The role of defect states in the creation of intrinsic (WO4)3-centers in PbWO4 by sub-bandgap excitation

Intrinsic (WO4)(3-) centers can be created in lead tungstate by irradiation with light having energies well below the bandgap, i.e. the threshold for excitation of the blue tungstate luminescence. Detailed photo-ESR studies show that this happens by ionization of defect states in the bandgap which have been prefilled by suitable radiation. Depending on the energy depth of the respective defects a wavelength between near-infrared and near-UV is necessary for the ionization process. A simultaneous production of different electron centers is observed via participation of the conduction band. This allows an easy determination of the trap level energies. (C) 2001 Elsevier Science Ltd. All rights reserved.