Cascading and modifying nonradiative energy transfer mechanisms in strong coupling region of plasmons and excitons in semiconductor quantum dots

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Author
Akın, Onur
Advisor
Demir, Hilmi Volkan
Date
2010Publisher
Bilkent University
Language
English
Type
Thesis
Metadata
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http://hdl.handle.net/11693/15471Abstract
Nonradiative energy transfer finds important applications in nanophotonics and
nanobiotechnology including nanoscale optical waveguiding and biological
nanosensors. Various fluorophores can take part in such energy transfer
interactions in close proximity of each other. Their emission kinetics can be
strongly modified and controlled as a result. For example, colloidal
semiconductor quantum dots, also known as nanocrystals, have widely been
shown to serve as donors and acceptors among themselves or with other
fluorescent species to transfer excitation energy nonradiatively. In their close
proximity, emission characteristics of such fluorophores can also be altered
when coupled with plasmonic structures, e.g., metal nanoparticles. One favored
result of these plasmon-exciton interactions is the emission enhancement. In
principle it is possible to plasmon-couple acceptor-donor pairs of nonradiative
energy transfer to modify their transfer rate. Such plasmon-mediated energy
transfer has been demonstrated, where both acceptor-donor pairs are plasmoncoupled.
In these cases, however, the resulting plasmon-exciton interactions are
not controlled to take place either at the donor site or the acceptor site but at
both of the sites. Therefore, it has previously not been possible to identify the
coupled interactions. In this thesis, we propose and demonstrate cascaded
plasmonic - nonradiative energy transfer interactions that are controlled by
selectively plasmon-coupling either only the donor quantum dots or only the
acceptor quantum dots. For that, we designed a novel self-assembly architecture
of our hybrid layered systems of semiconductor nanocrystals and metal
nanoparticles in a bottom-up fashion through precise spatial and spectral control.
This scheme uniquely allowed for the ability to spatially control plasmonexciton
interactions to take place either at the “start” site (donors) or “finish”
site (acceptors) of the energy transfer. This control was achieved by placing the
plasmonic layer in the right proximity of the donors (for strong donor-exciton
plasmon-coupling) while sufficiently being far away from the acceptors (for
weak acceptor-exciton plasmon-coupling), or vice versa. Here we comparatively
studied and analyzed consequent modifications of quantum dot emission
kinetics in response to both cases of plasmon-coupling to only the donors and to
only the acceptors through steady-state and time-resolved photoluminescence
measurements, along with their lifetime and rate calculations. Such cascaded
energy transfer interactions in the strong exciton-plasmon coupling region hold
great promise for innovative near-field photonic devices and biological tags.
system.