Abstract
Single crystalline MAl2O4 (M = Ca and Sr) persistent phosphors, which are nominally pure or additionally doped with Eu and Nd or Dy, respectively, were investigated for their recombination luminescence (RL) and microwave-induced changes in the RL at low temperatures. The analysis of the optically-detected electron paramagnetic resonance (EPR) spectra, recorded after ultraviolet excitation at 4.2 K, shows that intrinsic donor and acceptor centres are involved in the recombination process. Spectral dependent RL-EPR measurements on undoped CaAl2O4 (CAO) and SrAl2O4 (SAO) show that we deal with only one donor but at least two different acceptors. The g value of the donor is 1.99 in CAO and 1.97 in SAO; the g value of the acceptors is about 2.02. The donor–acceptor recombination energy is either emitted directly (undoped samples) or almost completely transferred to the rare-earth activators (doped samples). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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