Extended X-ray absorption fine structure measurements of the local environment of Pr³⁺ ions in silica xerogels and zinc borate glasses

The local environment around Pr³⁺ ions in a silica xerogel, densified at 950°C, and in 4ZnO · 3B₂O₃ glasses doped with different Pr concentrations (from 0.5 up to 8 mol%) has been studied by X-ray absorption spectroscopy at the Pr L₃-edge. The radial distribution functions (RDF) in the region of the first coordination shell of praseodymium, i.e. the nearest group of oxygen atoms, were reconstructed using a model-independent approach. Both in the xerogel and in the glasses, the RDFs are broad and asymmetric, with a tail on the long distance side and a coordination number ranging between 6 and 7. The RDF of the xerogel is broader and more symmetric and shows a coordination number slightly lower than in the glasses. The local environment of Pr³⁺ in 4ZnO · 3B₂O₃ glass does not change as a function of the praseodymium content.