title: Multiple exciton generation and ultrafast exciton dynamics in HgTe colloidal quantum dots.
abstract: The investigation of sub-nanosecond exciton dynamics in HgTe colloidal quantum dots using ultrafast transient absorption spectroscopy is reported. The transmittance change spectrum acquired immediately after pumping is dominated by a bleach blue-shifted by ~200-300 nm from the photoluminescent emission band. Comparison with a tight-binding model of the electronic structure allows this feature to be attributed to the filling of band edge states. The form of the pump-induced transmittance transients is dependent on the excitation rate and the rate of sample stirring. For moderate pumping of stirred samples, the transmittance transients are well-described by a mono-exponential decay associated with biexciton recombination, with a lifetime of 49 ± 2 ps. For samples that are strongly-pumped or unstirred, the decay becomes bi-exponential in form, indicating that trap-related recombination has become significant. We also present a new analysis that enables fractional transmittance changes to be related to band edge occupation for samples with arbitrary optical density at the pump wavelength. This allows us to identify the occurrence of multiple exciton generation, which results in a quantum yield of 1.36 ± 0.04 for a photon energy equivalent to 3.1 times the band gap, in good agreement with the results of the model.
authors.affiliation: School of Physics and Astronomy & Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK. david.binks@manchester.ac.uk.
authors.forename: Ali
authors.initials: A
authors.lastname: Al-Otaify
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Kershaw
authors.forename: Shuchi
authors.initials: S
authors.lastname: Gupta
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Rogach
authors.forename: Guy
authors.initials: G
authors.lastname: Allan
authors.forename: Christophe
authors.initials: C
authors.lastname: Delerue
authors.forename: David J
authors.initials: DJ
authors.lastname: Binks