Energy migration of the local excitation at the Eu3+ site in a Eu-O chemical cluster in sol-gel derived SiO2:Eu3+ glasses

By using the fluorescence line-narrowing technique, we observed a broad fluorescence band in the vicinity of a resonant line of the D-5(0)--> F-7(0) transition in an Eu3+-doped SiO2 glass synthesized by a sol-gel process. The comparison with a similar line in an Al2O3-SiO2:Eu3+ sol-gel glass revealed the existence of a chemical cluster of Eu3+ and O2- in the tetrahedral SiO4 network. The broad fluorescence band was attributable to an energy migration among the Eu3+ ions for the site-selectively received excitation energy. Also, based on Yokota-Tanimoto's energy diffusion model, the fluorescence decay curves for the D-5(0)--> F-7(2) transition were closely correlated with the energy migration and gel-glass transformation. The gel-shrinkage and reduced interatomic distance between Eu3+ ions due to a thermal treatment at higher temperature definitely resulted in a decrease in the associated lifetime of the initial decay. (C) 2001 American Institute of Physics.