The addition of ammonium chloride to a precursor solution improved the luminescence intensity of the BaMgAl10O17 : Eu2+ phosphor synthesized by spray pyrolysis without postheating. With this addition, the luminescence intensity under vacuum ultraviolet (146 nm) excitation was increased 1.6 times, and reached 88% of a commercial phosphor. The additive helped substance migration through the gaseous phase, and promoted crystal growth. The mechanism was examined based on the luminescence intensity data and equilibrium calculation results. (C) 2004 The Electrochemical Society.