Study On Preparation And Properties Of Dy³⁺ Activated Y₂O₂S-based White Light Long-lasting Phosphors

Long-lasting phosphors are a special kind of functional materials, which can be widely used in a lot of fields such as evacuation indicator lighting, coating, military facilities and medical system. From the point of practical application, a white afterglow phosphor is most suitable as illuminating light source. Therefore, the white-light long-lasting phosphors with high luminescence efficiency and good chemical stability are badly needed. Considering the superiority of Y2O2S matrix and emission spectrum of Dy3+, so a large number of efforts have been focused on the improvement of the luminescence properties of Dy3+activated Y2O2S-based white light long-lasting phosphors.Firstly, Y2O2S:Dy3+, M2+, Z4+white-light long-lasting phosphors doped with different kinds of divalent or quadrivalent ions were synthesized by a traditional solid-state reaction. Secondly, Y2O2S:Dy3+, Mg2+, Ti4+white-light long-lasting powders were prepared via sol-gel method, using EDTA as complexing agent. The samples were characterized by X-ray diffraction, photoluminescence spectroscopy, and thermally stimulated spectrometry. The results were shown as follows:(1) The crystal structure of Y2O2S has not been changed by co-doping with M2+ion(M=Mg, Sr, Ca, Ba) or Z4+ion(Z=Zr, Si, Ti, Nb). All of samples can emmit white light due to mixing of the dominating emissions centered at486nm (blue) and577nm (yellow), corresponding to4F9/2â†'6H15/2and4F9/2â†'6H13/2transitions of Dy3+, respectively. In addition, Y2O2S:1%Dy3+,6%Mg2+,6%Ti4+showed optimal luminescence properties. The CIE chromaticity diagram was (0.34,0.33) and the decay time could last for over2160s (≥1mcd/m).(2) Y2O2S:Dy3+, Mg2+, Ti4+white-light long-lasting phosphors were synthesized by sol-gel method. The results showed that the samples calcined under1200℃were composed of the pure Y2O2S phase. The results also shown that the absorption peak shifts to the red as the temperature increases. Under359nm UV excitation, the phosphor presented white luminescence due to mixing of the dominating emissions centered at488nm (blue) and579nm (yellow), corresponding to4F9/2â†'6H15/2and4F9/2â†'6H13/2transitions of Dy3+, respectively. When calcined at1200℃, the sample shows the optimal afterglow properties, and the CIE was (0.38,0.37), the trap depth E was1.1eV, the afterglow time could last for over3900s(≥1mcd/m2).(3)Y2O2S:X Dy3+, Mg2+, Ti4+(X=0.5,1,1.5,2%mol) white-light long lasting phosphors were synthesized by sol-gel method at1200℃. Both the fluorescence intensity and afterglow time reached the largest values in the phosphor Y2O2S:0.01Dy3+, Mg2+, Ti4+ (4) In order to further reduce the curing temperature, cosolvent is added. The results show that the synthesis temperature of the sample prepared via sol-gel method at1000℃and using cosolvent such as sodium carbonate and potassium phosphate is200℃lower than that of without cosolvent.