The structural environments of Er3+ ions were studied by extended X-ray abs
orption fine structure (EXAFS) measurements above the Er L-III edge, in SiO
2-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 th
e second Er3+ coordination shells were analyzed. The first co-ordination sh
ell was composed of similar to6 -7 oxygen atoms at distances varying betwee
n 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 tetrahedr
ally co-ordinated second near neighbor (SNN) atoms, bonded through corner-s
haring Er-O-SNN bridges. The SNN species were found to be either Si. or a c
ombination of Si and At, depending on the matrix composition. Although the
measured lifetime values for the Er3+ fluorescence at 1.54 mum varied betwe
en ca. 0.5 and 5.0 ms, depending on the Al content and indicated the occurr
ence of Er3+ concentration quenching above 0.5 at.% Er in films co-doped wi
th 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 n
m). This suggests that there was no rare-earth (RE) clustering in the prese
nt films, but that certain mechanisms of RE ion-ion interactions at longer
distances were active. (C) 2001 Elsevier Science B.V. All rights reserved.