Optical and ESR study ofEr3+inLiNbO3

We report laser-excited optical transitions between the ${}_{}{}^4{}_{}{}^{}$ ${\mathit{S}}_{3/2}$ and ${}_{}{}^4{}_{}{}^{}$ ${\mathit{I}}_{15/2}$ multiplets of ${\mathrm{Er}}^{3+}$ as an impurity in the ${\mathrm{LiNbO}}_3$ host, together with the optical-absorption spectra at liquid-helium and liquid-nitrogen temperatures. The optical data allow us to determine the crystal-field splittings of those levels and the spin-Hamiltonian parameters for the ${}_{}{}^4{}_{}{}^{}$ ${\mathit{I}}_{15/2}$ lower multiplet. The observed electron-spin resonance and the angular variation of this spectrum agree with the parameters obtained by optical techniques. Both techniques show that only one of the three possible trigonal sites in ${\mathrm{LiNbO}}_3$ is occupied by ${\mathrm{Er}}^{3+}$ within the experimental sensitivity, in agreement with recent x-ray standing-wave measurements.