Unstable luminescence in GaN and ZnO

We report observations of unstable photoluminescence (PL) in GaN and ZnO. Beginning with GaN, a broad blue band with a maximum at 3.02 eV and well-defined fine structure at its high-energy wing bleached under ultraviolet (UV) exposure at low temperatures. The bleaching of this band was accompanied by enhancement of a broad yellow band peaking at 2.2eV. We also observed a very similar PL evolution in undoped bulk ZnO samples, where the intensity of the green band (at 2.6eV) significantly decreased with concomitant enhancement of the yellow band (at 2.25eV). The transformations are explained by recombination-enhanced defect reactions in these materials. (c) 2005 Elsevier B.V. All rights reserved.