Local environment of rare-earth dopants in silica-titania-alumina glasses: An extended x-ray absorption fine structure study at the K edges of Er and Yb

We have applied extended x-ray absorption fine structure (EXAFS) spectroscopy to the K edge of rare earths (RE) in a study of the local environments of diluted Er and Yb dopants in silicate glasses, prepared by sol-gel processing. Silica-titania-alumina glasses, doped with RE ions at and above the luminescence quenching concentration were investigated and EXAFS spectra were recorded in a wide k range up to 160 nm(-1) not obtainable when working at the L-III edge. No direct RE-RE correlations were found, providing a strong support for previous studies. A model of RE aggregation derived from these observations is also discussed.