Ion migration energies and color center absorption in hydroxyapatite

By modelling a hydroxyapatite crystal lattice as a finite cluster of atoms surrounded by an array of point ions, molecular orbital MS-Xalpha calculations point to differences in fluoride and hydroxyl migration energies. Despite the fluoride ion being more tightly bound to the lattice, it is in fact more mobile. Color center optical absorption is predicted to be in the infrared region of the spectrum for hydroxyapatite, whereas for fluorapatite the absorption peak of a vacancy is predicted to within 2% of the observed peak in the optical region. This result is discussed in terms of experimental studies of bonding between the calcified and organic phases of bone.