Ultraviolet photoelectron spectra of Er2@C82 (I), Er2@C82 (III), Er2C2@C82 (I) and Er2C2@C82 (III)

Abstract

Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two erbium atoms and an erbium-carbide cluster entrapped fullerenes, Er2@C82 (I), Er2@C82 (III), Er2C2@C82 (I) and Er2C2@C82 (III), were measured using a synchrotron radiation light source and MgKα X-ray gun. The spectral onset energy of these endohedral fullerenes is around 0.8–0.9eV, which is larger than that of Er@C82 (I) of 0.4eV. The UPS of erbium atoms encapsulated endohedral fullerenes having the same C82 cage structure were analogous while those of the different cage structure are different. This finding supports an empirical rule that the electronic structure of the endohedral fullerenes is principally governed by the C82 cage structure. The XPS Er4d5/2 peak of Er2@C82 suggests the oxidation state of (Er3+)2 @C826-. The difference spectrum between the UPS of Er2@C82 (III) and Er2C2@C82 (III) has the same C3v structure reveals two excess electrons on the cage of Er2@C82.