The lifetime of the F-center luminescence from C-doped α-phase samples was measured by means of time-resolved photoluminescence spectroscopy. The measurements revealed a lifetime of 35 to 36ms at room temperature; decreasing to less than 2ms at temperatures ranging from 370 to 500K. The decrease in the lifetime was shown to obey a classical Mott-Seitz dependence for the thermal quenching of luminescence, with an activation energy of about 1.08eV and a frequency factor of 1014/s. Similar values for these parameters were also obtained by analyzing thermoluminescence glow curves which had been measured, at various heating rates, when the thermoluminescence was measured over a wavelength range which corresponded to an F-center luminescence emission which was centered at 420nm. The parameters which were obtained were independent of the glow-curve shape, the degree of trap-filling, and of the conditions under which the samples were grown. It was concluded that this demonstrated that the well-known heating-rate dependence of thermoluminescence from this material was a result of thermal quenching of the F-center emission. Whereas the thermal quenching parameters which were obtained from measurements of luminescence lifetime, and from a heating-rate analysis of the thermoluminescence glow curves were independent of the sample type, the degree of trap filling and the heating or cooling rate, measurements of the photoluminescence intensity, as induced by the absorption of F-band light, were found to be dependent upon all of those parameters. This difference in behavior was attributed to a phosphorescence signal from traps that were associated with the 265, 310 and -450K thermoluminescence peaks.

Thermal Quenching of F-Center Luminescence in Al2O3:C. M.S.Akselrod, N.A.Larsen, V.Whitley, S.W.S.McKeever: Journal of Applied Physics, 1998, 84[6], 3364-73