title: Engineering the spin-flip limited exciton dephasing in colloidal CdSe/CdS quantum dots.
abstract: We have measured the intrinsic exciton dephasing in high-quality zinc blende CdSe/CdS colloidal quantum dots in the temperature range from 5 to 170 K using a sensitive three-beam photon echo technique in heterodyne detection, which is not affected by spectral diffusion. Pure dephasing via acoustic phonons dominates the initial dynamics, followed by an exponential zero-phonon line dephasing. From the temperature dependence of the zero-phonon line dephasing, the exciton lifetime, and the exciton thermalization within its fine structure, we show that the zero-phonon line dephasing of the lowest bright state originates from the phonon-assisted spin-flip to dark exciton states. Importantly, we can control the dephasing by tailoring the exciton fine structure through its dependence on the dot core size and shell thickness, as expected from the spin-flip mechanism. By reducing the electron-hole exchange interaction with increasing core size and delocalization of the electron wave function in the quasi-type-II core/shell band alignment, we find the longest zero-phonon line dephasing time of ∼110 ps at 5 K in dots with the largest core diameter (5.7 nm) and the thickest CdSe shell (9 monolayers) in the series studied.
authors.affiliation: School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, United Kingdom.
authors.forename: Nicolò
authors.initials: N
authors.lastname: Accanto
authors.forename: Francesco
authors.initials: F
authors.lastname: Masia
authors.forename: Iwan
authors.initials: I
authors.lastname: Moreels
authors.forename: Zeger
authors.initials: Z
authors.lastname: Hens
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Langbein
authors.forename: Paola
authors.initials: P
authors.lastname: Borri
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D008422:Materials Testing; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D013113:Spin Labels; D013440:Sulfides / Q000737:chemistry*; D013696:Temperature
chemical_list: D019187:Cadmium Compounds; D003102:Colloids; D018036:Selenium Compounds; D013113:Spin Labels; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide