Far-Infrared Spectra of Erbium, Dysprosium, and Samarium Ethyl Sulphate

A far-infrared interferometric spectrometer has been used to make the first direct observation of transitions between the Stark- and Zeeman-split ground J manifolds of rare-earth ions in ethyl sulphate crystals. The description of both the Stark and Zeeman splittings in terms of crystal-field theory has been considered, and the data obtained here have proved sufficient for making an accurate evaluation of the parameters contained in the theory. The intensities of the observed transitions have been investigated and it has been found that they are primarily magnetic-dipole transitions. However, significant deviations between calculation and observation occurred for both the splittings and line intensities. A hypothesis has been developed by which both kinds of discrepancies are attributed to interaction between the rare-earth-ion electronic states and the phonons or lattice waves in the ethyl sulphate crystals.