Sensitized Luminescence of Sm³⁺,Eu³⁺-Codoped TiO₂ Nanoparticles

Sm³⁺,Eu³⁺-codoped TiO₂ nanoparticles were prepared by a facile sol–gel-solvothermal method. Sm³⁺ and Eu³⁺ were successfully incorporated into a TiO₂ lattice and resulted in intense emission lines with resolved crystal-field splitting, in spite of a large mismatch in ionic radius between trivalent lanthanides (Ln³⁺) and Ti⁴⁺. The intense sensitized emissions of Sm³⁺ and Eu³⁺ ions by TiO₂ host were obtained at room temperature. In this case, Sm³⁺ also acts as a bridge to transfer energy from TiO₂ host to Eu³⁺ ions, which was not observed in Eu³⁺-doped TiO₂ nanoparticles. In comparison with direct excitation of lanthanide ions, the luminescence lifetimes of ⁴G_5/2 of Sm³⁺ and ⁵D₀ of Eu³⁺ were observed to be significantly prolonged upon excitation above TiO₂ band-gap. A sensitization mechanism to illustrate the energy transfer from TiO₂ to Sm³⁺ and Eu³⁺ was proposed based on the optical behaviors of the codoped nanoparticles.