First-principles ground-state and excited-state multi-configurational self-consistent field embedded-cluster calculations were made of Mn-perturbed F-centers (Mn/F defect) in Mn-doped material. It was recalled that this defect had long played a central role in the understanding of the absorption and emission characteristics of the present material after irradiation. An approximate embedding method was used in which the potential that was due to the external lattice surrounding the cluster which represented the Mn/F defect was described by means of lattice-centered Gaussian charge distributions. The parameters for the latter were determined, in conjunction with self-consistent field force calculations, so as to stabilize the cluster. The ground and excited many-electron state energies, of spin 2 and 3, of the Mn/F defect were calculated by using the method of complete active space self-consistent fields. These calculations showed that the ground state of the Mn/F defect was spin 2, thus making the optical transitions spin-allowed, and accounted for the absorption oscillator strength enhancement which followed irradiation. The calculated excited-state levels were used to explain the observed optical absorption spectra. The calculations also showed that a marked peak at 540nm did not arise from transitions within the Mn/F defect that was considered in this study. It was instead suggested that the peak was perhaps related to Mn-perturbed M centers.

A.C.Lewandowski, T.M.Wilson: Physical Review B, 1995, 52[1], 100-9