Multisite luminescence of rare earth doped TiO2 anatase nanoparticles

Eu3+, Sm3+ and Tb3+ ions have been incorporated into anatase TiO2 nanocrystals via hydrolytic sol–gel method. Pure anatase phase was confirmed with XRD and TEM measurements. Band gap energies change slightly with rare earth incorporation, from 3.32 eV for undoped TiO2 to 3.15 eV, 3.25 eV and 3.29 eV for Tb3+, Sm3+ and Eu3+ doped TiO2. Photoluminescence of Eu3+ and Sm3+ originated from three different sites in TiO2 nanocrystals have been identified with the laser-excited site-selective spectroscopy measurements at 10 K. One site exhibits broad emission peaks, which are ascribed to the distorted lattice site near the surface. Other two sites, associated with the inner lattice, show significantly sharper fluorescence lines as a consequence of an ordered crystalline environment. The emission decays of Eu3+ and Sm3+ have similar values for inner-lattice sites and longer lifetimes for near-surface sites. The luminescence of Tb3+ doped TiO2 nanocrystals was immeasurably weak.