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The research in this project was directed, firstly towards gaining an understanding of the effect excited-state absorption (ESA) has on gain and lasing in broadly tunable Ce:LiLuF lasers and secondly towards the development of Ce:LiLuF lasers suitable for spectroscopic applications. Detailed measurements of the single-pass, small-signal gain in Ce:LiLuF were undertaken, with a gain coefficient as high as 30±1 cm^-1 at 309 nm, with an absorbed pump fluence of 0.46 Jcm^-2. Further, the ESA in Ce:LiLuF at 261 nm and 349 nm was measured. Using both the gain and ESA results in a computer model, the effective gain cross-sections at 309 nm and 327 nm and the ESA cross-sections at 261 nm, 309 nm, 327 nm and 349 nm were determined. The ESA cross-sections were found to be of the order of 10^-18 cm². The effective gain cross-section in Ce:LiLuF was found to increase with decreasing temperature. This was proposed to arise from a decrease in the ESA cross-section with decreasing temperature in the Ce:LiLuF. An in-depth parametric study of Ce:LiLuF laser operation and tunability was undertaken. The results of these studies, together with computer modelling, enabled the importance of ESA and other effects on lasing to be established. In particular, the gain competition effects and ESA were found to lead to inefficient laser operation unless σ-polarised lasing was suppressed. With polarisation selection, efficient operation was obtained, with continuous tunability between 305 nm - 335 nm. Narrow bandwidth operation of Ce:LiLuF for use in OH radical detection in the atmosphere was investigated. Narrow bandwidth operation was achieved for the first time in Ce:LiLuF using a Eittrow grating with a telescopic and prism beam expansion system. Tunable lasing between 306.5 nm and 311.5 nm was obtained, with a spectral bandwidth of 0.7 cm^-1. Finally, highly efficient Ce:LiLuF lasing was achieved with a new all-solid-state, 289 nm frequency-quadrupled Raman-shifted Nd:YAG laser. Slope efficiencies as high as 62±3% were achieved. This slope is believed to be the highest obtained in any cerium laser to date. The IR-to-UV conversion efficiency was 0.41% and the UV-to-UV conversion efficiency was 41%. These high efficiencies were attributed to high pump beam quality and good mode matching.

No description available.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

AN ABSTRACT OF THE THESIS OF James Morrow, for the Master of Science degree in Mechanical Engineering, presented on November 3, 2017, at Southern Illinois University Carbondale. TITLE: INVESTIGATION OF THE MATERIAL PROPERTIES OF CERIUM OXIDE WITH DOPANTS FOR AN OXYGEN TRANSPORT MEMBRANE MAJOR PROFESSOR: Dr. Kanchan Mondal Many physical properties of cerium oxide both undoped and doped have been studied herein. These properties include electrical conductivity, hardness, sintered density, and microstructure. These will be used to help determine a cerium oxide compound to use as an oxygen transport membrane in a combustion system. These compounds have been readily studied beforehand with exception to compounds with multiple dopants. Along with single doped cerium oxide, dual doped was investigated as well. The samples to be tested were created using co-precipitation and the subsequent powders were sintered at 1500°C to generate solid pellets. Once the pellets were formed the physical properties were tested. It was found that hardness and sintered density had little to no effect on electrical conductivity and the microstructures of the samples were shown to be favorable. As far as single or dual dopants were concerned, it was found that by including a second dopant along with zirconium that the electrical conductivity was reduced. Except for in the case where iron was doped along with zirconium, where the conductivity was increased. It was suggested to use samarium as the second dopant along with zirconium for the membrane.

