Electronic Spectrum and Energy Levels ofGd3+in LaF3

The optical-absorption and fluorescence spectra of ${\mathrm{Gd}}^{3+}$ in crystals of La${\mathrm{F}}_3$, pure Gd${\mathrm{F}}_3$, and mixed crystals of 50% Ca${\mathrm{F}}_2$: 50% Gd${\mathrm{F}}_3$ are given. Absorption has been observed in all the states of the ${}_{}{}^6{}_{}{}^{}P$, ${}_{}{}^6{}_{}{}^{}I$, and ${}_{}{}^6{}_{}{}^{}D$ multiplets, with the exception of ${}_{}{}^6{}_{}{}^{}D_{\frac{1}{2}}^{}{}_{}{}^{}$ state. Fluorescence from the components of the ${}_{}{}^6{}_{}{}^{}P_{\frac{7}{2}}^{}{}_{}{}^{}$ state has been observed. A least-squares fit of 14 barycenters, with the inclusion of configuration interactions, gave a mean error of 43 ${\mathrm{cm}}^{-1\mathrm{}}$ between the calculated and experimental barycenters, with the parameter values $F_2=419.1\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $F_4=56.54\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $F_6=6.006\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, ${\zeta }_{4f}=1486\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and $\alpha =21.78\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. With the inclusion of spin-other-orbit and spin-spin effects, the mean error was reduced to 32 ${\mathrm{cm}}^{-1\mathrm{}}$. The intermediate-coupling free-ion calculation was carried out assuming nonhydrogenic ratios of the Slater parameters.