Precipitation techniques and characterisation of rare earth element doped phosphor materials
The work in this thesis had two main aims. The first aim was to study the use of a number of precipitation methods to control the size and morphology of precursor phosphor materials for potential applications in a new generation of high definition and field emission displays. The morphological and luminescent characteristics of these precursor phosphor materials were studied after they were annealed to form their respective luminescent oxides using electron microscopy and light measuring techniques. The first set of experiments presented describes the development of a range of spherical submicron europium-doped yttrium oxide phosphor particles and their optimisation for use in the aforementioned applications. A homogeneous precipitation technique exploiting a hydrothermal decomposition of urea that provides hydroxycarbonate phosphor precursor ligands is at the centre of this work. In the presence of rare earth element nitrates the hydroxycarbonate ligands form spherical phosphor precursor particles that after annealing yield the luminescent oxides. This is followed by the presentation of a novel synthetic method using a micellar phase of rare earth element chlorides, after annealing, yielding europium-doped yttrium oxide. This method produces a variety of morphologies with crystallites as small as a few nanometres and up to hundreds of nanometres. Next is described a new precipitation method using ammonia and carbon dioxide gases that are introduced in a controlled manner into a solution of rare earth element chlorides at room temperature. Rare earth element hydroxycarbonates rapidly precipitate upon supersaturation, yielding a range of morphologies and particles sizes. The second aim of the thesis was to prepare a novel range of three-dimensional photonic band gap materials composed of conventional phosphor materials.
RS Pharmacy and materia medica, TP Chemical technology
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