Bulk yttrium oxysulfide phosphors were prepared using the polysulfide flux method. The morphology and structure was characterized using transmission electron microscopy and x-ray powdered diffraction. Visible emissions occurring near 530 and 550 nm and 660 - 670 nm consistent with the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively, were observed under 808, 980, and 1560 nm excitation. The upconverting mechanisms excited at 808, 980, and 1560 nm have been investigated in detail. The power dependent behavior of the upconverted emission intensities for singly doped erbium phosphors excited at 808 and 980 nm indicated a two-photon excitation process. Likewise, the ytterbium and erbium co-doped phosphors excited at 980 nm also indicated a two-photon excitation process. Doping with 10% erbium showed the most intense emissions under 808 and 1560 nm excitation. Yttrium oxysulfide co-doped with 15% ytterbium and 3% erbium showed the most intense emissions under 980 nm excitation. Upon 1560 nm excitation, the intensity of the red emission band was significantly enhanced by co-doping erbium with ytterbium. Concentration quenching became apparent when either the concentration of erbium or ytterbium reached 20%.

Materials with potential for high temperature inorganic pigment applications (e.g. ceramics) have been synthesised using solid state methods and characterised using powder X-ray and neutron diffraction, magic angle spinning NMR, Mossbauer spectroscopy, UVNis spectroscopy and colour measurement techniques. A number of compounds containing tin (H) and niobium (V) have been modified and doped with various constituents to tailor and widen the colour properties of the bright yellow parent phases. The dark yellow (L*(91.28), a*(13.74), b*(54.76)) tin niobium oxide pyrochlores have been re-characterised using neutron diffraction techniques. These materials exhibit both cation and anion disorder caused by a stereoactive lone pair on the tin (H) metal centres. Solid state NMR and Mossbauer studies have shown the presence of tin (IV) on a symmetric site within the primary phase of the pure oxide pyrochlore and methods have been investigated to minimise the tin (H) disproportion method from where the tin (IV) is derived.