: Marina A
authors.initials: MA
authors.lastname: Leontiadou
authors.affiliation: School of Chemistry University of Manchester Manchester M13 9PL UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Page
authors.affiliation: School of Chemistry University of Manchester Manchester M13 9PL UK.
authors.forename: Paul
authors.initials: P
authors.lastname: O'Brien
authors.affiliation: School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Binks
keywords: nanocrystals; quantum dots; surface trapping; transient absorption; ultrafast spectroscopy