Point defects have been produced by electron irradiation in single-crystal α-${\mathrm{Al}}_2$${\mathrm{O}}_3$ from two different sources. Time-resolved luminescence spectroscopy has been used to study emission spectra and atomic-displacement thresholds for the defects. An emission band at 3.8 eV is present in only one of the crystals while a band at 4.2 eV is observed in both crystals. The former is probably due to ${\mathit{F}}^{+}$-center emission and the latter possibly arises from an F-center transition. Emission kinetics are consistent with detrapping of electrons from two shallow traps.

• Received 16 July 1992

DOI:https://doi.org/10.1103/PhysRevB.47.55