Theoretical studies of the g factors and local structure for Pt 3+ in α -Al 2 O 3

The anisotropic g factors and local structure for the trigonal Pt 3+ centre in α -Al 2 O 3 are theoretically investigated from the perturbation formulas of the g factors for a 5 d 7 ion in trigonal symmetry. The Pt 3+ 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 -Al 2 O 3 is theoretically clarified, and the possibility of Pt + (5 d 9 ) is thus excluded in this work.