Local order around Er3+ ions in SiO2-TiO2-Al2O3 glassy films studied by EXAFS

The structural environments of Er3+ ions were studied by extended X-ray absorption fine structure (EXAFS) measurements above the Er L-III edge, in SiO2-TiO2-Al2O3 sol-gel derived glassy films with varying Er and co-dopant (Al) contents. The I-4(13/2) excited state lifetimes of the Er3+ ion were also measured for selected samples containing equal amounts of Er2O3 and Yb2O3, the latter being added as a fluorescence sensitizer. Both the first and the second Er3+ coordination shells were analyzed. The first co-ordination shell was composed of similar to6 -7 oxygen atoms at distances varying between 0.225 and 0.229 nm, with small Debye-Waller factors, varying between 1.2 and 2.2 x 10(4) nm(2). The second shell was basically composed of tetrahedrally co-ordinated second near neighbor (SNN) atoms, bonded through corner-sharing Er-O-SNN bridges. The SNN species were found to be either Si. or a combination of Si and At, depending on the matrix composition. Although the measured lifetime values for the Er3+ fluorescence at 1.54 mum varied between ca. 0.5 and 5.0 ms, depending on the Al content and indicated the occurrence of Er3+ concentration quenching above 0.5 at.% Er in films co-doped with 9% Al, no Er-Er interactions were detected by EXAFS in films doped with up to 1.75%., Er, within the sensitivity of this technique (similar to0.5 nm). This suggests that there was no rare-earth (RE) clustering in the present films, but that certain mechanisms of RE ion-ion interactions at longer distances were active.