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Energy Transfer via Exciton Transport in Quantum Dot Based Self-Assembled Fractal Structures

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journal contribution
posted on 06.03.2014 by César Bernardo, I. Moura, Y. Núnez Fernández, Eduardo J. Nunes-Pereira, Paulo J. G. Coutinho, Arlindo M. Fontes Garcia, Peter Schellenberg, Michael Belsley, Manuel F. Costa, Tobias Stauber, Mikhail I. Vasilevskiy
Semiconductor quantum dot (QD) assemblies are promising systems for light harvesting and energy conversion and transfer, as they have a superior photostability compared to classical dyes and their absorption and emission properties can be tuned during synthesis. Here, we investigate excitonic energy transfer in self-assembled dentrite-type fractal structures consisting of QDs by microscopically mapping their fluorescence spectra and lifetimes. The behaviors of CdSe/ZnS and CdTe QD assemblies are compared; in particular, the energy transfer probability is found to be stronger in CdTe-based structures, scaling with their radiation quantum yield. Our results indicate Förster-type energy transfer in both systems, although with a higher efficiency in CdTe. The energy transfer is caused by near-field (nonradiative) dipole–dipole coupling between the individual QDs within a dendrite, with the excitation migrating from the edges to the center of the structure. The experimental findings are supported by theoretical modeling results obtained by using master equations for exciton migration/decay kinetics in diffusion-limited fractal aggregates composed of identical particles.