Hyperfine structure and nuclear and electronic Zeeman effect of theD21↔H43transition ofPr3+:CaF2

The electronic and nuclear magnetic moments and the effective nuclear-quadrupole interactions of the ground and excited states of the 2940.97-Å ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\leftrightarrow {}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ transition of ${\mathrm{Pr}}^{3+}$ ions in tetragonal sites of Ca${\mathrm{F}}_2$ have been measured using spectral hole burning, rf- and microwave-optical double-resonance and laser-excited fluorescence-excitation spectroscopy. The ground state is an electronic doublet of $E$ symmetry whose electronic magnetic moment tensor is given by $\frac{g_{\parallel }\beta }{h}=5.44\mathrm{}$ MHz/G and $g_{\perp }=0\mathrm{}$. The nuclear magnetic splitting factor parallel to the $C_4$ axis is $\frac{{\gamma }_{\parallel }^g}{2\pi }=1.65\mathrm{}$ kHz/G, and the effective quadrupole coupling constant $D^g=+1.39\mathrm{}$ MHz is dominated by pseudoquadrupole effects. The excited state is an electronic singlet, and rf-optical double resonance was used to determine the nuclear Zeeman splittings and obtain a very precise value for the nuclear magnetic moment of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$, i.e., $4.2754\left(5\right)\mathrm{}{\mu }_N$. For fields parallel to the $C_4$ axis, ${\gamma }^e$ is unenhanced: $\frac{{\gamma }_{\parallel }^e}{2\pi }=1.2924\mathrm{}\pm 0.0001$ kHz/G. However, $\frac{{\gamma }_{\perp }^e}{2\pi }=2.12\mathrm{}\pm 0.05$ kHz/G shows modest enhancement due to second-order admixture of other ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ electronic levels. This result is used to assign the symmetry of the excited state as $A_1$ in the point group $C_{4v}$, and to locate the $E \mathrm{level}\sim 200$ ${\mathrm{cm}}^{-1\mathrm{}}$ higher. Unlike that of the ground state, the excited-state quadrupole coupling is dominated by real electric quadrupole interactions, and the constant is determined to be $D^e=-0.44\mathrm{}$ MHz.