Abstract
In cerium dioxide (CeO
2
) as semiconductor compound, the tuning of band gap energy is a pivotal feature for visible light applications. In this report, nanoparticles (NPs) of Ce
1 − x
Ni
x
O
2
(0.0 ≤ x ≤ 0.10) were synthesized through co-precipitation route. The structural, electronic state and optical band gap were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, Raman scattering and UV–Vis spectroscopy. XRD results revealed the single-phase nanocrystalline behavior of CeO
2
with cubic fluorite structure. The electronic configuration of the samples, probed via NEXAFS spectra at Ce M
5, 4
edges, demonstrated that the cerium exists in Ce
4+
and Ce
3+
mixed valence states. The formation of Ce
3+
ions in the vicinity of oxygen vacancies (
Ov
) were assessed also via Raman scattering and XANES spectra at Ce L
3
edge. The estimated concentrations of Ce
3+
were increased from 6 to 13% as the Ni content increase from 0 to 10% respectively. Here, the inclusion of Ni
2+
ions into CeO
2
network induced additional
Ov
and simultaneously reduced the optical band gap from 3.9 eV for pure CeO
2
to 2.6 eV for 10% Ni doped CeO
2
NPs. Therefore, the oxygen loss population seem to be responsible for the band gap reduction. The role of
Ov
for creating profound donor band near the conduction band and narrowing the band gap energy were discussed.