Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Nanoparticles and Composite Materials II

CPP 41.6: Talk

Thursday, March 25, 2010, 15:15–15:30, H48

Net Charge on Colloidal CdSe/ZnS Evidots in Nonpolar Solvents — •Nicole Amecke-Mönnighoff and Frank Cichos — Molecular Nanophotonics Group, University of Leipzig, Linnéstraße 5,04103 Leipzig

An interesting and promising class of materials studied over the last years are semiconductor Quantum Dots (QDs). Many applications seek to make use of their favorable fluorescence characteristics, like tunable emission wavelength, high quantum yield and antibunching. Additionally they show certain peculiarities like power-law blinking, lifetime-fluctuations and spectral diffusion which can be explained by charges close to or in the dot center leading to Auger processes and the quantum confined Stark effect. Those charges can arise from ejection of electron or hole via tunneling leaving behind the counterpart and changing the matrix charge constellation. So far the model, assuming the net charge of a QD plus close surroundings to be zero. When applying an electric field to a solution of QDs in toluene, we surprisingly find a net positive charge on a great part of QDs, even though being dispersed in a nonpolar solvent. As those charged QDs still fluoresce the charge will most likely be located at the surface. Since this surface charge is very unlikely to be formed in the nonpolar toluene, we suggest that it is the result of the synthesis of the QDs. Such a charge should definitely influence blinking and probably all the characteristics mentioned above. It even might bias electron tunneling and should thus be included in blinking models. Our first goal is to find its origin, amount and precise location, including also that of the counter charge.