Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 9: POSTERS Single Molecules, Biopolymers, Membranes

CPP 9.6: Poster

Montag, 25. Februar 2008, 16:45–19:00, Poster A

Investigations of single quantum dot (QD) blinking via Fluorescence Correlation Spectroscopy (FCS) — •Nicole Amecke and Frank Cichos — Molecular Nanophotonics Group, University of Leipzig, Linnéstraße 5, 04103 Leipzig

The intermittency of QD fluorescence (blinking) is a well known, intensively studied, but still not fully understood phenomenon. Control over this peculiarity is strongly desired for many applications of QDs as reliable light sources. This however remains still a fair wish and needs deeper understanding of the underlying processes. The observed dark states are supposed to result from ionization processes, where one charge is ejected from the QD into localized states of the surrounding medium. Auger processes, enabled by the remaining charge, will then inhibit photon emission until neutralization. The durations of dark (charged) as well as bright (neutral) periods are found to obey power law statistics, which can be understood to result from a tunneling process of the charge to and from a wide distribution of trap states in the matrix. This explanation holds for a solid matrix while deviations in liquid matrices can be expected. In ensemble investigations effects of blinking simply result in lower emission intensity. FCS, however, offers a method to investigate blinking of QDs in solution. When keeping the detection volume small via confocal spectroscopy, the diffusion of single emitters through the focus can be investigated, obtaining diffusion properties, but also blinking effects. We find that both, shape and contrast, of the correlation function depend on the excitation power. This leads to an apparent concentration change as deduced by FCS.