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    Picosecond Energy Transfer in Quantum Dot Langmuir-Blodgett Nanoassemblies

    Year: 2003

    Journal: J. Phys. Chem. B 2003, 107, 13782-13787, 20111221

    Authors: Marc Achermann, Melissa A. Petruska, Scott A. Crooker, and Victor I. Klimov

    Organizations: Chemistry Division, C-PCS, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 and National High Magnetic Field Laboratory, MST-NHMFL, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

    We study spectrally resolved dynamics of Förster energy transfer in single monolayers and bilayers of semiconductor nanocrystal quantum dots assembled using Langmuir-Blodgett (LB) techniques. For a single monolayer, we observe a distribution of transfer times from ~50 ps to ~10 ns, which can be quantitatively modeled assuming that the energy transfer is dominated by interactions of a donor nanocrystal with acceptor nanocrystals from the first three "shells" surrounding the donor. We also detect an effective enhancement of the absorption cross section (up to a factor of 4) for larger nanocrystals on the "red" side of the size distribution, which results from strong, interdot electrostatic coupling in the LB film (the light-harvesting antenna effect). By assembling bilayers of nanocrystals of two different sizes, we are able to improve the donor-acceptor spectral overlap for engineered transfer in a specific ("vertical") direction. These bilayers show a fast, unidirectional energy flow with a time constant of ~120 ps.