Crystallographic and luminescent properties of orthorhombic BaAl_2S_4:Eu powder and thin films

摘要

BaAl_2S_4:Eu thin films were prepared from a multilayered BaS:Eu/Al_2S_3 thin-film structure, deposited with electron-beam evaporation. Depending on the deposition and postdeposition annealing temperature, europium-doped BaAl_2S_4 thin films can show both an orthorhombic and the more common cubic crystal structure. The lattice constants of the orthorhombic BaAl_2S_4 are determined from powder-diffraction data. The photoluminescent properties of europium-doped orthorhombic and cubic BaAl_2S_4 powders are compared. The occurrence of both phases in thin films is discussed in terms of substrate and postdeposition annealing temperature. A temperature of 600℃ is sufficient to obtain the orthorhombic phase, and annealing at 900℃ leads to the cubic phase. The phase formation in the multilayered thin films is investigated by studying the Crystallographic, optical, and photoluminescent properties.