Vanhaelewyn, G. C. A. M., Morent, R. A., Callens, F. J. and Matthys, P. F. A. E. X- and Q-band Electron Paramagnetic Resonance of CO₂⁻ in Hydroxyapatite Single Crystals.

Both X- and Q-band electron paramagnetic resonance (EPR) research has been conducted using slightly carbonated hydroxyapatite (HAp) single crystals after exposure to ionizing radiation. Below a temperature of 90 K, O⁻ and CO₂⁻ radicals were detected, whereas at room temperature only CO₂⁻ spectra could be observed. The O⁻ ion has previously been investigated in high-purity HAp single crystals, whereas EPR spectra of CO₂⁻ in HAp single crystals have not been reported. Both paramagnetic defects exhibit EPR angular variations in planes containing the c axis of the crystal from which spin Hamiltonian parameters were derived. Arguments are given for the presence of two CO₂⁻ defects in the irradiated HAp single crystals.