Defect models of the three trigonal Ti3+ centers in LiF:Ti3+ and LiF:Ti3+:Mg2+ crystals

The EPR g factors of the trigonal Ti3+ center A in LiF:Ti3+ and two additional trigonal Ti3+ centers B and C in LiF:Ti3+:Mg2+ crystals are calculated from the third-order perturbation formulas based on the cluster approach. From the calculations and by considering the Ti3+ displacement along 〈1 1 1〉 axis obtained by ENDOR experiment, the defect models for the three Ti3+ centers are suggested. For center A, there are two possible models: (i) [Ti3+F3−O32−] cluster and (ii) [Ti3+F6−] cluster with the Ti3+ off-center caused by a neighboring Li+ vacancy (VLi+) at 〈1 1 1〉 axis. The latter seems the more likely. The defect models of centers B and C are the [Ti3+F3−O32−] clusters associated with a neighboring: Mg2+ ion at the Li+ site along 〈1 1 1〉 axis in the vicinity of three F− ions and three O2− ions, respectively. The reasonableness of these models is discussed.