A measurement of the ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}_{}^{3+}{}_{}{}^{}$ ${}_{}{}^5{}_{}{}^{}\mathrm{D}_0^{}{}_{}{}^{}$ excited-state hyperfine splittings in the host crystal ${\mathrm{YAlO}}_3$ using an optical-rf nuclear double-resonance method, is combined with previously measured values of the quadrupole interaction in the ${}_{}{}^7{}_{}{}^{}\mathrm{F}_0^{}{}_{}{}^{}$ electronic states to obtain separately the lattice and the electronic contributions to the quadrupole coupling constant D. The ratio $D_{\mathrm{latt}/D_{4f}}$ is equal to -2.03 for ${}_{}{}^7{}_{}{}^{}\mathrm{F}_0^{}{}_{}{}^{}$ in the crystalline host ${\mathrm{YAlO}}_3$. For the ${}_{}{}^5{}_{}{}^{}\mathrm{D}_0^{}{}_{}{}^{}$ level, the ratio $D_{\mathrm{latt}/D_{4f}>30\mathrm{}}$..AE

• Received 19 February 1986

DOI:https://doi.org/10.1103/PhysRevB.34.36