Theory of Zeeman Effect for Rare-Earth Ions in Crystal Field with C3h Symmetry

Rare-earth ions in ethylsulfate crystals give rise to sharp-line optical absorption spectra. The purpose of this paper is to give a part of the theory of the Zeeman effect for these lines. Special cases considered especially are when the magnetic field is parallel or perpendicular to the c axis, when the light polarization is parallel or perpendicular to both the c axis and the magnetic field, and when the crystal is rotated about the c axis while the light polarization and magnetic-field directions are held constant. The dependence of the frequency and intensity of the lines on the crystal orientation gives a measure of certain properties of the internal crystal fields which have not been observable before.