Selective plasmonic control of excitons and their non-radiative energy transfer in colloidal semiconductor quantum dot solids
Author
Özel, Tuncay
Advisor
Demir, Hilmi Volkan
Date
2009Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
To date extensive research has proved that semiconductors and metals exhibit
extraordinary optical properties in nano-dimensions compared to their bulk
counterparts. For example, an interesting effect is observed in metal
nanostructures/nanoparticles (NPs) that we form to obtain localized plasmons,
with their optical response highly tuneable using the size effect. Another field of
interest at the nanoscale is the investigation of light generation and harvesting
using colloidal semiconductor quantum dot nanocrystals (NCs) that we
synthesize in few nanometers, with their emission and absorption excitonic
peaks conveniently tuneable using the size effect. In this thesis, we proposed and
demonstrated the first accounts of selectively plasmonically-controlled colloidal
quantum dot emitters assembled in innovative architectures, with a control
achieved either through spatial selection or spectral selection. In the first set of
designs, we developed for the first time plasmonic NC-composites that rely on
spatially-selected plasmon-coupled CdTe NC-monolayers interspaced with
respect to Au NP-monolayers in a repeating three-dimensional layer-by-layer
architecture. In these bottom-up designs of hybrid nanocomposites, the
photoluminescence kinetics is strongly modified and a record quantum
efficiency of 30% is achieved for such CdTe NC solids. In the second set of designs, we showed the first spectrally-selected plasmon-coupling of surfaceemitting
CdS NCs using optimized Ag NP deposits. This architecture allowed
for the surface-state emission to be selectively enhanced while the interband
emission is simultaneously suppressed in the same plasmon-coupled NCs,
leading to the strongest surface-state emission from such CdS NCs reported with
respect to their interband emission (with a >12-fold enhancement). Yet another
important proximity phenomenon effective among quantum dot emitters is the
Förster-type non-radiative resonance energy transfer (ET), in which excitonic
excitation energy of the donor-NCs is non-radiatively transferred to the
acceptor-NCs via dipole-dipole coupling. In the third set of our designs, we
combined two fundamental proximity mechanisms of plasmon coupling and
non-radiative energy transfer in the same NC solids. In plasmonic ET, we
reported for the first time selectively plasmon-coupling of NC-acceptors and
then that of NC-donors in the ET pair, both of which result in substantial
enhancement of the acceptor emission with respect to ET with no plasmon
coupling (with a maximum of 2-fold enhancement) as verified by their steadystate
and time-resolved photoluminescence. This concept of spectrally/spatiallyselective
plasmon coupling in quantum dots paves a new path for devices and
sensors in nanophotonics.
Keywords
Plasmonicslocalized plasmons
metal nanoparticles
metal nanostructures
non-radiative Förster energy transfer
semiconductor nanocrystals
colloidal quantum dots
excitons
spontaneous emission
photoluminescence
metal-enhanced luminescence
FDTD