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In this work the performance of cerium-based oxygen carriers is investigated in a simulated chemical looping dry reforming system using methane and carbon dioxide as fuel and oxidizing gas respectively. The samples to be studied are pure cerium oxide and cerium oxide doped with zirconium, yttrium, samarium, and scandium more specifically: CeO2, Ce0.8Y0.2O1.9, Ce0.85Y0.05Zr0.1O1.975, Ce0.95Zr0.05O2, Ce0.9Sm0.05Zr0.05O1.975, and Ce0.9Sc0.05Zr0.05O1.975. Characteristics such as crystallography including lattice parameter and particle size of the samples are evaluated using X-ray diffraction (XRD) and particle size analysis. The oxygen transport capacity will also be measured using a thermogravimetric analyzer (TGA). This method of measurement also allowed for insight on oxygen release temperatures as well as recyclability of the samples. The particle size analysis showed that the synthesis method of precipitation-agglomeration resulted in samples with consistent particle size distribution indicating the method can be scaled up. The X-ray analysis of samples before and after the TGA tests show that all the materials tested had a cubic fluorite crystal structure which was maintained through the oxidation reduction cycles. The lattice parameter was found to increase slightly with a loss in oxygen content in the samples. The addition of trivalent dopants resulted in a decrease in the temperature of initiation of reduction in methane. While reduction of commercial ceria initiated near 800 oC. the addition of trivalent dopants resulted in a lowering of the initialization temperature between of 150 – 200oC. The activation energy of commercial ceria was 248.42 kJ/mol for reduction in methane, indicating that the rate controlling mechanism is chemical reaction rather than diffusion. The addition of trivalent dopants resulted in a significant lowering in the activation energy. The activation energies obtained in this study show that the addition of dopant increased the significance of diffusion through the solid and the controlling mechanisms were both diffusion and chemical reaction. Overall, the addition of trivalent dopants enhanced the extent of oxygen exchange in CLDR process.

Cerium oxide (ceria, CeOâ‚‚) is a rare earth oxide that has attracted wide-spread research interest because of its unique properties such as high mechanical strength, oxygen ion conductivity, oxygen storage capacity and autocatalytic property. In recent years, researchers have discovered that ceria nanoparticles (NPs) are capable of protecting cells from free radical induced damage. Interestingly, it was found that nanometer size (~ 5 nm) ceria can scavenge free radicals quite efficiently, thus acting as an anti-oxidant. This phenomenon has been explained based on the autocatalytic property of ceria NPs. Several methods have been developed for the synthesis of ceria NPs that include flame combustion, hydroxide co-precipitation, hydrothermal/solvothermal, microemulsion, sonochemical and microwave-assisted heating methods and sol-gel method. Ceria NPs synthesized by these methods are often highly aggregated. Furthermore, large scale synthesis of monodispersed CeOâ‚‚ NPs is quite challenging. Therefore it is desirable to synthesize ceria NPs in bulk quantity keeping its important properties intact, specifically free-radical scavenging property. The main goal of this study is therefore to synthesize ultra-small ([less than]5.0 nm), high quality monodispersed ceria NPs in large quantities. In this thesis work, I present a couple of room temperature techniques, dilute sodium hydroxide (NaOH) assisted and ethylenediamine (EN) assisted for the synthesis of nearly mono-dispersed, ultra-small ( < 5 nm) and water-dispersible ceria NPs. Morphology and particle size of the ceria NPs were investigated through high resolution transmission electron microscopy (HRTEM). The HRTEM analysis confirmed the formation of 3.0 ± 0.5 nm size and 2.5 ± 0.2 nm size highlycrystalline ceria NPs when synthesized using dilute NaOH and EN as solvents, respectively. The nanostructures were characterized by X-ray diffraction (XRD) studies to determine the crystal structure and phase purity of the products. The samples were also thoroughly characterized by X-ray photoelectron spectroscopy (XPS) to determine the oxidation state of cerium ions. The presence of the +3 and +4 oxidation states in the samples was also confirmed from the XPS analysis. The co-existence of these two oxidation states is necessary for their applications as free radical scavenger. The autocatalytic behaviors of the ceria NPs were investigated through a hydrogen peroxide test and monitored by UV-visible transmission spectroscopy.