Photoluminescence of Eu2+-doped mullite (xAl2O3•ySiO2; x/y=3/2 and 2/1) prepared by a hydrothermal method

Mullite with different Al2O3/SiO2 ratios (3/2 and 2/1) is prepared by the decomposition of the precursor prepared by the hydrothermal method at above 1300 degrees C. The phase relations and thermal events during the decomposition are studied by powder X-ray diffraction and thermal analyses. Presence of defect centres is revealed by electron paramagnetic resonance (EPR) spectroscopy and are nonemissive. Eu2+-doped mullite shows blue luminescence and the luminescence characteristics show composition dependence. The emission maximum of Eu2+-doped 3/2-mullite is around 460 nm and that of Eu2+-doped 2/1-mullite is around 420 nm. Shift in the emission maxima with change in the Al2O3/SiO2 ratio is explained based on the relative change in covalency. Based on photoluminescence studies, site preference of Eu2+-doped mullite is assigned to structural cavity rather than to 6- or 4-coordinated regular lattice sites. (C) 2000 Elsevier Science S.A. All rights reserved.