  Given growing interest in optical-frequency magnetic dipole transitions, we
use intermediate coupling calculations to identify strong magnetic dipole
emission lines that are well suited for experimental study. The energy levels
for all trivalent lanthanide ions in the 4fn configuration are calculated using
a detailed free ion Hamiltonian, including electrostatic and spin-orbit terms
as well as two-body, three-body, spin-spin, spin-other-orbit, and
electrostatically correlated spin-orbit interactions. These free ion energy
levels and eigenstates are then used to calculate the oscillator strengths for
all ground-state magnetic dipole absorption lines and the spontaneous emission
rates for all magnetic dipole emission lines including transitions between
excited states. A large number of strong magnetic dipole transitions are
predicted throughout the visible and near-infrared spectrum, including many at
longer wavelengths that would be ideal for experimental investigation of
magnetic light-matter interactions with optical metamaterials and plasmonic
antennas.
