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 degrees C, and in 4ZnO . 3B(2)O(3) glasses doped with different Pr concentrations (from 0.5 up to 8 mol%) has been studied by X-ray a bsorption spectroscopy at the Pr L-3-edge. The radial distribution fun ctions (RDF) in the region of the first coordination shell of praseody mium, 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 s ide 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 4 ZnO . 3B(2)O(3) glass does not change as a function of the praseodymiu m content. (C) 1998 Elsevier Science B.V. All rights reserved.