The blue phosphor of BaMgAl10O17:Eu2+ (BAM) powders were prepared by solid-state reaction. The thermal degradation of BAM phosphor significantly reduces the intensity of the blue emission. BAM is reduced by an amount of 50% after heating at around 800degreesC for 1 h. Photoluminescence (PL) excitation and emission spectra showed that the blue emission of 450 nm peak decreased with increasing annealing temperature. The D-5(0) --> F-7(1) and D-5(0) --> F-7(2) transition of Eu3+ Were observed at 590 and 615 nm emission lines over 1100degreesC. Electron paramagnetic resonance (EPR) spectrum also detected two signals of Eu2+ corresponding to g = 3.7156(9) for 88mT, and g = 2.9507(9) for 133 mT. X-ray absorption near edge structure (XANES) spectrum decreased the intensity of Eu2+ for 6977 eV with increasing annealing temperature, while high-energy peak of Eu3+ for 6984 eV was increased. The combined use of X-ray and neutron data by the Rietveld refinement appears to support that the secondary phase of EuMgAl11O19 magnetoplumbite structure in BAM may be formed by heat treatment. (C) 2003 Elsevier Science B.V. All rights reserved.