Ma. Perrin et E. Wimmer, COLOR OF PURE AND ALKALI-DOPED CERIUM SULFIDE - A LOCAL-DENSITY-FUNCTIONAL STUDY, Physical review. B, Condensed matter, 54(4), 1996, pp. 2428-2435
The electronic structure and mechanisms for the optical excitations of
pure and Na-doped gamma-Cep(2)S(3) have been investigated using first
-principles local-density-functional theory. The energy-band structure
s from augmented spherical-wave calculations indicate that the S 3p-->
Ce 5d interband transitions give rise to absorptions in the ultraviole
t, whereas the observed led color of gamma-Ce2S3 is associated with lo
calized Ce 4f-->5d excitations. The cationic vacancies in gamma-Ce2S3
(which is derived from th cubic Th3P4 structure) lead to the formation
of vacancy bands, which are split off from the top of the S 3p valenc
e band. Na doping removes these vacancy bands and homogenizes the band
edges of the valence and conduction bands. As a consequence, the onse
t of the f-->d transitions is shifted slightly to larger energies and
becomes sharper, which is consistent with an observed change in the co
lor of gamma-Ce2S3 from maroon to red-orange upon doping with Na.