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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Poster: Nanoparticles and Composite Materials

CPP 36.23: Poster

Mittwoch, 24. März 2010, 17:30–19:00, Poster B2

Optical Detection of Charged Quantum Dots in Solution — •Nicole Amecke-Mönnighoff and Frank Cichos — Molecular Nanophotonics Group, University of Leipzig, Linnéstraße 5, 04103 Leipzig

The fluorescence properties of semiconductor Quantum Dots (QDs) are intensively studied due to many potential applications, which want to make use of their tunable emission wavelength, high quantum yield and photon statistics. Additionally some peculiarities like power-law blinking, lifetime-fluctuations and spectral diffusion can be found. Most of those can be explained by charges close to or in the dot center leading to Auger processes and the quantum confined stark effect. Charges can arise from ejection of electron or hole via tunneling leaving behind the counterpart. One of the main ideas is, thus, the development of an experimental method and setup for controlling and investigating those charges on the single particle level, while monitoring the particles' flourescence. We thus combine confocal microscopy with a setup of two electrodes in solution. When applying a voltage, we can measure the intensity and lifetime changes of the particles in different distances close to the electrode. What we surprisingly find is electrophoresis of a great part of QDs possessing a net positive charge, even though being dispersed in the non-polar solvent toluene. Furthermore they were still fluorescent and no measurable change in lifetime was detected, which is very interesting to the basic understanding of charges quenching a QDs fluorescence. Our goals now are determining this charge's origin, amount and precise location, including also that of the counter charge.