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 Y2O3 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 Bi3+ ions promotes the strengthening of Er3+ emitter properties. In particular, an Er3+ sensitization process based on a broadband energy transfer mediated by the Bi3+ 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 Bi3+ and Er3+ ions was estimated to be of about 8.5 angstrom.