title: Spin-flip limited exciton dephasing in CdSe/ZnS colloidal quantum dots.
abstract: The dephasing time of the lowest bright exciton in CdSe/ZnS wurtzite quantum dots is measured from 5 to 170 K and compared with density dynamics within the exciton fine structure using a sensitive three-beam four-wave-mixing technique unaffected by spectral diffusion. Pure dephasing via acoustic phonons dominates the initial dynamics, followed by an exponential zero-phonon line dephasing of 109 ps at 5 K, much faster than the ~10 ns exciton radiative lifetime. The zero-phonon line dephasing is explained by phonon-assisted spin flip from the lowest bright state to dark-exciton states. This is confirmed by the temperature dependence of the exciton lifetime and by direct measurements of the bright-dark-exciton relaxation. Our results give an unambiguous evidence of the physical origin of the exciton dephasing in these nanocrystals.
authors.affiliation: Cardiff University School of Physics and Astronomy, The Parade, Cardiff, United Kingdom.
authors.forename: Francesco
authors.initials: F
authors.lastname: Masia
authors.forename: Nicolò
authors.initials: N
authors.lastname: Accanto
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Langbein
authors.forename: Paola
authors.initials: P
authors.lastname: Borri