Crystalline-phase dependent red luminescence of TiO₂ : Eu^3\bplus particles prepared by a sol–gel method

Abstract

Crystalline phase and photoluminescence spectra of Eu³⁺-doped TiO₂ particles prepared by a sol–gel method have been investigated at room temperature. X-ray powder diffraction patterns and transmission electron microscope images reveal that amorphous, anatase and rutile phases appear and the grain size becomes larger with the increase of annealing temperature. Under the excitation with a He-Cd laser (325 nm), the well-known ⁵D₀ → ⁷ F _J (J = 0, 1, 2, 3, 4) transitions exhibit broad luminescence bands for amorphous and rutile phases, and sharp luminescence lines for the anatase phase, respectively. The correlation between the crystalline phases and the luminescence properties is discussed on the basis of the symmetry around the Eu³⁺ ions.