Paramagnetic Resonance and Optical Absorption in Gamma‐Ray Irradiated Alpha Quartz: The “Al” Center

The optical absorption spectra between 1.0 and 8.5 eV and the electron paramagnetic resonance spectra at 10 GHz of a synthetic crystal of α‐quartz grown on a z plate were measured as a function of 60 Co γ‐ray irradiation and thermal treatment. After initial irradiation, an estimate of a lower limit for the concentration of centers contributing to the resolved optical bands gave N ≳10 16 cm ‐3 for each band. An estimate of the concentration of spins of each of the distinct paramagnetic species gave N <3×10 15 cm ‐3 with the exception of the “Al” center for which N ∼3×10 15 cm ‐3 . Thermal bleaching and re‐irradiation of the crystal showed that the defects with bands in the 1.0 to 6.5 eV region were independent of the defects with bands in the 5.5 to 8.5 eV region and that undetected precursor defect configurations were altered by heating to form those defects whose optical bands (5.5 to 8.5 eV) increased after the second irradiation. The only correlation observed between paramagnetic defects and defects producing optical absorption bands was between the “Al” center and a band at 8.45 eV; the correlation was quite weak.