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 p(z) 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 Y-89 superhyperfine structure to be Y3+ and conforms to the above model. The second has the most anisotropic g values yet observed in an oxygenic-hole centre in zircon. Two g values are significantly below the free-electron value and a p(x) ground state is inferred.