The angular dependence and Zeeman splitting of optically detected nuclear magnetic resonance (ODNMR) spectra of the ${}_{}{}^7{}_{}{}^{}\mathrm{F}_0^{}{}_{}{}^{}$ ground state of ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}_{}^{3+}{}_{}{}^{}$ in ${\mathrm{LaF}}_3$ have been measured in optical-rf double resonance experiments. Splitting of the degeneracy-left ODNMR spectrum is attributed to magnetically inequivalent ${\mathrm{Eu}}^{3+}$ sites. In analysis of the magnetic-field angle dependence of the spectra with an effective-operator Hamiltonian, nuclear quadrupole and magnetic interaction parameters as well as the orientation of the principal axes are determined. None of the principal axes coincides with the crystallographic axes. But the directions of the magnetic interaction tensors for different ${\mathrm{Eu}}^{3+}$ sites relate to each other according to a ${\mathit{C}}_2$ symmetry. © 1996 The American Physical Society.

• Received 21 December 1995

DOI:https://doi.org/10.1103/PhysRevB.54.483