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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Luminescence spectroscopy of natural and synthetic REE-bearing minerals

Friis, Henrik January 2009 (has links)
This study investigates the photoluminescence (PL), cathodoluminescence (CL), radioluminescence (RL) and ionoluminescence (IL) of natural and synthetic minerals. The natural minerals (fluorapatite, leucophanite, meliphanite and zircon) are mostly from Ilímaussaq Alkaline Complex in South Greenland, Langesundsfjord in Norway and from different localities within Scotland. Synthetic fluorapatite (manufactured as part of the present study) and zircon doped with rare earth elements (REE) were used to compare single and multidoped materials. This study has shown that many of the generally accepted applications of luminescence are not as straightforward as often suggested by the current literature. For example, the study demonstrates how site distribution of REE, based on luminescence, is greatly affected by the dopant level and structural changes, and that different conclusions can be drawn on the same sample depending on method applied. Furthermore, it is clearly demonstrated that using luminescence as a tool for quantitative trace element determination is not going to be a standard technique in the near future if ever. The two main findings supporting this conclusion are the non-linear intensity decrease between different REE activators in the same sample and a large variation between activators at the concentration at which self-quenching starts. In contrast to the general perception that luminescence related to REE is mostly independent of the host, this study has shown a strong interaction between host and REE activators. This conclusion is supported by the change in the activator’s coordination polyhedron observed with single-crystal and powder X-ray diffraction combined with full chemical characterisation. When combining the weak interaction between some REE with the strong host interaction this study has shown the potential for designing new types of colour tuneable and “white light” LEDs based on natural minerals. This study also reveals that zircon doped with Gd³⁺ and Eu³⁺ can potentially have quantum-cutting properties.
2

Fundamental and sedimentological controls on luminescence behaviour in quartz and feldspar

King, Georgina January 2012 (has links)
The optically stimulated luminescence (OSL) characteristics of a suite of quartz and feldspar samples from a range of modern glaciofluvial sediments have been explored to determine the use of OSL as a depositional pathway tracer. Paraglacial and subglacial source material and various glaciofluvial deposits have been analysed from the glacial catchments of Bergsetbreen, Fåbergstølsbreen, and Nigardsbreen as well as the Fåbergstølsgrandane sandur, Jostedalen, Norway. The OSL distribution signatures have been characterised through exploration of sample skewness, kurtosis and overdispersion, and dose distributions of the different depositional settings and source materials are distinct for both quartz and feldspar. Residual ages are greatest for feldspar, indicating significant potential age overestimation where feldspar is used to date glaciofluvial deposits. Sample dose distributions and overdispersion characteristics are driven by source sediment properties, whereas residual ages are controlled by transport and depositional processes. Those transport and depositional processes which result in significant light exposure, also influence dose distributions, and processes that sort sediments least effectively have the highest residual doses. Sample OSL characteristics, transport distance and grain size distributions have been investigated using factor analysis, as a means of predicting sediment source, facies, depositional process and deposit type. Although the depositional processes of the quartz samples can be clearly differentiated based upon OSL characteristics, factor analyses of feldspar and grain size characteristics are inconclusive. The application of quartz OSL to the Norwegian samples was limited by its very poor luminescence sensitivity. Quartz is the preferred mineral for OSL, however, despite the plethora of successful quartz OSL applications, the precise origin of the UV/blue luminescence emission, measured during OSL, remains unclear. The origins of this emission and controls on its intensity were explored using a variety of spectroscopic techniques including photoluminescence, cathodoluminescence, radioluminescence (RL), ionoluminescence (IL) and x-ray excited optical luminescence (XEOL). Exciting sample luminescence at a range of energies enables exploration of the different donor centres responsible for the luminescence emission. Cathodoluminescence and RL emission spectra are similar, comprising broad emissions at 1.5, 2.0 and 2.7 eV (detection in the UV part of the spectrum was not possible for these experiments). Ionoluminescence emission spectra were dominated by the ~ 3.3 eV emission, which is a component of the signal conventionally monitored during OSL. This emission depleted as a function of dose, to the benefit of the red emission (1.8-2.0 eV) for all samples throughout IL, and similar observations were made for the 3.4 eV emission observed from the XEOL emission spectra. The XEOL spectra are dominated by an emission at ~ 3.8 eV, not widely reported for quartz, which has tentatively been attributed to peroxy linkages. Differences between the IL and XEOL emission spectra are interpreted as evidence for the presence of multiple excited states.

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