Modeling the crystal-field splitting of the energy levels ofEr3+in charge-compensated sites in lithium niobate

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Abstract
We have calculated the crystal-field splitting of the energy levels of Er3+(4f11) in charge-compensated sites having C3 symmetry in the host crystal of lithium niobate, LiNbO3 (LN), with crystal-field parameters obtained from lattice-sum calculations. The charge-compensation model assumes that Er3+ substitutes into Li+ sites that are shifted from the 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+1LJ including the ground state 4I15/2 of Er3+(4f11) 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 Er3+ as C3, in agreement with magnetic resonance studies. The calculation also predicts the symmetry label of the ground-state Stark level as 2Γ6 or μ(±3/2), in agreement with the observed polarized absorption and fluorescence spectra.