Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: Nanoparticles and Composite Materials

CPP 2.10: Talk

Monday, March 26, 2012, 12:15–12:30, C 243

Cross-over in the power law statistics of the fluorescence of CdSe/CdS/ZnS nanocrystals — •Gerald Hinze and Thomas Basché — Institut für Physikalische Chemie, Johannes Gutenberg-Universität, 55099 Mainz

Semiconducting quantum dots (QD) are often characterized by bright luminescence and high photo stability compared to usual aromatic molecular dyes. On a single particle level, however, their fluorescence typically shows intermittencies. That is, under continuous light illumination stochastic jumps between light (on) and dark states (off) occur. At the same time the fluorescence decay from single QDs often cannot described by a single exponential. Recently, there have been attempts to explain both observations within a single model implementing an additional dark state. We have studied CdSe/CdS/ZnS colloidal quantum dot emission over 9 decades in time. By combining different experimental setups we were able to follow the temporal evolution of the fluorescence intensity of a bulk sample from ns to seconds. We observe three inverse power-laws differing in the exponent with cross over times at ∼100µs and ∼5ms. From single molecule intensity time traces we calculated the off-time statistics related to the intermittency of the fluorescence. Within the accessible range of the off-time statistics, which was obtained for 3 decades of time, it nicely matches the time-dependent fluorescence intensity. Our results support the recent proposed model of diffusion-controlled electron transfer being the origin for the observed power law statistics.