Measurements of the infrared transmission spectra up to similar to 10 000 c
m(-1), ab-initio calculations based on the density functional theory and th
e use of an anisotropic exchange Hamiltonian to describe the magnetic coupl
ing of rare earth (RE)-Cu are new instruments shown in this paper to provid
e an additional insight into the nature of the 4f splitting in rare earth (
RE) cuprates. (i) Sets of the parameters of the crystal field Hamiltonian f
or trivalent Nd and Sm in regular as well as in Ba-sites in RE1+xBa2-xCu3O6
+y are determined; (ii) Nd2CuO4 is found to be an exceptionally suitable sy
stem to study the anisotropy of the exchange interaction: Kramers doublet s
plittings due to the superexchange Cu-Nd interaction, deduced from the inte
rmultiplet transitions spectra, are interpreted in terms of an effective Ha
miltonian for the Nd3+ ion expressed in terms of single electron spherical
tensor operators up to the sixth order; (iii) it is shown that the defects
in Nd2CuO4, Nd2-xGdxCuO4 and Nd2-xCexCuO4, that give rise to satellites in
the spectra of 4f excitations, are universal and related to a local lattice
deformation associated with a charge inhomogeneity. (C) 2001 Elsevier Scie
nce B.V. All rights reserved.