Structural and photoluminescence properties of Dy3+ co-doped and Eu2+ activated MAl2O4 (M = Ba, Ca, Sr) nanophosphors

Abstract

Long afterglow alkaline earth aluminates MAl2O4:Eu, Dy (M: Ca,Sr,Ba) phosphors are generally synthesized by the solid-state process which is more feasible than other conventional processes in terms of operation and large-scale production. However, the constituents of phosphors synthesized using this process are usually not mixed well, the particles agglomerates and very high temperature requirement to synthesize the final powder make it undesirable. In order to circumvent these problems, MAl2O4:Eu, Dy (Ca,Ba,Sr) phosphors were prepared at low temperatures (500°C) by the solution–combustion of corresponding metal nitrate–urea solution mixtures, over a time of 5–10min. In order to elucidate the relationship between the constituent, structure and PL properties product’s particle size, morphological and structural properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), while the characteristic luminescence properties were investigated using emission spectra. The low temperature monoclinic structure for both CaAl2O4 and SrAl2O4 and the hexagonal structure of BaAl2O4 were observed. The emission spectra of these phosphors indicated that all of them are broad band, and the only emission peaks around 448, 490 and 515nm of CaAl2O4:Eu, Dy, BaAl2O4:Eu, Dy and SrAl2O4:Eu, Dy, respectively, are due to 5d→4f transition of Eu2+. The decay curves implied that these phosphors contain fast, medium and slow-decay process. The Dy3+ trap levels may be considered to be responsible for the long afterglow phosphorescence at room temperature.