Physico-chemical environment of Al impurity atoms in amorphous silica

The physico-chemical environment around the aluminum impurity atoms in commercial Herasil silica is studied by electron-induced X-ray emission spectroscopy. Despite the low concentration of aluminum and the charging effect occurring upon electron irradiation, we have been able to characterize the environment of the Al atoms. We show that the Al atoms are in an octahedral environment, i.e. surrounded by 6 oxygen atoms. The presence of Al clusters, whose metallic character would make them candidates to be ultraviolet absorption centers, is ruled out.