While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs.

Transparent conductive oxides are an essential part of technologies that require both large-area electrical contact and optical access in the visible portion of the light spectrum. SnO2 doped with Fluorine (SnO2: F) and In2O3 doped with tin (ITO) are the most popular choices of front contacts for CdTe solar cells. In this thesis, CdS/CdTe devices were fabricated with SnO2: F (MOCVD) and ITO (sputtering) as front contacts without a high resistivity (resistivity relatively greater than front contact) buffer layer. The device characteristics of these devices were low but improved considerably after the inclusion of an intrinsic SnO2 (SnO2-i) deposited by MOCVD as buffer. Thus having emphasized and demonstrated the benefits of a buffer layer in these devices, the use of reactively sputtered SnO2 (intrinsic), SnO2 doped with Zinc (5% and 10% Zinc) and In2O3(intrinsic) as buffer layers in SnO2:F/buffer/CdS/CdTe devices were explored. Experiments were also carried out on the photovoltaic active layers of SnO2:F/SnO2-i/CdS/CdTe Solar cells. Namely, the effect of window layer thickness was studied by making a series of devices in which the CdS thickness was progressively reduced and the effect of substrate temperature (Tsub) during the deposition of the absorber layer was also studied by increasing Tsub > 600°C during CdTe CSS. In order to determine the effectiveness of In2O3 as a buffer layer, a series of ITO/In2O3/CdS/CdTe cells were fabricated with varying thickness of In2O3 (250 to 2000 Ǻ) and also the CdS thickness was reduced in steps (~800 Ǻ to~500 Ǻ) in these devices. ITO/ In2O3 device with efficiency greater than 14% (Voc: 820 mV, FF: 72% and Jsc: 24 mA/cm2 ) was fabricated for an In2O3 thickness of 250 Ǻ and CdS thickness of ~ 600 Ǻ. However the best efficiency of 14.7% (Voc: 830 mV, FF: 77%, Jsc: 23 mA/cm2 ) was achieved for SnO2:F/SnO2-i/CdS/CdTe device. ITO films with resistivity as low as 1.9X10-4 Ω-cm, mobility 32 cm2V-1s-1 and average transmission ~ 90% in the visible region were obtained for carrier concentration in the order of 1.1X1021 cm-3.

Includes bibliographical references. Details research carried out into the nonlinear optical properties of metal alkynyls, chiefly organoruthenium complexes, showing that these complexes can be designed to have very large NLO coefficients. Also demonstrates the utility of spectroscopic, electrochemical and copmutational aids as predictive tools for NLO materials. Also examines cluster synthesis, reactivity and physical properties using ruthenium clusters and hard-donor ligands, affording a series of cluster complrxes that provide structural models for industrially-important hydrotreating intermediates.

Includes bibliographical references. / 3 v. : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Details research carried out into the nonlinear optical properties of metal alkynyls, chiefly organoruthenium complexes, showing that these complexes can be designed to have very large NLO coefficients. Also demonstrates the utility of spectroscopic, electrochemical and copmutational aids as predictive tools for NLO materials. Also examines cluster synthesis, reactivity and physical properties using ruthenium clusters and hard-donor ligands, affording a series of cluster complrxes that provide structural models for industrially-important hydrotreating intermediates. / Thesis (D.Sc.)--University of Adelaide, Dept. of Chemistry, 2003

<p>The Large Hadron Collider (LHC) at CERN have a capacity to produce protonproton collisions with an energy of 14 TeV. Four particle detectors are included in the LHC with the purpose to detect all the particles that are created in the collisions. In one of these detectors are scintillating lead tungstate crystals used, to detect the energy of photons and electrons created in the collisions. The energy is detected by measuring of the emitted light from the scintillating crystals. As much knowledge as possible about the optical properties of the crystals are desired to be able to analyze the acquired data from the crystals.</p><p><p>This thesis work presents some techniques used for the characterization of the optical properties for the crystals. It also presents measurements done on the decay time of lead tungstate crystals and on the temperature influence to the light yield from the crystals. These measurement results are in addition used in an attempt to estimate how big influence the Cherenkov radiation has to the total amount of emitted light from the scintillating crystals.</p><p>The influence from the temperature to the light yield is around <em>−</em>2<em>.</em>02 %<em>/◦C </em>for BTCP and around <em>−</em>1<em>.</em>75 %<em>/◦C </em>for SIC¹. No conclusions could been drawn concerning the influence from the Cherenkov radiation to the total amount of emitted light from the temperature measurements.The decay time measurements showed an influence from the Cherenkov radiation to the total amount of emitted light of; 8 % for crystal 1003, 47 % for crystal 1002 and 19 % for crystal 1001.</p></p><p><p><p>¹BTCP (Bogoroditsk Technical Chemical Plant) and SIC (Shanghai Institute of Ceramics) are the two different crystal production facilities used for the production of the crystals.</p></p></p>

