STUDY OF THE REDUCTION REOXIDATION CYCLE IN A LA/CE/TB MIXED-OXIDE

The redox behavior of a La/Ce/Tb mixed oxide used as a precursor for preparing green emitting phosphors has been investigated by means of temperature programmed reduction mass spectrometry (TPR-MS), oxygen pulse/temperature programmed oxidation (TPO), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The experimental conditions ensuring the complete reduction of the starting oxide to a Ce(III) and Tb(III) containing phase have been established. In accordance with the XRD study, the reduced phase consists of a hexagonal, A-type, mixed sesquioxide. The quantitative O2 pulses/TPO data for the reoxidation of this sesquioxide phase are consistent with the formation of a fully oxidized: La2O3/CeO2/TbO2 mixed oxide. Neither the XRD study nor the HRTEM images suggest the occurrence of phase segregation phenomena.