The anisotropic 𝑔 factors and local structure for the trigonal Pt3+ centre in 𝛼-Al2O3 are theoretically investigated from the perturbation formulas of the 𝑔 factors for a $5d^7$ ion in trigonal symmetry. The Pt3+ impurity is found to experience an outward displacement by about 0.18 Å away from the centre of the oxygen octahedron along the $C_3$-axis. The calculated g factors based on the above axial displacement show good agreement with the observed values. Importantly, the pending problem of $+3$ valence state of the doped Pt in 𝛼-Al2O3 is theoretically clariﬁed, and the possibility of Pt+ ($5d^9$) is thus excluded in this work.
Volume 94, 2020
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