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-LIII edge. Both the first and second coordination shells of Er3+ were analyzed for different heat-treatments. While the first coordination shell always consisted of ∼6–7 oxygen atoms at distances varying between 2.23 and 2.27 Å, 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.