RESONANT PHOTOEMISSION-STUDY OF CEO2

The 4f electronic state and the decay process of the photoexcited 4d(9 )4f(n+1) states in CeO2 are investigated by means of a resonant photoe mission technique in the Ce 4d-->4f photoabsorption region. Resonant e nhancement of the valence-band emission is clearly observed in the gia nt-absorption region. This confirms the existence of the 4f electron i n the ground state of CeO2. The 4f-derived emission exhibits a single- peak distribution rather than a double-peak structure such as observed in other Ce compounds. The Ce 5p emission band, which spreads over ab out 10 eV and consists of at least three or more fine structures, also shows the resonant enhancement in the giant-absorption region. In the prethreshold region, the Ce 5p fine structures as well as the 4f emis sion band show enhancements, but these constant-initial-state spectra are different from each other. The obtained results are discussed in t erms of the mixed valence in the ground state of CeO2 and of possible intermediate configurations in the resonant photoemission process.