EPR and optical-absorption studies of Cmsup3+ inYPO4andLuPO4single crystals

${}_{}{}^{244}{}_{}{}^{}{\mathrm{Cm}}^{3+}$ has been incorporated as a dilute impurity in single crystals of the tetragonal-symmetry lanthanide orthophosphate hosts, ${\mathrm{LuPO}}_4$ and ${\mathrm{YPO}}_4$. EPR spectroscopic observations were made of all of the excited doublets in the ground ${}_{}{}^8{}_{}{}^{}\mathrm{S}_{7/2}^{}{}_{}{}^{}$ multiplet of ${\mathrm{Cm}}^{3+}$ in both host crystals. Excited-state resonances were observed at both 77 and 4.2 K by use of X-band frequencies. The observed axial g values were used to compute the admixed wave functions for all four doublet levels in the ground manifold of ${\mathrm{Cm}}^{3+}$ and to calculate the g value expected for the lowest-lying doublet that could not be observed by EPR spectroscopy. Optical-absorption and Zeeman-effect investigations were carried out for the case of ${\mathrm{Cm}}^{3+}$ in ${\mathrm{YPO}}_4$, and a ground-state g value was obtained for the lowest-lying doublet in the ground-state manifold that was in excellent agreement with the value predicted by use of EPR results for the three excited-doublet levels. The Mohr-circle construction was used to obtain additional information regarding the nature of the crystal-field interaction for ${\mathrm{Cm}}^{3+}$ in the two crystal systems. In particular, the tetragonal crystal-field interaction was found to be stronger in the ${\mathrm{YPO}}_4$ host than in ${\mathrm{LuPO}}_4$. Additionally, the crystal-field-induced admixtures were found to be smaller at 77 K than at 4.2 K for both hosts, and the signs of the Steven’s parameters were determined to be positive for $b_4^0$ and negative for $b_2^0$.