ZnO film deposited on AlN shows excellent blue emission. Photoluminescence (PL) emission is further enhanced by annealed treatment. The corresponding emission mechanism is discussed. V-Al-O-N are the dominant form of V-Al in as grown AlN samples. When the energy of the incident photons is just enough to pump the electrons up to the V-Al-O-N energy level, a mass of electrons can be directly trapped by the V-Al-O-N defect centers, which will induce effective transitions from these defect energy level to the top of the valence band, and then transitions to Zn vacancies levels in ZnO due to similar lattice constants between ZnO and AlN. The energy interval between the V-Al-O-N in AlN and the Zn vacancies defect states in ZnO is about 2.96 eV, which is well consistent with the energy of the blue peak at 420 nm (2.96 eV). (C) 2017 Elsevier Ltd. All rights reserved.