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arXiv · 1112.3751

Spin--flip Limited Exciton Dephasing in CdSe/ZnS Colloidal Quantum Dots

Francesco Masia·Nicolò Accanto·Wolfgang Langbein·Paola Borri
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Abstract

The dephasing time of the lowest bright exciton in CdSe/ZnS wurtzite quantum dots is measured from 5 K 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.

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Francesco Masia, Nicolò Accanto, Wolfgang Langbein, Paola Borri. 2011-12-16. Spin--flip Limited Exciton Dephasing in CdSe/ZnS Colloidal Quantum Dots. https://doi.org/10.1103/physrevlett.108.087401

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