Thermoluminescence spectroscopy of Eu2+ and Mn2+ doped BaMgAl10O17

Thermoluminescence (TL) studies of Eu2+ and Mn2+ doped BaMgAl10O17 (BAM) are reported and discussed. The TL spectra that are measured after irradiation with ultraviolet (120-350 nm) show a series of TL peaks between 100 and 300 K. The TL spectra are similar for BAM with the two dopants, which suggest that the shallow traps are typical for the BAM host lattice. Using the Hoogstraaten analysis trap depths between 0.1 and 0.2 eV are determined. A model is proposed based on thermally activated recombination in local TL centres (not via the conduction band). Further support for this model is obtained from the observation that the TL signal is strongest for excitation around the band edge of BAM (similar to 180 nm). Upon heating the samples in air all low temperature TL peaks decrease in intensity. In addition a new peak appears in the TL spectrum, which is connected with a deeper trap (0.3 eV) and also a partial oxidation of Eu2+ to Eu3+ is observed. The luminescence efficiency is lower and the UV induced degradation is faster after annealing in air. These results indicate that the shallow traps are related to oxygen vacancies. The shallow traps do not have a negative influence on performance (efficiency and degradation) of BAM as a lighting phosphor. The luminescence efficiency and stability are strongly influenced by the formation of Eu3+ and a deeper trap during annealing in air. Subsequent annealing in a reducing atmosphere restores the original properties. (C) 2002 Elsevier Science B.V. All rights reserved.