Exciton harvesting systems of nanocrystals
Author
Mutlugün, Evren
Advisor
Demir, Hilmi Volkan
Date
2011Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Semiconductor nanocrystals, also known as colloidal quantum dots, have gained
substantial scientific interest for innovative light harvesting applications
including those in biolabeling. Organic dyes and fluorescent proteins are widely
used in biotargeting and live cell imaging, but their intrinsic optical properties,
such as narrow excitation windows, limit their potential for advanced
applications, e.g., spectral multiplexing. Compared to these organic
fluorophores, favorable properties of the quantum dots including high
photoluminescence quantum yields together with tunable emission peaks and
narrow spectral emission widths, high extinction coefficients, and broad
absorption bands enable us to discover and innovate light harvesting composites.
In such systems, however, the scientific challenge is to achieve high levels of
energy transfer from one species to the other, with additional features of
versatility and tunability.
To address these problems, as a conceptual advancement, this thesis proposes
and demonstrates a new class of versatile light harvesting systems of
semiconductor nanocrystals mediated by excitonic interactions based on Förstertype
nonradiative energy transfer. In this thesis, we synthesized near-unity
efficiency colloidal quantum dots with as-synthesized photoluminescence
quantum yields of >95%. As proof-of-concept demonstrations, we studied and
achieved highly efficient exciton harvesting systems of quantum dots bound to
fluorescent proteins, where the excitons are zipped from the dots to the proteins
in the composite. This led to many folds of light harvesting (tunable up to 15 times) in the case of the green fluorescent protein. Using organic dye molecules
electrostatically interacting with quantum dots, we showed high levels of
exciton migration from the dots to the molecules (up to 94%). Furthermore, we
demonstrated stand-alone, flexible membranes of nanocrystals in
unprecedentedly large areas (> 50 cm × 50 cm), which paves the way for highend,
large-scale applications. In the thesis, we also developed exciton-exciton
coupling models to support the experimental results. This thesis opens up new
possibilities for exciton-harvesting in biolabeling and optoelectronics.