Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 30: POSTER: Chemical physics

CPP 30.4: Poster

Tuesday, March 8, 2005, 16:30–18:30, Poster TU D

Dynamics of Photoinduced Charge Ejection of CdSe Nanocrystals in Dielectric Environments — •Abey Issac¹, F. Cichos², and C. von Borczyskowski¹ — ¹Optical Spectroscopy and Molecular Physics,Center for Nanostructured Materials and Analytics, Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany — ²Photonics and Optical Materials,Center for Nanostructured Materials and Analytics, Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany

Fluorescence intermittency (blinking) of single CdSe/ZnS quantum dots (QDs) obeys power law statistics for the lifetime of the dark states. This power law distribution is supposed to be related to a distribution of states located outside the QDs, which are able to trap charges ejected from the QDs. We present for the first time direct evidence, that blinking is affected by the polarity of the surrounding medium. The higher the dielectric constant of the medium, the higher will be the probability for long off times. To explain the observed results we propose a simple self-trapping model for the ejected charges. The interaction of the reaction field, induced by the ejected charge in the matrix, with the ejected charge stabilizes the charge against a fast return to the ionized particle. On the other hand, the lifetime statistics of the bright periods (on times) is unaffected by the dielectric environment and shows a turnover between two power laws. We relate this turnover to an intermediate step during the ionization of the QDs involving surface states.