INVESTIGATION ON THE VALENCE STATE OF Ce ATOM IN BULK AND NANOCRYSTAL CeO2 BY X-RAY ABSORPTION AND PHOTOEMISSION

Valence band photoemission spectra (PES) for both bulk and nanocrystal CeO2 have been measured on and off resonance of Ce 4d 4f absorption edge. The PES show that the bulk and nanocrystal CeO2 of diameter ranging from 8nm to 50nm exhibit a peak near Fermi edge with binding energy of about 1.8eV. The 1.8eVpeak shows a strong dependence on excitation energy, although it looks like the contribution of Ce3+ ion following the data reported in literatures. However, according to the results of resonance photoemission and X-ray absorption spectra at O 1s edge, this electronic structure may be associated to the intermediate state charge transfer effects.