Magnetic-Susceptibility, Optical-Absorption, and Crystal-Field Energies for SrCl2:Yb3+

Magnetic-susceptibility measurements have been used to locate the low-lying crystal-field levels of Sr${\mathrm{Cl}}_2$:${\mathrm{Yb}}^{3+}$. The two upper levels arising from the crystal-field-split ${}_{}{}^2{}_{}{}^{}F_{\frac{5}{2}}^{}{}_{}{}^{}$ manifold were located by optical-absorption spectra. The five crystal-field levels were found to lie at 0, 155, 650, 10 193, and 10 612 ${\mathrm{cm}}^{-1\mathrm{}}$. A theoretical analysis showed that the magnetic-susceptibility, optical-absorption, and electron-spin-resonance data could not be correlated without the use of second-order crystal-field mixing. In spite of the reasonably good correlation among the three experiments, the analysis, which was based on an electrostatic model, did give some unexpected results for some of the more important physical quantities. This may indicate the importance of covalency and overlap in this crystal system similar to that already found for Ca${\mathrm{F}}_2$:${\mathrm{Tm}}^{2+}$.