Electron paramagnetic resonance studies on the defects formed in the Dy(III)-doped SrAl2O4

EPR and photo-EPR investigations have been carried out for the SrchiAl2O4 with a variety of x and the SrAl2O4:Dy in relevant to elucidate the mechanisms of long phosphorescence of SrAl2O4:Eu,Dy. When the SrchiAl2O4 and SrAl2O4:Dy were irradiated by UV-light, they showed the EPR spectra with eleven hyperfine lines independent of dysprosium(III)-doping. Taking into account of the SrAl2O4 framework consisting of tetrahedral AlO4- network and of aluminium nuclear spin I-Al = 5/2, they were assigned to [AIO(4)(0)], indicating that the reaction AIO(4)(-) --> AIO(4)(0) + e(-) occurs by UV-irradiation. Also, an anisotropic resonance with a g value of 2.007 at the cross-over point was observed for the SrAl2O4:Dy in addition to the hyperfine lines. From the comparison of the decay characteristics of both EPR signals it is deduced that the anisotropic signal is due to a trapped hole in the SrAl2O4, which plays an important role in long phosphorescence of the SrAl2O4:Eu,Dy. (C) 2004 Elsevier SAS. All rights reserved.