Spin-flip limited exciton dephasing in CdSe/ZnS colloidal quantum dots.

نویسندگان

  • Francesco Masia
  • Nicolò Accanto
  • Wolfgang Langbein
  • Paola Borri
چکیده

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.

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عنوان ژورنال:
  • Physical review letters

دوره 108 8  شماره 

صفحات  -

تاریخ انتشار 2012