Lattice-embedded multiconfigurational self-consistent-field calculations of the Mn-perturbed F-center defect in CaF2:Mn.

Abstract

We report on the results of ab initio ground- and excited-state multiconfigurational self-consistent-field (SCF) embedded-cluster calculations for the Mn-perturbed F-center (Mn/F) defect in ${\mathrm{CaF}}_{2}$:Mn. This defect has long played a central role in the understanding of the absorption and emission characteristics of this material following irradiation. An approximate embedding method is employed whereby the potential due to the external lattice surrounding the cluster representing the Mn/F defect is described by means of lattice-centered Gaussian charge distributions, the parameters of which are determined in conjunction with SCF 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 using the method of complete active space SCF. These calculations show that the ground state of the Mn/F defect is spin 2 thus making the optical transitions spin-allowed, and accounts for the absorption oscillator strength enhancement following irradiation. The calculated excited-state levels are used to interpret the observed optical absorption spectrum. Our calculations also show that the important peak at 540 nm does not arise from transitions within the Mn/F defect considered in this study. This peak is possibly related to Mn-perturbed M centers.