EXAFS study of the Er3+ ion coordination in SiO2–TiO2–HfO2 sol–gel films

The local order around ion-implanted Er3+ ions in SiO2-TiO2-HfO2 thin films prepared by sol-gel, was studied by extended X-ray absorption fine structure at the Er-L-III edge. Both the first and second coordination shells of Er3+ were analyzed for different heat-treatments. While the first coordination shell always consisted of similar to 6-7 oxygen atoms at distances varying between 2.23 and 2.27 angstrom, the Structure of the second shell was found to vary with the film composition and heat-treatment. Namely, whereas Si was found to be the only second neighbor of erbium in binary SiO2-TiO2 films, the addition of HfO2 caused a preferential replacement of Si by Hf. The post-implantation thermal treatments also played a fundamental role in determining the final environment of the erbium ions. (C) 2008 Elsevier B.V. All rights reserved.