We have studied the photoluminescence properties of Eu2+ in mullite. The 0.005 mol Eu2+- activated Al/Si = 1/2 mullite shows a single broad-band emission character and an emission band at about 435 nm. The emission band shifts slightly to a longer wavelength with an increase in Eu2+ concentration because the distance between Eu2+ ions decreases and the probability of energy transfer among Eu2+ ions increases with increased Eu2+ concentration. However, Al/Si = 1/1 mullite shows two emission centers, an Eu-1- and an Eu-2- site, which peak at 420 and 482 nm. Also, we investigated the compositional dependence of the luminescence properties of the Eu2+ ions based on the different Al/Si ratios. (C) 2003 The Electrochemical Society.