Study of the effects of hydroxyapatite nanocrystal codoping by pulsed electron paramagnetic resonance methods

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 $\pm$ 15 nm during “wet” synthesis by CO$_{3}^{2-}$ carbonate anions and Mn$^{2+}$ cations on relaxation characteristics (for the times of electron spin–spin relaxation) of the NO$_{3}^{2-}$ nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion–cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.