The optical properties of BaAl2S4 doped with Eu2+ were investigated. The synthesis was performed in evacuated and sealed quartz ampul at 1000 degrees C during 1 h, then at 840 degrees C during 20 h. With absorption, excitation, and emission spectra we have determined the crystal- field splitting, the redshift, the influence of the lattice vibration properties, and the thermal quenching of the luminescence. The crystal- field splitting of Eu2+ in BaAl2S4 was estimated on the order of 8000 to 10 000 cm(-1) and the Huang-Rhys parameter S = 5 +/- 1 corresponds to an intermediate electron-phonon coupling regime. The mean phonon energy for BaAl2S4 was evaluated by optical and Raman methods, and the obtained values were 32 +/- 5 and 40 meV, respectively. These results confirm the very interesting properties of this blue BaAl2S4: Eu2+ phosphor, the most important being the very slight thermal quenching of the luminescence. (c) 2006 The Electrochemical Society.