Interactions between cerium ions in rare earth ethyl sulphates

EPR measurements have been made of Ce nearest and second nearest neighbour pairs in europium, yttrium and lutecium ethyl sulphates. The information obtained from these measurements has been used, in conjunction with previous data on pure cerium ethyl sulphate, to obtain the elements of the interaction tensors. This sheds new light upon the interaction mechanisms. It is shown that the large nondipolar interaction cannot be due to exchange or electric quadrupole-quadrupole interactions alone, but is due mainly to virtual phonon exchange, with interaction parameters more than an order of magnitude larger than those hitherto calculated using a simple Debye model for the phonon spectrum and orbit- lattice coupling parameters estimated from the static crystal field.