Europium doped titanium dioxide nanocrystalline: synthesis, structure and optical properties

Uniform, spherical-shaped TiO2: Eu nanoparticles with different doping concentrations were synthesized using the sol-gel method. The structural, morphology, optical, luminescent, and surface properties of the samples were investigated at different Eu3+ concentration. The morphology, crystalline structure, and chemical composition of the samples were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The X-ray diffraction results reveal that the obtained powder nanoparticles consist of a single phase tetragonal structure. The crystallite sizes calculated by utilizing Scherrer’s equation were found in the range of 18.94 – 7.77 nm for TiO2:Eu samples annealed at 550οC. The SEM images reveal an irregular agglomerated morphology indicating a decrease in particle size with an increase in Eu3+ concentration. X-ray photoelectron spectroscopy (XPS) high resolution spectra of the Ti-2p peak confirmed that Ti atoms were in a doubly ionized state, and the deconvolution of the O1s XPS peak show the presence of oxygen related defects in the sample. EDS results confirm a systematic increase of Eu content in the as-prepared samples with the increase of europium concentration. Incorporation of europium in the titania particles induces a structural deformation and a blueshift of their absorption edge. The luminescence intensity increases with Eu3+ concentration up to 3 mol% and then quenched. While the PL emission of the as-grown samples is dominated by the 5D0 - 7Fj transition of Eu3+ ions, the emission intensity reduces drastically after thermal annealing due to outwards segregation of dopant ions.