Reprinted with permission from Ning, L., Wu, C.,Li, L., Lin,L., Duan, C., Zhang, Y. and Luis Seijo. "Theoretical study on structural properties and 4f 5d transitions of locally charge-compensated Ce3+ in CaF2". The Journal of Physical Chemistry C 116.34 (2012): 18419-18426.The structural properties and 4f → 5d transitions of
Ce3+ in CaF2, with local charge compensation by an interstitial fluoride
(Fi
′) or an oxygen substitution for fluoride (OF′), have been studied
using the density functional theory (DFT) within the supercell model
and the wave function-based embedded cluster calculations,
respectively. The DFT results indicate that the incorporation of locally
charge-compensated Ce3+ in CaF2 induces an anisotropic distortion of
the structure around the dopant site. On the basis of the DFToptimized
structures, the Ce-centered embedded clusters are
constructed, on which the wave function-based CASSCF/CASPT2/
RASSI−SO calculations at the spin−orbit level are performed to obtain
the Ce3+ 4f1 and 5d1 level energies. The calculated 4f−5d transition
energies and relative intensities are in good agreement with available
experimental results. From the present calculations, we conclude that the 5d1 level missing in the low-temperature absorption
spectrum of the tetragonal Ce center with Fi
′ compensation is the second-lowest one, and the absorption at this level is
overshadowed by an adjacent cluster band usually assigned to Ce clusters and thus was not observed in experiments. We also
assign the two closely spaced absorption lines around 3118.5 Å observed in experiments to the lowest two quasi-degenerated 4f
→ 5d transitions of the monoclinic center with Fi
′ compensation rather than those of the trigonal center as proposed earlier.
Finally, we analyze the structural and electronic reasons for the large reduction (∼2000 cm−1
) of the lowest 4f → 5d transition
energy from a Fi
′ to a nearest-neighbor OF′ compensation, in terms of the changes in the centroid energy difference and crystal-
field splittingThis work was supported by the NSFC (Grants 11174005,
11074315, 90922022, and 10804001) and the Program for
Innovative Research Teams in Anhui Normal University of
China. L.S. acknowledges support from MEC-Spain (Grant
MAT2011-24586