New transparent p- and n-type semiconductors and luminescent materials have been prepared and characterized. Synthesis, structures, optical and electrical properties of new chalcogenide fluoride p-type transparent semiconductors MCuQF (M=Ba, Sr; Q=S, Se, Te) are described. Band-gap tuning and improvement in conductivity through p-type doping are demonstrated in the family. The new Ag sulfide fluoride BaAgSF has been prepared, and its optical and electrical properties have been examined. Phase stabilization as well as optical and electrical properties of the p-type conductors BaCu₂S₂ and BaCu₂Se₂ are considered. New n-type transparent conducting films of W-doped In₂O₃ and W-doped zinc indium oxide (ZIO) have been prepared by pulsed laser deposition, and their electrical properties have been examined. Results on new transparent thin-film transistors containing SnO₂ or ZIO are also presented. Strong near-infrared luminescence of BaSnO3 is described, and the emission brightness is correlated to the crystallite size of assembled nanoparticles. Syntheses, structures, and optical properties of (La,Y)Sc₃(BO₃)₄:Eu³⁺, (Ba,Sr)Sc₂(BO₃)₄:Eu²⁺, and LuAl₃(BO₃)₄:Ln³⁺ (Ln=Eu, Tb, Ce) have been considered with emphasis on relations between structures and optical properties. Finally, the synthesis and luminescence properties of new potential X-ray phosphors Lu₂O₂S:Ln³⁺ (Ln=Eu, Tb) are summarized. / Graduation date: 2005

Graduation date: 2005

Holographic techniques were used to study the optical properties and bistable behavior of Ga-doped cadmium fluoride. Ga impurities form bistable centers in CdF���. Illumination causes a phototransformation from a deep to shallow center, which causes a change in the index of refraction. This change is caused by a redistribution of electrons in the centers, and is known as the photorefractive effect. The photorefractive effect makes it possible to write holographic patterns into the material. Using intersecting laser beams, a holographic grating was written into the sample, and the behavior of this grating was studied. The decay and efficiency of the grating are temperature dependent. The thermal decay that is responsible for erasing the grating is a two-center process. The thermal activation energy between the centers is about 780 meV. / Graduation date: 2000

The behavior and application of organic semiconductor materials depend strongly on their molecular structure, and molecular interactions. Several studies of intermolecular interactions in functionalized polyacene materials are presented. The degree and onset of aggregation of a functionalized anthradithiophene derivative was studied as a function of concentration in two different host matrices. The molecular environment was found to influence the degree and onset, but not the nature of aggregate formed. The effect of aggregation on photoconductivity was also studied. In a blend of two different anthradithiophene derivatives, the intermolecular separation was found to affect the nature of the interaction, transitioning from energy transfer at large intermolecular distances to the formation of an emissive excited state complex at smaller intermolecular distances. This complex was shown to have effects on both photoluminescence and photoconductivity. Finally, a single molecule fluorescence microscopy system was built and characterized. Software was written to process data produced from the system and several classes of functionalized polyacenes were studied at the single molecule level. In particular, the photophysics and molecular orientation of various derivatives were quantified. A new solution-processable, photoconductive, polycrystalline host material was found to be suitable for single molecule imaging, and the molecular orientations of individual molecules were found to depend on both their molecular structures and their local nano-environment. / Graduation date: 2013

Robert Dean Larrabee. / "May 21, 1957." "This report is based on a thesis submitted to the Department of Physics, M.I.T., May 13, 1957, in partial fulfillment of the requirements for the degree of Doctor of Science." / Bibliography: p. 80-81. / U.S. Army Signal Corps Contract No. DA36-039-sc-64637 Dept. of the Army Task 3-99-06-108 Project 3-99-00-100