Epr Spectra of Pairs of Interacting Rare-Earth Ions

The EPR spectra of interacting pairs of Dy3+, Tb3+, and Ho3+ ions in rare-earth ethyl sulfates have been studied in order to determine the nature and magnitude of the interactions. The departures from dipole–dipole interaction are mostly rather small, except for the interaction between a pair of Dy3+ ions, one of which is in the ground doublet and the other in the first excited doublet at 16 cm−1. A discussion is given of the difficulties of differentiating between the effects of electric quadrupole–quadrupole interaction and virtual phonon exchange interaction.