Aggregation processes in LiF:Mg2+

Static defect simulations were performed in LiF:Mg2+ for calculating formation, binding and activation energies of dipolar defects. Another type of dipole configuration is proposed that differs from the well known impurity-vacancy dipole (I-V) in alkali halides. Instead of a cation vacancy near the divalent impurity, an interstitial fluorine occupies the center of the cube forming an impurity-interstitial dipole (I-I). The value of the calculated activation energy, 0.661eV, agrees quite well with the one obtained by McKeever and Lilley for the I-V dipole. In this paper, the calculated activation energy for the I-V dipole is 0.864eV. The two values are near enough to consider a possible coexistence of both. The calculated energies indicate that three dipoles form a trimer without the occurence of an intermediary dimer. The same behaviour is also observed for CaF2.