Gw. Burdick et al., Ambiguities in the parametrization of 4f(N)-4f(N) electric-dipole transition intensities, PHYS REV B, 59(12), 1999, pp. R7789-R7792
For most symmetries the standard parametrization of one-photon electric-dip
ole transitions between crystal-field levels of the 4f(N) configuration of
lanthanide ions produces identical intensities for several quite different
parameter sets. An alternative scheme makes this multiplicity transparent a
s independent sign choices for each subset of parameters corresponding to d
istinct polarizations. In addition, the alternative parametrization allows
separate fits to data for different polarizations. [S0163-1829(99)51212-5].