Dresden 2011 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Poster: Nanoparticles and Composite Materials

CPP 36.15: Poster

Wednesday, March 16, 2011, 17:00–19:00, P2

Detection of a surface charge on fluorescent CdSe/ZnS Quantum Dots in Toluene — •Nicole Amecke and Frank Cichos — Molecular Nanophotonics, University of Leipzig, Leipzig, Germany

Semiconductor nanocrystals, that fluoresce in the visible range like CdSe/ZnS QDs, have been a widely studied material over the last decades due to applications in bio-labeling, laser diodes, solar cells and many others. Their size-tunable fluorescence shows high quantum yields, however most synthesized single crystals still show fluctuating and interrupted emission. Those effects have been mostly assumed to be due to charges in the crystal core or at the surface leading to non-radiative decay channels and spectral shifts. However, those charges remain difficult to investigate during fluorescence detection. We took another step to change this, using a confocal microscope and investigating the fluorescence intensity of QDs in a homogeneous electric field close to one electrode. We find motion to the negative electrode and the formation of a screening layer. Despite the positive charge on these particles we measure a fluorescence lifetime comparable to that of immobilized single particles. Thus, a charge in the core can be excluded. As we are measuring in toluene, an intrinsic surface charge is suggested. We estimate the amount of this charge and the percentage of charged particles by comparing velocities and concentrations with simple electrophoretic dynamics. The possibility for this charge as origin of the measured intensity fluctuations of immobilized particles is discussed.