Structure and luminescence properties of SrAl2O4:Eu2+, Dy3+ by Ba2+ and Ca2+ co-doping

The long afterglow phosphors with Ca and Ba co-doped equally in SrxCa(1−x)/2Ba(1−x)/2Al2O4:Eu2+,Dy3+ (x = 1.0, 0.8, 0.6, 0.4, 0.2, 0) were synthesized using high temperature solid-state reaction method. X-ray powder diffraction (XRD) patterns show that the crystal phase structure of SrAl2O4 changes from monoclinic to hexagonal with the decrease of x from 1 to 0.6, and hexagonal BaAl2O4 and monoclinic CaAl2O4 coexist when x is 0.2. Nevertheless, when x is reduced to 0, the main phase of sample changes to BaAl2O4. A blue shift is observed in the emission spectra due to the change in nature of the Eu2+ surroundings when x changes from 0.6 to 0. The results given by scanning electronic microscope (SEM) show that phosphors with different structures have similar irregular morphology. The decay characteristics reflect that the phosphors with different structures have different afterglow time. Samples with monoclinic structure have longer afterglow time than samples with hexagonal structure. The measurement of thermoluminescence reveals that the monoclinic structure of the phosphors provides better sites than that of the hexagonal structure for Dy3+ions to generate suitable trap level.

► SrxCa(1-x)/2Ba(1-x)/2Al2O4:Eu2+,Dy3+ phosphors were prepared. ► The high temperature phase of SrAl2O4 was obtained at room temperature. ► The emit colour of phosphors can be adjusting by the radio of x. ► The monoclinic structure provide better lattice sites to generate trap level.