Electron Paramagnetic Resonance and Optical Zeeman Spectra of Type II CaF2:Er3+

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Abstract
A study was made of the EPR and optical spectra of trivalent erbium in Type II crystals of calcium fluoride. The EPR spectrum disclosed the existence of cubic, tetragonal, and trigonal sites in the approximate ratios 15:20:1. The splitting values agreed with those of Ranon and Low. The optical spectrum consisted predominantly of lines due to 〈100〉 tetragonal sites. This was established by a study of the Zeeman pattern of the lines as a function of rotation about the [1̄10] axis of the crystal. Spectra were taken over a range of 180° in increments of 5° in azimuthal angle. This provided a plot of energy versus azimuthal angle which could be used to establish the site symmetry in a purely geometric fashion. This technique is of general applicability to problems of nonequivalent sites and provides considerably more information than Zeeman studies restricted to a few crystallographic directions. Spectral lines too weak to be followed in a rotational Zeeman study were assigned by finding ground-state splitting factors associated with their Zeeman patterns or by locating corresponding transitions from excited states of the ground Stark manifold. For a number of lines, splitting factors were found and by consideration of the polarization of the Zeeman lines and the rotational Zeeman patterns, assignments of representations and crystal quantum numbers were made.