Energy Transfer in Bi- and Er-Codoped Y2O3 Nanocrystals: An Effective System for Rare Earth Fluorescence Enhancement

The enhancement of the low absorption cross section and widening of the absorption range of the RE ions in the UV-blue region is still a challenge to develop optical systems with high performance. In this work we synthesized Bi- and Er-codoped Y 2 O 3 nanocrystals by means of Pechini type sol–gel process. X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) were performed to evaluate the nanocrystalline particle size and phase. Photoluminescence investigation in the UV–vis and IR regions showed that the presence of Bi 3+ ions promotes the strengthening of Er 3+ emitter properties. In particular, an Er 3+ sensitization process based on a broadband energy transfer mediated by the Bi 3+ ions in the C 2 site was evaluated, resulting in a wavelength spread for the photostimulation of the rare earth emissions in the visible and NIR range. We pointed out a resonant type via a dipole–dipole interaction as the most probable mechanism of energy transfer. Moreover, the critical distance between the Bi 3+ and Er 3+ ions was estimated to be of about 8.5 Å.