Atomic composition and structural properties of blue emitting BaAl2S4:Eu electroluminescent thin films

We have investigated the compositional and structural properties of blue emitting BaAl2S4:Eu electroluminescent thin films fabricated by switching electron-beam evaporation using two targets. The use of X-ray photoelectron spectroscopy (XPS) revealed that the ratio of barium to sulfur in thin films is 1.0 : 2.0, which is identical to the stoichiometry of BaAl2S4. The X-ray diffraction (XRD) peaks from the thin film were assigned to those of a BaAl2S4 crystal. The photoluminescence (PL) spectrum shows emission from the 4f(6)5d --> 4f(7) transition of the activated Eu2+ ions in BaAl2S4 crystals. These results indicate that the crystalline phase in thin films is only BaAl2S4. The thin films also contain a large amount of oxygen impurities, which result in the formation of an Al2O3 layer and amorphous barium aluminate.