Abstract
Gamma-irradiated chlorapatite, synthesized from a CaCl2 fl ux, has been investigated by powder and single-crystal electron paramagnetic resonance (EPR) spectroscopy at X- and W-band frequencies, including in situ high-T X-band EPR. The powder EPR spectra, particularly high-T X-band spectra and high-resolution W-band spectra, reveal a new hole-like center, H(III), in addition to two previously reported hole-like centers, H(I) and H(II). Center H(III) is characterized by an electron spin ½ and hyperfi ne interaction with one 35 Cl nucleus, suggesting a structural model consisting of a hole trapped by a substitutional oxygen ion adjacent to a Cl – ion vacancy in the anion column. This discovery of center H(III) also lends support to the structural model already proposed by other authors for center H(II). Single-crystal X-band EPR spectra also disclose a new electronic center, E(I). The structure model for center E(I) includes an electron trapped at an isolated Cl – ion vacancy in the anion column, corresponding to center F E(II) in fl uorapatite and similar to the well-known F center in alkali halides.
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