Investigations of the electron paramagnetic resonance g factors for the two Er3+ centers in SrLaAlO4

The electron paramagnetic resonance (EPR) g factors for the tetragonal and rhombic Er3+ centers in SrLaAlO4 (SLA) are theoretically investigated by using the perturbation formulas of the g factors for a 4f11 ion in tetragonal and rhombic symmetries. In these formulas, the contributions to the g factors arising from the second-order perturbation terms and the admixture of various energy levels are included. The crystal-field parameters used in the calculations are determined from the superposition model and the structural data of the tetragonally and rhombically distorted [ErO9]15− clusters. Based on the studies, the rhombic center may be ascribed to the impurity Er3+ undergoing an off-center displacement ΔX (≈0.37 Å) along one of the [1 1 0] axes, due to the relaxation effect in the ab plane where one of its nine second-nearest-neighbor La3+ is substituted by an additional Er3+ at the high concentration. The calculated g factors for Er3+ on both Sr2+ and La3+ sites (particularly their average values) show reasonable agreement with the experimental data. This may be regarded as one theoretical indication of the compositional disorder of Sr2+ and La3+ in SLA, in addition to the line broadening of the experimental optical and EPR spectra. The contributions to the g factors from various effects are discussed.