Oxygenic-hole centres in x-irradiated zircon: 10 K EPR studies

A surprisingly large number of paramagnetic hole centres in zircon have been observed and characterized by EPR. The field is reviewed and a model proposed based on some ten precisely measured centres. EPR data suggest that the trapped hole, produced by x-irradiation, is normally located in the non-bonding pz orbital of an O-ion and is stabilized by a nearby impurity cation, often, but not always, a +3 ion. Two previously unobserved oxygenic-hole centres are here reported. In one the stabilizing ion is shown from observed 89 Y superhyperfine structure to be Y3+and conforms to the above model. The second has the most anisotropic gvalues yet observed in an oxygenic-hole centre in zircon. Two gvalues are significantly below the free-electron value and a px ground state is inferred.