Zeeman Effect in the $4f\to 5d$ Spectrum of ${\mathrm{Ce}}^{3+}$ in Ca${\mathrm{F}}_2$

The Zeeman effect of the ${\mathrm{Ce}}^{3+}$ ion with tetragonal charge compensation in Ca${\mathrm{F}}_2$ has been studied at 4.2°K. An absorption line at 3131.6 Å has been split with fields of 60 kG, and although all the components cannot be resolved, there is good agreement with epr results for the ground state. Axial stress results identify the upper state as having crystal quantum number $\mu =\pm \frac{1}{2}$. The occurrence of $4f^n\to 4f^{n-1\mathrm{}}5d$ spectra in the trivalent rare earths is discussed. In an appendix, a result is established concerning the use of the Zeeman effect to identify the $\mu =\pm \frac{1}{2}$ and $\mu =\pm \frac{3}{2}$ components of a cubic ${\Gamma }_8$ level split by a tetragonal distortion.