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

Abstract

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.

Multisite luminescence of rare earth doped TiO2 anatase nanoparticles

“…Photoluminescence emission properties of rare earth doped TiO 2 is investigated by means of laser excited high resolution site-selective spectroscopy at low temperature (10 K) doped anatase (Fig. 7) confirm reported findings in [32,33] (number of sites and site symmetries) and the same three-site structure has been proved for Sm 3þ doped TiO 2 sample (see Fig. 8 Figs.…”

“…It is interesting to note that emission lifetime from disordered site, both for Eu 3þ and Sm 3þ , is longer than lifetime from higher symmetry sites II and III. Eu 3þ emission decays are slightly higher compared to the previous findings [32].…”

The Electronic Structure of Lanthanide Impurities in TiO2, ZnO, SnO2, and Related Compounds

“…20 suggesting that the Eu 2+ ground state is located inside the conduction band. Similarly Luo et al 21 attributes a small hump at 3.6 eV in the 10 K excitation spectrum to E CT (6, 3+, A). In Fig.…”

Spectroscopic and crystal-field analysis of energy levels of Eu3+ in SnO2 in comparison with ZrO2 and TiO2

“…Sometimes the actual symmetry can be somewhat lowered as a result of the lattice distortion caused by the ionic radii mismatch between the substituted and substituting ions and presence of the charge compensating oxygen vacancies near impurities. As an example, we mention here that in TiO 2 :Eu 3+ nanocrystals the site symmetry was changed from D 2d to D 2 or C 2v [12]. The generalized description of the M 4+ site symmetries in the considered three MO 2 compounds allows for identification of four possible local symmetries of the M 4+ sites: tetragonal, orthorhombic, monoclinic and triclinic [4].…”