Evidence of Trivalent Europium Incorporated in Anatase TiO2 Nanocrystals with Multiple Sites

Trivalent europium ions have been successfully incorporated in anatase TiO 2 nanocrystals via a sol−gel solvothermal synthesis, in spite of a large mismatch in ionic radius between Eu 3+ and Ti 4+ . The photoluminescence intensity of Eu 3+:TiO 2 nanocrystals has been significantly improved, which is comparable to that of common red phosphors. Multiple sites of Eu 3+ in TiO 2 nanocrystals have been identified by the technique of site-selective spectroscopy. Eu 3+ ions at two lattice sites exhibit sharp emission and excitation peaks with site symmetries descending from D 2d to approximate C 2v and D 2 as a result of the lattice distortion, whereas Eu 3+ ions at disordered site near the surface are analogous to Eu 3+ ions located in a glasslike environment. Extended X-ray absorption fine structure is utilized for identifying the local structure and Eu 3+ coordination. The luminescence dynamics and crystal-field levels of Eu 3+ at different sites have been analyzed. A growth mechanism for the incorporation of Eu 3+ in the anatase lattice is also suggested.