Structure and luminescence properties of SrAl_2O_4:Eu~(2+), Dy~(3+) by Ba~(2+) and Ca~(2+) co-doping

摘要

The long afterglow phosphors with Ca and Ba co-doped equally in Sr_xCa_((1-x)/2)Ba_((1-x)/2)Al_2O_4:Eu~(2+),Dy~(3+) (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 SrAl_2O_4 changes from mono-clinic to hexagonal with the decrease of x from 1 to 0.6, and hexagonal BaAl_2O_4 and monoclinic CaAl_2O_4 coexist when x is 0.2. Nevertheless, when x is reduced to 0, the main phase of sample changes to BaAl_2O_4. A blue shift is observed in the emission spectra due to the change in nature of the Eu~(2+) 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 thermolumi-nescence reveals that the monoclinic structure of the phosphors provides better sites than that of the hexagonal structure for Dy~(3+)ions to generate suitable trap level.