We have calculated the crystal-field splitting of the energy levels of ${\mathrm{Er}}^{3+}{(4f}^{11})$ in charge-compensated sites having $C_3$ symmetry in the host crystal of lithium niobate, ${\mathrm{LiNbO}}_3$ (LN), with crystal-field parameters obtained from lattice-sum calculations. The charge-compensation model assumes that ${\mathrm{Er}}^{3+}$ substitutes into ${\mathrm{Li}}^{+}$ sites that are shifted from the ${\mathrm{Li}}^{+}$ positions in the undoped lattice with excess charge compensated for by niobium vacancies and defect complexes. The calculated splitting of 11 multiplet manifolds ${}^{2S+1}{L}_J$ including the ground state ${}^4{I}_{15/2}$ of ${\mathrm{Er}}^{3+}{(4f}^{11})$ is compared with existing data in the literature, as well as with polarized absorption and fluorescence spectra obtained in the present study between 8 K and room temperature. The calculated splitting is compared with the experimental splitting without least-squares adjustments to the crystal-field splitting parameters, although the centroids between multiplet manifolds are adjusted to account for J mixing between states. The calculated splitting supports site symmetries for ${\mathrm{Er}}^{3+}$ as $C_3,$ in agreement with magnetic resonance studies. The calculation also predicts the symmetry label of the ground-state Stark level as ${}^2{\Gamma }_6$ or μ(±3/2), in agreement with the observed polarized absorption and fluorescence spectra.

• Received 17 December 2003

DOI:https://doi.org/10.1103/PhysRevB.69.195103