Interaction matrix determinations, including 17Al hyperfine and nuclear electric quadrupole matrices, were reported for an Al center. The latter had an electron which was removed from an adjacent O atom, and was referred to as an O-hole center. It was found in X-irradiated zircon by means of 8.9GHz electron paramagnetic resonance measurements at about 10K. Each of the parameter interaction matrices exhibited monoclinic symmetry, indicating sites of Laue class 2/m for both the hole-center and the interacting 27Al nucleus. Comparison with earlier results for 2 single electron-hole centers in zircon, and with the results for a similar center in  quartz, showed that the hole-center was trapped at a short bonded ligand O in the zircon structure, and interacted with an Al nucleus which replaced Si at an adjacent site. Each of the O and Si sites of the zircon structure had the point group symmetry, m.

R.F.C.Claridge, K.M.Mackle, G.L.A.Sutton, W.C.Tennant: Journal of Physics - Condensed Matter, 1994, 6[47], 10415-22