NMR Measurement of the Hyperfine Constant of an Excited State of an Impurity Ion in a Solid

An optically detected NMR measurement of the hyperfine tensor for an excited state of an impurity rare-earth ion (${\mathrm{Pr}}^{3+}$) in a solid (LiY${\mathrm{F}}_4$) is reported. The results have been used to obtain for the first time a measured value of the hyperfine interaction constant $A_j=616\mathrm{}\pm 51$ MHz of the ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ excited state. This is somewhat smaller than the calculated value of 754 MHz.