Photoluminescence in rare earth activated oxides and II-VI chalcogenides
This thesis is concerned with the luminescent properties Â·of rare earth doped oxides and the IT-VI chalcogenide CaCdS. Both materials are luminescent by very different mechanisms. Luminescence from CaCdS is due to transitions between the conduction and valence band. Emission spectra were found to be much sharper than in previously reported work. The narrowness of the peak appears to coincide with a reduction in particle size. With increasing cadmium concentration, this short wavelength (370 nm) emission band became distorted in symmetry and exhibited a red shift. This was seen as being indicative of a solid solution in which Cd substituted into the Ca sublattice. The excitation and emission mechanisms of rare earth doped materials are distinctly different from those of the IT-VI chalcogenides. Rare earth emissions consist of narrow emission bands which are predominantly due to transitions within the sheilded 4f orbital The visible emission spectra measurements of rare earth doped YÂ£J3, YV04' Gd202S and Y202S phosphors under 244 nm and 257 nm excitation were undertaken in order to examine the mechanisms of their emission processes. 1bis makes possible a comparison with the upconversion visible emission spectra that are obtained from these phosphors when they are excited with red light of 632.8 nm. .The motivation for this research was to develop improved phosphors for lighting applications that can be excited in the ultraviolet region.
Networked Digital Library of Theses and Dissertations