Influence of surface coating on physical properties of TiO₂/Eu³⁺ nanocrystals

Abstract

The sol−emulsion−gel method is used for the preparation of Eu₂O₃-doped and -coated TiO₂ nanocrystals. Here, we report the control of the crystal phase composition and crystallite size as a function of the temperature of heating and surface coating. A significantly higher anatase phase (100%) has been obtained at 800 °C heated sample, and this anatase phase is stable up to 22 nm size. Due to surface coating of TiO₂ nanocrystals by Eu₂O₃, we obtained 27% anatase phase at 1000 °C heated sample, which is new observation in this study. The lattice volume decreases with decreasing the particle size for anatase particle and a nonlinear size dependency of lattice parameters is obtained at size < 10 nm. However, the lattice volume increases with decreasing the particle size in rutile phase. Again, we obtained that the lattice strain of doped (tensile) sample is different from coated (compressive) sample. The mechanism related to morphology control for doped and coated (TiO₂:Eu) nanoparticles is proposed and discussed. The growth mechanism is different for coated and doped (orientated attachment) nanocrystals. It is also found that photoluminescence properties of Eu³⁺ ions are sensitive to the crystal structure which is again controlled by the surface coating and temperature of heating. The emission intensity of the peak at 614 nm (⁵D₀ → ⁷F₂) for Eu³⁺ ions for coated TiO₂ nanocrystals is greater than doped sample.