, introducing an additional electronic level by
doping praseodymium. The 4f valence shell of Ce4+([Xe]) in
cerianite is empty, and that of O2 ([Ne] 2s2 2p6) is full: adjacent
Ce4+ ions are virtually in contact in the fluorite lattice and, as a
result, 4f orbitals overlap in a cationic conduction band;
similarly, overlap of 2p orbitals of oxygen ions gives to an
anionic valence band. The Ce–O bonds have a stronger ionic
character, and hence a smaller contribution of the Ce 5d and 4f
orbitals in the VB, in CeO2 [25]. The band gap between the
anionic band and the cationic band is 3.01 eV. By doping CeO2
with Pr4+ ions, the 4f1 electron of the praseodymium valence