EPR and Spin–Lattice Relaxation of Mo3+ Ions in Corundum

The EPR spectra of Mo3+ ions in corundum at v = 9.25 GHz and T = 77 °K were investigated. It is shown, that Mo3+ ions isomorphously replace Al3+ ions in the octahedral coordination. Due to the large zero‐field splitting, only the −1/2 ↔ +1/2 transition is observed. The zero‐field splitting constant 2D = (−49 ± 18) GHz, the spectroscopic splitting factor g⊥ = 1.968 ± 0.001, g ⊥ = 1.98 ± 0.01, and the hyperfine splitting constant A‖ = (119 ± 1) MHz, A⊥ = (121 ± 2) MHz are determined. It is shown that in the case of large zero‐field splitting 2D ≫ v the magnitude of 2D can be determined by measurements at a single frequency, using the value of geff at 35°2′ (cos2 θ = 2/3). The angular dependence of the hyperfine structure splitting due to the large zero‐field splitting is observed and good agreement with values calculated in first order of perturbation theory is obtained. The spin‐lattice relaxation times of Mo3+ ions in corundum are estimated from the magnitude of the broadening of the absorption curves with increasing temperature. In the temperature range of 77 to 500 °K the spin–lattice relaxation rate is τ1−1 ∼ T2.5.