Raman and EXAFS study of Neodymium and Praseodymium included alumino germinate glass

Abstract

Germanate glass has been synthesised keeping Al2O3 fixed at 10 mol% with Neodymium oxide and Praseodymium oxide varying from 5 mol% to 10 mol%. The effect of the rare-earth inclusion on the structure of the host matrix was examined by several techniques. Extended x-ray Absorption Fine Structure showed tetrahedral coordination of oxygen around Ge for all the glasses and gave the oxygen coordinations around Nd and Pr to be 8.7 and 8.9 respectively which is in contrast to the often quoted octahedral coordination for these ions. Raman spectroscopic studies have shown the Qn linkages of the GeO4 tetrahedra in these glasses as predominantly Q2 and Q3. The distribution of relative fractions of these linkages shows the Pr containing glass as having a few Q° and maximum Q2 connectivities while for the Nd and Nd-Pr containing glasses, these distributions peak for the Q3 connected linkages. These observations lead to the view that the Pr containing glass has a less well connected network than the Nd containing glasses. The presence of Pr in these glasses results in a decrease in electronic band gap energy and an increase in the electronic polarizability.