In contrast to the simple exponential decay of the luminescence lifetime of the R lines observed from stressed and unstressed single crystals, the luminescence decay from polycrystalline alumina, formed by the oxidation of a ferritic FeCrAlY alloy, is found to fit a stretched exponential. A stretch exponential is found to fit all the luminescence decays in the polycrystalline alumina and the dependence of the stretch parameters under biaxial residual stress and under uniaxial stress is reported. The mean lifetime varies linearly with the residual stress, as monitored by the R2-line shift. Using established piezospectroscopic relations, the stress dependence of the lifetime is found to be one-third of the hydrostatic pressure under uniaxial stress and two thirds under biaxial stresses. In contrast, the stretch exponent doesnt vary with stress.