Alkaline terbium tungstates were investigated as a green-light-emitting phosphor for n-UV LEDs. We prepared the compounds using a solid-state reaction, and investigated their luminescence properties. We also investigated the effect of substitution by alkali metal ions and Mo6+ ions to improve the emission intensity. The synthesized phosphors showed sharp excitation and emission spectra due to the 4f-4f electronic transition of the Tb3+ ions. The luminescence intensity was increased by substituting with Na+ ions and K+ions at concentrations of 40% and 6%, respectively. However, the emission intensity substantially decreased by substituting with Mo6+ ions. We considered that this is due to shifting of the 5d level in the Tb3+ ions by increasing the substituted ion content.
Titanium dioxide flakes, serving as a starting material, were prepared by peeling off titanium dioxide coated on a mica substrate. Black substrates were prepared by reducing the titanium dioxide flakes, followed by coating the black substrates with a predetermined amount of titanium dioxide. Various pigments, each exhibiting colors due to optical interference even on white paper, could be obtained. By preparing black substrates in this way, we could obtain an iridescent pigment that absorbed transmitted light in the same way as a coating film formed on a black base layer. The hue of the resulting pigment could also be controlled. As the amount of a titanium tetrachloride solution added dropwise to the black substrates was increased, that is, as the amount of titanium dioxide coated on the surfaces of the black substrates was increased, the reflection peak of the spectral reflectance curve shifted to longer wavelengths. When black substrates having a thickness of 140 nm were used as the starting material, the hue changed from purple, to blue, green, yellow, gold, and red as the amount of coated titanium dioxide coated was increased. For black substrates having a thickness of 220 nm, the hue changed from magenta, to purple and green. The results of measuring the thicknesses of the pigment flakes showed a correlation between the total thickness and the hue produced by optical interference. In addition, the black titanium dioxide substrates used as the starting material were strongly photocatalytic. However, we also found that the photocatalytic properties could be decreased by the reduction process and by a silica-coating process performed in the production of the black substrates.