Absolute external luminescence quantum efficiency of zinc oxide

We report on the measurement of the absolute external luminescence quantum efficiency of various ZnO samples using a miniature integrating sphere fitted into a cryostat. Even the absolute luminescence quantum efficiencies per spectral interval are directly accessible. Measurements have been carried out on high quality bulk samples and different commercially available ZnO powders from 8 K up to room temperature. Activated processes lead to an overall decrease in the efficiency with temperature. All efficiencies are considerably below unity, making the identification of the luminescence decay time with the radiative life time very questionable.