Facile synthesis and the sensitized luminescence of europium ions-doped titanate nanowires

Europium (Eu) ions-doped titanate nanowires were synthesized via a sol-gel-hydrothermal chemistry and they were found to be roll multilayered trititanate-type nanowires intercalated with Eu³⁺ and alkali ions. The average diameter was about 20 nm for nanowires synthesized in NaOH solution and about 10 nm for nanowires synthesized in KOH solution. Under ultraviolet excitation the nanowires showed bright red emission corresponding to ⁵D₀-⁷F_j of Eu³⁺ ions at room temperature, which was attributed to the non-radiative energy transfer from the surrounding Ti-O octahedral nanosheets to the central Eu³⁺ ions in interlayer. The luminescent properties of nanowires were influenced by the type of co-intercalated alkali ions, doping degree, hydrothermal and annealing temperatures. The intensity ratio of ⁵D₀-⁷F₂ to ⁵D₀-⁷F₁ of titanate nanowires intercalated with Eu³⁺ and Na⁺ ions was higher than that of titanate nanowires intercalated with Eu³⁺ and K⁺ ions. The emission intensity increased with Eu³⁺-doping degree and reached a quenching level about Eu/Ti = 15 mol%. The excitation efficiency from nanosheets to Eu³⁺ ions increased with hydrothermal temperature. However, annealing samples at high temperature led to the decrease of the excitation efficiency and corresponding emission.