Magnetic circular dichroism spectra of divalent lanthanide ions in calcium fluoride

The broad-band spectra of most of the divalent lanthanide ions in calcium fluoride were studied with circularly polarized light in magnetic fields at liquid-helium temperatures. Large field- and temperature-dependent anisotropies were found in the bands of ions having an odd number of electrons, all of whose states have Kramers degeneracy. A variety of effects are seen for ions having an even number of electrons, ranging from zero as in CaF2:Er2+ to the large, complex effects in CaF2:Dy2+. The magnetic linear dichroism (MLD) of both Dy2+ and Eu2+ were also measured. The magnetic circular dichroism. (MCD) effects of the photochromic ions La2+, Ce2+, Gd2+, and Tb2+ are similar to each other and are only briefly described. This study is primarily concerned with the nonphotochromic ions, whose spectra are due to transitions between the opposite-parity configurations 4f(n) and 4f(n-1) 5d. These ions all have the ground configuration 4f(n). The magnetic dichroism effects are discussed in terms of the symmetry properties of the lanthanide ion. The large magneto-optic effects are the result of large spin-orbit coupling and predominantly totally symmetric vibronic coupling. Since the MCD and MLD effects are large throughout entire bands, they may be conveniently used in a variety of optical pumping experiments and may serve to detect changes in level populations.