Luminescence of theFcenter in sapphire

Abstract
An F-center emission band (3 eV) has been observed in subtractively colored Al2 O3 crystals upon exciting with F light (6.1 eV). The lifetime of the 3 eV luminescence is 36 ± 4 msec. We attribute this long lifetime to the forbidden triplet-to-singlet transition of the F center. The FF+ conversion can be shown by studying the F and F+ emission bands in these crystals.