Oxygen vacancies, hydroxyl groups and fluorine ions in the local environment of Yb3+ ions doped in CeO2 nanoparticles

The local environment of Yb3+ ions doped into ceria (CeO2) nanoparticles, synthesized by two different methods, was determined using EPR spectroscopy. It was found that the charge compensator for the Yb3+ ion located in the nearest environment can be a vacancy, a hydroxyl group, or a fluorine ion. The EPR spectra of Yb3+ ions at concentrations of 0.1 mol% and 0.5 mol% in ceria nanoparticles, prepared using the coprecipitation technique from an aqueous solution, are mainly due to cubic sites, which indicate the remote location of the charge compensators. The EPR lines resulting from trigonal sites in these samples suggested that the charge compensation is associated with a hydroxyl group. The FTIR measurements correlate with this supposition. After annealing the samples in a vacuum furnace, EPR lines from trigonal sites related to oxygen vacancies were observed. The second type of ceria nanoparticle was prepared by annealing CeF3 nanoparticles in air. EPR spectra of Yb3+ ions at concentrations of 0.1 mol% and 0.5 mol% in these samples revealed that the lines from trigonal sites were mainly associated with fluorine ions in the nearest environment.