Structure and Luminescence Properties of Sr4Al14O25:Eu2+, Dy3+ by Ba2+ Substitution

The rare-earth doped strontium aluminate phosphors Sr4-xBaxAl14O25:Eu2+,Dy3+ (x=0, 0.8, 1.6, 2.4, 3.2, 4) were synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors were characterized by X-ray diffraction. The results show that the monoclinic SrAl2O4 and hexagonal SrAl12O19 co-exist in the sample with x=0.8. The major phase of phosphors is hexagonal BaAl2O4 when x>1.6. It is indicated that the phase structure of the samples changes from Sr4Al14O25 to BaAl2O4 when the value of x changes from 0 to 4. The emission spectra of 360 nm irradiation reveal that Eu2+ is the luminescence center of the samples due to 4f(6)5d-4f(7) transition of Eu2+ electron. With the Ba doping content increasing, the shift of emission spectra peak occurs, because the lattice shrinkage caused by Sr2+ substitution for Ba2+ affects the 5d level cleavage of Eu2+ and thus influences the 4f(6)5d-4f(7) transition. The afterglow spectra show that Eu2+ of BaAl2O4 is the luminescence center for the products when x>1.6. The decay characteristics show that the phosphor samples with different Ba2+ content have different afterglow time, and the afterglow time also changes with the value of x. The measurement of thermoluminescence reveals that the trap depth of the phosphor samples with different Ba2+ content is different, and the samples with deeper traps have longer afterglow time.