Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Dennis G. Deppe. Vita. Includes bibliographical references.

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

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / William Doolittle, Committee Member ; Joy Laskar, Committee Member ; Russell Dupuis, Committee Chair ; David Citrin, Committee Member ; Srinivas Garimella, Committee Member.

Made available in DSpace on 2014-10-09T12:28:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:06Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP; Faculdade de Odontologia, Universidade de Sao Paulo, Sao Paulo

Developing organic light-emitting diodes (OLEDs) as the next generation display devices is not only of industrial interest, but also a scientific challenge in and of itself that requires multi-disciplinary efforts to make the technology successful. Thermally activated delayed fluorescence (TADF) is a recent breakthrough in OLED technology whose prime value is to enable purely organic emitters to recruit the dark triplet excitons in the device, thus avoiding expensive and toxic rare metal based emitters. This thesis is centred on TADF and contains work in three major areas. Firstly, novel ionic TADF emitters were designed for use in light-emitting electrochemical cells (LEECs), which is an alternative electroluminescent device technology to OLEDs, with a much simplified fabrication procedure and architecture. The vast majority of these ionic emitters are based on reported TADF scaffolds where the donors were tethered with an imidazolium hexafluorophosphate group to obtain the ionic character required for LEEC devices (TL and BTL series, Chapter 2). On the other hand, TADF emitters with a carboxylate group were also designed which act as both acceptor and intrinsic charged functionality for LEEC applications (CTL series, Chapter 2). Secondly, attempts were made to create novel TADF molecular scaffolds in order to enrich the current library of TADF emitters. Research efforts were focused on polyaromatic moieties such as anthracene (An series, Chapter 4) and fluoranthene (FA series, Chapter 4) that are seldom reported in TADF literature. In addition, TADF emitters with phosphine oxide as the acceptor group have also been studied (PO series, Chapter 5). Lastly, structure-property relationship studies of TADF emitters were undertaken as a function of tuning of donor and acceptor functionalities using both theoretical and experimental approaches in order to gain more insight for designing desirable TADF emitters (Chapter 3).

Efficient and high light amplification of optical resonator in organic laser is one of the critical factors for high performance organic laser. It can be achieved by using microcavity and DFB structures, which are commonly adopted methods to enhance light amplification in specific wavelength. Both of them are the more widely used structures in inorganic and organic lasers. In this work, we employed nearly 100% reflection (at 450 nm) DBR and Al to act as reflected mirror inside the microcavity device. The function of microcavity has been examined to show the ability of device in tuning laser emission wavelength and overcoming the loss of organic-metal interface. DFB structure was used to demonstrate different laser emissions with respect to different grating periods. The finding clarifies the role of the structure in enhancement of light amplification leading to lower threshold, which was half of that of amplified spontaneous emission from single layer of PFO. As designed laser mode is also an important factor to get a high performance organic laser, those laser modes of structures have been designed and estimated by simulations and consistent with the experimental results. Color tunable light source has great potential for display, lighting and bio-imaging. Current broadband light sources, however, have their own limitations in beam divergence and device size. In this work, we demonstrated a spatially variant light source with tunable color emission property by using two cascaded organic thin films, which emit blue and green ASE respectively under optical pumping. By spatially selecting the overlapping of the directional ASE from the cascaded films, we show that the color of light emission can be continuously tuned from blue, white to green.

The plasmonic properties of silver-based alloy thin films were studied. Silver-ytterbium (Ag-Yb) and silver-magnesium (Ag-Mg) prepared by thermal co-evaporation were investigated extensively for various thin film properties. The optical properties were intensively analyzed and discussed because the dielectric response of a material is particularly significant in terms of its plasmonic properties. The study of silver-based alloy thin films has been mostly about Ag alloying with other transition metals, but the results of Ag-Yb and Ag-Mg in this work showed that the intensity of plasma resonance is tunable, in which the idea may also apply to other silver-rich binary alloy thin films regardless of the kind of second metal components. In our research, the Ag plasma resonance was weakened with respect to the concentration of Yb and Mg in the alloy thin films. The change in the optical characteristics around Ag plasma resonance frequency was attributed to an increase in “resonance damping. This is confirmed from modeling using classical free-electron theory. The increase in the damping was experimentally corroborated by the concentration dependence of electrical conductivity and estimated average crystallite size of Ag-Yb and Ag-Mg thin films. The reduction in electrical conductivity was not only caused by introducing less conductive Yb or Mg but also through disturbing the Ag lattice structure to promote additional electron scattering at grain boundaries. The Ag-Yb and Ag-Mg alloys carried intermediate properties between their pure components despite the presence of Yb or Mg oxides. Besides optical and electrical properties, changes in the electronic work function were also assessed since it is also important in applications. Plasmonic nanostructures and transparent organic light-emitting diodes (OLEDs) were fabricated to demonstrate their potential applications. Two-dimensional disc-arrays nanostructures composed of pure Ag and Ag-Yb were implemented to evaluate the plasmonic properties. The damping loss in Ag-Yb caused weakened coupling of incident photons and surface plasmons when compared to pure Ag without altering the coupling wavelengths, suggesting potential plasmonic materials for tuning the coupling strength of surface plasmons by controlling the concentration of Yb which may also apply to Ag-Mg. Ultrathin Ag-Yb and Ag-Mg films were used as cathodes in transparent OLEDs for demonstration, which was beneficial by virtue of overall device transmittance though sacrificing electrical conduction leading to poor light emission unless inserting additional ultrathin lithium fluoride to modify the ultrathin cathodes.

Made available in DSpace on 2014-10-09T12:33:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:22Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP; Faculdade de Odontologia, Universidade de Sao Paulo, Sao Paulo

Made available in DSpace on 2014-10-09T12:28:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:06Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP; Faculdade de Odontologia, Universidade de Sao Paulo, Sao Paulo