Investigação do estado de oxidação dos íons európio e titânio incorporados na matriz vítrea aluminosilicato de cálcio

Abstract

In this work, we investigated the influence of the composition of calcium aluminosilicate glass on the formation of different oxidation states of rare earth europium (Eu) and transition metal titanium (Ti), embedded in glasses with doping oxides Eu2O3 and TiO2. Two sets of samples with different compositions were prepared. In both series, doping concentration were kept fixed at 2.5 wt% Eu2O3 and 2 wt% TiO2, and the silica concentration was increased in the glass. Techniques such as XANES (X - Ray Absorption Near Edge Structure), optical transmission spectroscopy, photoacoustic spectroscopy, electron paramagnetic resonance, luminescence spectroscopy, density and refractive index measurements were performed to characterize the samples. The results showed the evidence of a reduced valence of the ions studied with increasing silica content. This behavior can be related to a reduction in the non-bridging oxygen number on the network. In addition, the results suggest that in glasses with low concentrations of silica, the Europium (II) predominantly occupies sites with high symmetry and strong interaction with crystal field. Moreover, in the sample with lower silica content, X-ray absorption data suggest Ti (IV) occupies sites with tetrahedral symmetry, whereas for higher silica content, there are indications of sites where Ti (IV) is coordinated by five oxygens.