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A kinetic study of the reactions of Group VI-B hexacarbonyls with primary amine and halide ligands was undertaken in order to determine the possible mechanisms of these reactions. As well as the expected dissociative pathway, the reactions with the primary amines were seen to proceed by a concurrent pathway which was dependent upon the ligand concentration. Since nitrogen donor ligands are expected to be poor donor ligands, the mechanism proposed was a "dissociative interchange" mechanism which should not be too dependent upon the nucleophilicity of the ligand. Comparison of the rate constants for the amines studied as well as those of the previously investigated Lewis base ligands indicated all such reactions may proceed through the same mechanism. The similarity in rate constants for the ligand-independent and ligand-dependent pathways supports this mechanism. The rate of formation of the final product was seen to be dependent upon the square of the mercuric halide concentration. Therefore, the conversion of Fe(CO)4(HgX)2 to the final product was proposed to proceed by the successive abstraction by each HgX group of two molecules of mercuric halide. These oxidative elimination reactions are related to a chemical model for the intermediate step in the reduction of dinitrogen to ammonia and their similarities and differences are discussed.

Solid-state lightings are becoming the popular choice for lightings due to its higher efficiency, improved colour rendering index and the flexibility of various size and shape. Halide perovskite has tunable colour emission, low disorder and is solution processable making it one of a popular choice as emitters. This thesis demonstrates the versatility of using halide perovskite material in light-emitting diodes. We demonstrate the first working perovskite light-emitting diode at room temperature by introducing thin layer of perovskite emitter which is crucial to confine the inherent free carriers in the material. We show that the 3D lead-halide bulk perovskite is bandgap tunable with emission in the green and red visible spectrum. Light-emitting diodes in the visible spectrum are common however near-infrared emission is a rarity. Lead is a heavy metal which is known for its toxicity. We tackled the issue of toxicity by replacing with tin and demonstrate tunable emission in the near-infrared region. Bulk perovskites have large binding energy which makes it difficult to confine the charges and form radiative recombination which is crucial for emission and efficiency of the device. We move into lower dimensionality perovskites by utilising all-inorganic perovskite nanoplatelets and show emission in the blue region.

by J.K. Galt. / "September 17, 1947." / Bibliography: p. 24. / Army Signal Corps Contract No. W-39-039 sc-32037

Conventionally, metal halide lamps were struck by voltages higher than those required for breaking down the electrodes to ensure successful ignition. These high ignition voltages may hurt the electrodes to some extent, leading to a shorter lamp lifecycle. In practice, the breakdown voltage can be affected by the dark current which occurs when a voltage is applied on lamp before the electrodes have been broken down. A lamp model to account for the dark current is derived from the test results. Three ignition schemes with single-pulse, multiple pulses and step voltage are used for describing the effect of the dark current on the breakdown voltage. Experimental results exhibit that the breakdown voltage can be lowered by applying a higher dark current or allotting more times of dark current to the lamp. The investigation provides useful information for the design of the ignition circuit.

This research attempts to ignite metal halide lamps once with a single-pulse to avoid the problems of uncomfortable light strobes and irregularly high voltage and current stresses on circuit components caused by multiple strikes in conventional electronic ballasts. Metal halide lamps with single-pulse ignition, however, have difficulty in sustaining the lamp arc when operated with a low-frequency square-wave current. Experimental results indicate that the lamp exhibits an extremely small equivalent resistance as the electrode gap has being broken down. In this stage, the ballast has to keep the lamp current not declining to zero in the first half cycle. On the other hand, the lamp acts like open-circuited during commutation when driven by an alternating current. A sufficient energy from the ballast is needed to continue the arc in the next half-cycle. The transition waveform of the lamp arc current after being broken down is analyzed and the required energy for sustaining the lamp arc is calculated accordingly. Based on the investigation results, a starting scenario with appropriately designed circuit parameters for single-pulse ignition can be figured out. The starting scenario has been experimentally implemented on a 70 W metal halide lamp to demonstrate that the metal halide lamp can be successfully started up with single-pulse ignition.

A single-stage high-power-factor electronic ballast with auto frequency searching capability provides a compact and efficient solution for ballasting metal halide lamps. The circuit configuration is originated from the integration of a buck-boost converter and a half-bridge resonant inverter. The buck-boost converter is designed to operate in discontinuous current mode (DCM) to improve the input power factor and at the same time to regulate the output lamp power. The resonant inverter operating at a high frequency is adopted to obtain a high efficiency on the power conversion circuit. The control strategy of auto frequency searching is realized by a microprocessor along with the acoustic resonance detection circuit. To avoid the acoustic resonance, an auto-frequency-searching method is used to search ¡§quite windows¡¨ on operating metal halide lamps with the high-frequency electronic ballast. Provided the acoustic resonance should happen to the lamp on operation, the electronic ballast will automatically change the operating frequency until a stable frequency is located. When the operating frequency has been changed, the duty-ratio of the buck-boost converter is adjusted to regulate the lamp power at the rated value. Experimental tests are carried out on a laboratory with 70-W metal halide lamps to verify the effectiveness of the auto-frequency- searching control.

The acoustic resonance phenomena of metal halide lamps are investigated. A measuring system is set up to examine the effects of the acoustic resonance to the shape of the lamp arc, the lighting energy spectrum, the color temperature, the light output as well as electrical characteristics. Two ballast circuits are built to drive the lamps with the sine-wave current and the square-wave current, respectively. One ballast employs the series resonant inverter to output the sinusoidal lamp current. The other makes use of the full-bridge inverter to drive the lamps with the square-wave current. They are operated over a high-frequency range from 20kHz to 30kHz. For both ballast circuits, the operating frequency and the magnitude of the lamp current can be controlled independently. ¡@¡@The experiments are conducted on the 70-W metal halide lamps. The experimental results show that the spectral energy and the color temperature change more significantly as the acoustic resonance becomes more serious. These effects become less significant when the lamps are driven by the square-wave current. The degree of the acoustic resonance can be identified by detecting the variation of the lamp voltage or the output light. The investigated results of the thesis can provide useful information when a standard of the acoustic resonance is considered.

In this thesis, a novel electronic ballast that includes a repeatedly resonating ignition circuit is proposed for metal halide lamps. The proposed electronic ballast features a two-stage structure that comprises a power factor corrector and a full-bridge inverter used for current control, filtering and ignition. The full-bridge inverter consists of a leg operating at low-frequency with unidirectional switches and a leg operating at high frequency with bidirectional switches. The low-frequency side performs repetitive resonating on the load circuit with inductors and capacitors to accumulate a high voltage for ignition. Adjusting the duty-ratio of the high-frequency side allows for the regulation of the lamp current. The inductors and capacitors in the load circuit function not only producing the high ignition voltage but also filtering out high-frequency components, so that to drive the lamp with a low-frequency square-wave current. The proposed electronic ballast employing the full-bridge inverter with the specially designed control scheme and circuit parameters allows the metal halide lamp to tackle the demanding starting transient and steady state operation. With a simpler circuit structure and a reduced component count, the product cost will be much lower.