N[O.sup.2-.sub.3] and C[O.sup.-.sub.2] centers in synthetic hydroxyapatite: features of the formation under γ- and UV-irradiations

The EPR studies of synthetic hydroxyapatite containing carbonate and nitrate ions exposed to γ - ray and UV irradiations have been performed. It has been found that γ irradiation leads to the formation of both [NO.sup.2-.sub.3] and [CO.sup.-.sub.2] paramagnetic centers, while the UV irradiation induces only [NO.sup.2-.sub.3] centers. To explain this fact, the hypothesis has been proposed, according to which in the hydroxyapatites studied, there coexist complexes consisting of nitrate ions and shallow electron traps that serve as sources of secondary electrons during UV irradiation. The EPR spectroscopy parameters (g and A) of the detected centers have been determined and compared with similar centers in hydroxyapatite with a different impurity composition. The study of the thermal stability of the centers has demonstrated that, in the temperature range 20-300°C, the [NO.sup.2-.sub.3] centers formed by UV irradiation are more stable than the same centers created by γ - ray irradiation.