Kinetics of luminescence decay in electron-irradiated sapphire crystals

The kinetics of luminescence decay in electron-irradiated sapphire (alpha-Al2O3) single crystals have been investigated using time-resolved luminescence spectroscopy. The data, observed over timescales from tens of nanoseconds to tens of milliseconds, characteristically feature a rapid decay of intensity punctuated by discrete plateau regions. Simple theoretical models, invoking such theories as first- or second-order mechanisms, rate laws or power-law dependences, are unable to explain these features. A theoretical model comprising bimolecular electron-hole recombination, together with unimolecular electron detrapping from two discrete traps, qualitatively accounts for these features.