Hydrothermal Synthesis of Nb- and Eu- Co-Substituted Nanocrystalline Anatase: Eu_xTi_(1-2x)Nb_xO_2 with Photoluminescence and Photocatalytic Activity: Compositional Dependence of Multifunctional Properties

摘要

Nanocrystalline titania (Eu_xTi_(1-2x)Nb_xO_2. X = 0-0.15) co-substituted with europium (Eu) and niobium (Nb) having photoluminescence (PL) and photocatalytic activity was formed as a single phase of anatase-type structure from the precursor solutions of TlOSO_4, NbCl_5, and EuCl_3 under mild hydrothermal conditions using the hydrolysis of urea. The amount of Eu and Nb that can be co-doped into a metastable anatase-type TiO_2 lattice under hydrothermal conditions was limited up to 15 mol%, respectively, above which the aeschynite EuTiNbO_6 coexisted with anatase. The nanocrystalline titania can be excited by ultraviolet light 395 nm (f-f transition) and emits red light (611 nm) with line spectrum corresponding to ~5D_0-~7F_2 transition. The PL intensity increased with increased replacement amount of Eu and Nb. The anatase solid solution co-doped with 5 mol% Eu and 5 mol% Nb (x = 0.05) showed a similar activity to pure anatase (x = 0) on the photodecomposi-tion of methylene blue under UV light irradiation. The ana-tase-to-rutile phase transformation was delayed via the copresence of Eu and Nb component. In the course of heating and the growth of anatase crystallite, a part of the dopants that could not exist in the titania precipitated as euxenite phase EuTiNbO6 from the anatase at 900℃-1000℃ before the phase transformation.