Structural and optical properties of europium- and titanium-doped Y₂ O₃ nanoparticles

Luminescent nanoparticles of Y₂ O₃ doped with europium (Eu) and/or titanium (Ti) were synthesized using modified sol-gel routes. The crystalline cubic phase was confirmed using X-ray powder diffraction (XRD). Particle morphology and size were evaluated using scanning and transmission electron microscopy. High-resolution transmission electron microscopy showed that the synthesis method affected the average particle size and the Fourier transform of the images showed the lattice plane distances, indicating that the samples presented high crystallinity degree in accordance with the XRD pattern. The Ti valence was investigated using X-ray absorption near edge spectroscopy and the tetravalent form was the dominant oxidizing state in the samples, mainly in Eu and Ti co-doped Y₂ O₃ . Optical behaviour was investigated through X-ray excited optical luminescence and photoluminescence under ultraviolet-visible (UV-vis) and vacuum ultraviolet (VUV) excitation. Results indicated that Eu³⁺ is the emitting centre in samples doped with only Eu and with both Eu and Ti with the ⁵ D₀ →⁷ F₂ transition as the most intense, indicating Eu³⁺ in a noncentrosymmetric site. Finally, in the Eu,Ti-doped Y₂ O₃ system, Ti³⁺ (or Ti^IV ) excitation was observed but no Ti emission was present, indicating a very efficient energy transfer process from Ti to Eu³⁺ . These results can aid the development of efficient nanomaterials, activated using UV, VUV, or X-rays.