This thesis reports the photophysical and electroluminescence studies undertaken on two types of material: polymeric and dendritic. The dendritic architecture is a recent concept adopted to develop new materials for light-emitting diodes. The dendritic structure offers a combination of properties of both polymers and small organic molecules whilst having their own interesting characteristic of optimising processibility, charge transport, and optical properties independently. The dendritic structure consists of functional surface groups, conjugated dendrons and a conjugated core. Initial optical (absorption and photoluminescence) studies revealed that the dendrimer emission originates from the core and is independent of excitation wavelength. This was investigated further in distyrylbenzene based dendrimers where the effect of dendrimer generation number on photoluminescence and electroluminescence properties was studied. All dendrimers emit blue electroluminescence with, in some cases, reasonable electroluminescence quantum efficiency in the range of 0.09 % and brightness up to 150 Cd m(^-2). Having established that the furmel effect, where excitation is successfully transferred to the dendrimer core in both PL and EL, different chromophores were incorporated in the dendrimer structure. Colour control was thus demonstrated in EL devices of the different dendrimers, showing the possibility of using a large number of chromophores in a processible form for EL applications. Conjugated polymers were also studied to investigate the nature of the emitting species (poly(p-pyridine)) and the effect of side- chains (poly(p-phenylenevinylene)). In poly(p-pyridine) the emission was found to be strongly dependent on pyridyl ring rotation affecting the emission and its quantum yield while the side-chains in the poly(p-phenylenevinylene) derivatives were found to affect polymer properties such as degree of conversion of non-conjugated to conjugated polymer. The PL quantum yield system was set-up and proved useful in assessing synthesis of new materials.

Thesis (Ph.D.)--McMaster University, 2003. / Advisor: A.H. Kitai. Includes bibliographical references (leaves 193-199). Also available via World Wide Web.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

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Single self-assembled semiconductor quantum dots (QDs) are able to emit single-photons and entangled-photons pairs. They are therefore considered as potential candidate building blocks for quantum information processing (QIP) and communication. To exploit them fully, the ability to precisely control their optical properties is needed due to several reasons. For example, the stochastic nature of their growth ends up with only little probability of finding any two or more QDs emitting indistinguishable photons. These are required for two-photon quantum interference (partial Bell-state measurement), which lies at the heart of linear optics QIP. Also, most of the as-grown QDs do not fulfil the symmetries required for generation of entangled-photon pairs. Additionally, tuning is required to establish completely new systems, for example, 87Rb atomic-vapors based hybrid semiconductoratomic (HSA) interface or QDs with significant heavy-hole (HH)-light-hole (LH) mixings. The former paves a way towards quantum memories and the latter makes the optical control of hole spins much easier required for spin- based QIP. This work focuses on the optical properties of a new type of QDs optimized for HSA experiments and their broadband tuning using strain. It was created by integrating the membranes, containing QDs, onto relaxor-ferroelectric actuators and was quantified with a spatial resolution of ~1 µm by combining measurements of the µ-photoluminescence of the regions surrounding the QDs and dedicated modeling. The emission of a neutral exciton confined in a QD usually consists of two fine-structure-split lines which are linearly polarized along orthogonal directions. In our QDs we tune the emission energies as large as ~23meV and the fine-structure-splitting by more than 90 µeV. For the first time, we demonstrate that strain is able to tune the angle between the polarization direction of these two lines up to 40° due to increased strain-induced HH-LH mixings up to ~55%. Compared to other quantum emitters, QDs can be easily integrated into optoelectronic devices, which enable, for example, the generation of non-classical light under electrical injection. A novel method to create sub-micrometer sized current-channels to efficiently feed charge carriers into single QDs is presented in this thesis. It is based on focused-laserbeam assisted thermal diffusion of manganese interstitial ions from the top GaMnAs layer into the underlying layer of resonant tunneling diode structures. The combination of the two methods investigated in this thesis may lead to new QDbased devices, where direct laser writing is employed to preselect QDs by creating localized current-channels and strain is used to fine tune their optical properties to match the demanding requirements imposed by QIP concepts.