Mechanisms of photoluminescence in cerium oxide pellets with different types of defects

We systematically investigated the photoluminescence (PL) spectra of sintered pellets of cerium oxide, CeO2. The crystal defects were controlled by commonly used techniques in the field of solid-state ionics. We observed the transitions between the O-2p and Ce-4f energy levels in intrinsic CeO2. By doping with trivalent lanthanide ions, which results in oxygen vacancies by charge compensation, a new transition band appears. It involves electronic levels that are similar to those of Ce2O3 clusters, rather than to those of oxygen vacancies. In reduced cerium oxide CeO2-& delta;, where the number of Ce3+ ions is larger, electrons partially fill the energy levels of defects similar to Ce2O3 clusters, and thus an optical response derived from the Ce-4f-Ce-5d transition appears.