The vibrations of PO4−3 ions in single crystals of hexagonal Ca10(PO4)6F2 have been observed by means of polarized Raman scattering and polarized infrared reflectance. The T2(ν3) and T2(ν4) Raman vibration frequencies are each observed to split in accord with the predictions of the factor group of the unit cell. The optically active vibrational modes are also observed, and the anisotropy of the extraordinary ray frequencies have been measured. The observations are analyzed in terms of dipole–dipole interionic forces using Ewald dipole summation techniques to account for the entire phosphate lattice. Qualitative agreement between the dipole model and experiment is achieved. The roles of short-range forces and background dielectric shielding are discussed.

The x-ray coloration of synthetic calcium fluorophosphate (fluorapatite) crystals is shown to result from the presence of fluorine vacancy defects. Three of these defects have been studied by correlating their optical absorption bands with their electron-paramagnetic-resonance spectra, and by application of the electron-nuclear-double-resonance technique to measure the F 19 and P 31 hyperfine interactions. The models proposed for these three axially symmetric defects consist of an electron trapped at (a) an isolated F~ ion vacancy, (b) a F~ ion divacancy associated with a charge-compensating 0 = ion, and (c) a second configuration of defect (b). Several paramagnetic hole-excess centers are also described. No optical absorption bands between 0.3 and 1.5 n have been observed for the hole centers.

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Articles you may be interested inVibrational quenching of excitonic splittings in H-bonded molecular dimers: The electronic Davydov splittings cannot match experiment

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