Abstract
Using time-resolved photoluminescence spectroscopy we have measured the lifetime of the F-center luminescence from α-Al2O3:C. The measurements reveal a lifetime of 35–36 ms at room temperature, decreasing to <2 ms over the temperature range from 370 to 500 K. The decrease in the lifetime is shown to follow a classical Mott-Seitz dependence for thermal quenching of luminescence, with an activation energy W of ∼1.08±0.03 eV and a corresponding frequency factor ν of ∼1014 s−1. Similar values for the energy and frequency factor were also obtained from an analysis of thermoluminescence (TL) glow curves measured at different heating rates, when the TL is measured over a wavelength range corresponding to the F-center luminescence emission (centered at 420 nm). Furthermore, the parameters obtained were independent of the glow curve shape, the degree of trap filling, or the specific conditions under which the crystals were grown. This is interpreted as a demonstration that the well-known heating rate dependence of the TL from this material is a result of thermal quenching of the F-center emission. Whereas the thermal quenching parameters obtained from measurement of the luminescence lifetime and from the heating rate analysis of the TL glow curves are independent of the sample type, the degree of trap filling, and the heating or cooling rate, measurements of the photoluminescence intensity, induced by absorption of F-band light, were found to be dependent upon all of the above conditions. This difference in behavior is attributed to a phosphorescence signal from traps associated with the ∼265, ∼310, and ∼450 K TL peaks.
Published Version
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