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

► UPS of Er atoms encapsulated fullerenes with the same cage structure is analogous. ► The UPS Eonset of Er2@C82 (I, III) and Er2C2@C82 (I, III) is around 0.8-0.9 eV ► The XPS Er4d5/2 peak of Er2@C82 suggests the oxidation state of (Er3+)2@ C826-. ► The amounts of electrons on C82 of Er2@C82 are different from those of Er2C2@C82.