A novel structural behavior of strontium aluminate (SrAl2O4 : Eu) synthesized by spray pyrolysis was found from the structural dependence of SrAl2O4 : Eu on the Eu concentration. Results revealed that all of the as- sprayed samples were a mixture of the structures of monoclinic and hexagonal phases. However, the structural behavior of the SrAl2O4 : Eu postannealed at 1300degreesC in a reducing atmosphere for 2 h strongly depended on the europium concentrations. With increasing europium concentration, a characteristic hexagonal phase can be observed in the postannealed samples. When 12% of the strontium is replaced by europium, the structure of the postannealed sample is purely hexagonal. The mechanism of the phase dependence of SrAl2O4 : Eu on europium concentration is discussed. (C) 2004 The Electrochemical Society.