Thesis (Ph. D.)--University of Washington, 2006. / Includes bibliographical references (leaves 157-161).

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xii, 96 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 56-59).

In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications. The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defects–an important material parameterand“measure”of the structure optical quality–is found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons. In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces. Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.

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published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

This thesis describes the synthesis of polyyne rotaxanes and an investigation of their excited state photophysical properties. The threading of dumbbell-shaped carbon chains with macrocyclic components is a way to mechanically insulate and control the environment around the carbon chains. The resulting polyyne rotaxanes can serve as model compounds for insulated carbyne. Different strategies have been tested for the synthesis of polyyne rotaxanes with different topologies and structures. Study of rotaxanes in the excited states reveals strong electronic communication between an acetylenic thread and a macrocycle. Chapter 1 summarizes the field of acetylene scaffolding, introducing some recent achievements in acetylene chemistry. General synthetic methods for polyynes are discussed, and an introduction to active metal template synthesis of rotaxanes is given. Chapter 2 describes the synthesis of a family of polyyne rotaxanes with different axle lengths and macrocycles, prepared by homocoupling of terminal alkynes. Synthesis of hexayne rotaxane with functional pyridine end-group is presented and a number of crystal structures of polyyne rotaxanes are analyzed. Chapter 3 demonstrates the use of acetylene cross-coupling in the synthesis of rotaxanes. Synthesis of rotaxanes with different topological structure is provided. Chapter 4 details the excited state properties of polyynes studied by time -resolved spectroscopy. The complexes of rhenium(I) carbonyls with rotaxanes is presented and the excited state energy transfer in rotaxanes is studied. Chapter 5 explores new synthetic strategies for polyyne rotaxanes, using "masked" precursors. It also highlights the potential of carbenoid rearrangement of alkyliden es for the construction of linear and cyclic architectures. Chapter 6 is the summary of the project and general discussion of future directions. There are two appendices in the end of thesis: Appendix A covers the photophysics of rhenium tricarbonyl complex of the hexayne rotaxane with a small macrocycle and Appendix B reports work towards the synthesis of rotaxanes with platinum(II)-alkyne complexes.

Time-resolved photoluminescence (TRPL) measurements paired with steady-state photoluminescence (SSPL) measurements can help to determine the PL lifetime, shape and position of unresolved bands, capture coefficients, and concentrations of free electrons and defects.PL bands that are obscured in the SSPL spectra can be accurately revealed by TRPL measurements. TRPL measurements are able to show if the PL band originates from an internal transition between different states of the same defect. The main defect-related PL bands in high-purity GaN grown by hydride vapor phase epitaxy (HVPE) which have been investigated are the ultraviolet, blue, green, yellow and red luminescence bands (UVL, BL, GL, YL and RL, respectively). The concentration of free electrons can be calculated from these measurements providing a contactless alternative to the Hall effect method. The lifetime of most defect-related PL bands decreases with increasing temperature. However, the lifetime of the GL band, with a maximum at 2.4 eV observed in the SSPL spectra only at high excitation intensity, increases as a function of temperature. By analyzing the PL intensity decay, the origin of the GL can be attributed to an internal transition from an excited state of the CN defect, which behaves as an optically generated giant trap, to the 0/+ level of the same defect. This first observation of an optically generated giant trap was detected by analyzing the cubic temperature dependence of the electron capture coefficient. Excitation intensity and temperature dependent studies on Mg-doped GaN grown by HVPE were performed. The position of the UVL (3.2 eV) peak blue-shifts with increasing excitation intensity, which can be explained by the presence of potential fluctuations. The BL peak (2.8 eV) also blue-shifts with increasing excitation intensity, and red-shifts as a function of temperature. These shifts can be explained by the transitions originating from a deep-donor to the MgGa acceptor, and the corresponding donor-acceptor pair nature.

Understanding and identifying critical protein-protein interactions is just one of the key outcomes in biological research. It can help to confirm key cellular interactions, which in some fields, such as cancer research, can result in a greater understanding of disease pathogenesis, elucidate mechanisms of therapeutic resistance and aid in the development of new specific targets, leading to new methods of prevention and treatment. Time-correlated single photon counting fluorescence lifetime imaging microscopy is just one of the tools used to carry out this line of research. Here we demonstrate a direct interaction between two proteins involved in gene regulation and expression; p21 and FMN2. Furthermore, we also show the capability of this system to measure chromatin compaction in three dimensions. However, fluorescence lifetime imaging has some drawbacks, acquisition times on such a system can range from the tens of seconds to minutes, which is often too long to comprehensively measure many biological events. But microscopy is always developing, aided by new techniques and, perhaps even more so, new technological developments. This thesis also demonstrates two new methods of light sheet microscopy, that use both new equipment made available because of technological developments to allow time resolved imaging and traditional microscopic aspects to form a light sheet system based on polarisation. It outlines the design and how to build these systems and presents their function to show their great promise. Both techniques presented in this thesis utilise aspects of light not conventionally used in light sheet microscopy. Further development of these systems and application of emerging technologies will yield a system capable of outperforming current light sheet fluorescence microscopy-based fluorescence lifetime imaging techniques. The implementation of polarisation control into such a system would enable three-dimensional anisotropy based SPIM-FLIM measurements, an indispensable tool in researching molecular orientation and mobility at a macroscopic level in developing organisms.