Synthesis and properties of new anatase-type and composite nanophosphors via hydrothermal method

Nanocrystalline titania phosphors co-doped with yttrium, europium, and niobium (Yx−zEuzTi1−2xNbxO2, x = 0, 0.10, and 0.15, z = 0–x) were directly formed as a single phase of anatase-type structure from the precursor solutions of TiOSO4, NbCl5, YCl3, and EuCl3 under mild hydrothermal conditions at 100–240 °C using the hydrolysis of urea. The crystallite size of the anatase synthesized at 240 °C was in the range of 14–20 nm, though it gradually increased with increased hydrothermal treatment temperature. The nanocrystalline titania can be excited by ultraviolet light 395 nm and blue light 465 nm (f–f transitions), and emits orange (590 nm) and red light (611 nm) with line spectra corresponding to 5D0 → 7F1 and 5D0 → 7F2 transitions, respectively. The nanocrystalline anatase synthesized at 120 °C showed the highest photoluminescence intensity in the as-prepared samples. The photoluminescence intensity was improved and the Red-to-Orange (5D0 → 7F2/5D0 → 7F1) (R/O) emission intensity ratio increased from 2.5–2.7 to 3.6–4.0 via the formation of composite particles that consisted of anatase and euxenite phase after heat treatment at 950 °C. The anatase-to-rutile phase transformation shifted to higher temperature via co-doping niobium, yttrium, and europium into TiO2.