Preparation And Luminescent Properties Of Bluish Purple Aluminate Long Afterglow Phosphors

The aluminate long afterglow phosphors doped with rare earth as a non-radioactive phosphors have excellent luminescent property. Furthermore the aluminate long afterglow phosphors have no environmental pollution in the process of preparation and use, which make the phosphors have wide application prospect. In recent years, the research reports of the aluminate long afterglow phosphors appear in succession. The emphasis of the researches is the long afterglow phosphors doped with rare earth elements, especially the alkaline earth aluminate system. In this thesis, CaAl₂O₄-based long afterglow phosphors doped with Eu²⁺ and other assistant activators are studied. The luminescent brightness and time of the phosphors can be improved greatly by adjusting the concentrations of the activators in the proper range and the compositions of the host. Other factors that affect the luminescent properties of the long afterglow phosphors are also studied. The luminescent mechanism of the long afterglow phosphors is elementarily discussed. The experiments reveal that the luminescent brightness of the CaAl₂O₄:Eu²⁺, Nd³⁺ long afterglow phosphors greatly depends on the concentration of Eu²⁺. When the content of Eu²⁺ is 0.005 mol/mol, the luminescent brightness is the best. When the raw materials doped with assistant activator of Nd³⁺,the luminescent brightness of phosphors enhanced obviously,and the luminescent time also prolonged. In the process of preparation of CaAl₂O₄:Eu²⁺, Nd³⁺, a little superfluous aluminum can enhance the brightness of the phosphors. The effects of different flux on CaAl₂O₄:Eu²⁺, Nd³⁺ long afterglow phosphors are discussed. When H₃BO₃ joined as flux, the brightness of the long afterglow phosphors is better than that doped with other flux. When the content of H₃BO₃ is 1.6%(wt), the brightness of phosphors is the best. The thermal stability of CaAl₂O₄:Eu²⁺, Nd³⁺ is researched. The thermal stability of the aluminate long afterglow phosphors is better than that of sulfide long afterglow phosphors apparently. CaAl₂O₄:Eu²⁺, Nd³⁺, RE³⁺, which is new type long afterglow phosphors, is synthesized for the first time. Its luminescent properties are better than that of CaAl₂O₄:Eu²⁺, Nd³⁺ long afterglow phosphors, which shows that more trap energy levels are produced when RE³⁺ is added. RE³⁺ possesses proper affinity toward to the electrons in the energy level, which can release electrons slowly and produce long afterglow luminescence at the same time. Through the thermoluminescence (TL) glow curves gained from doping different RE³⁺, the trap energy level is estimated by peak shape method. The luminescent mechanism of long afterglow phosphors doping rare earth ions is discussed and analyzed. In our opinion, when the phosphors are excited, the electrons are seized by the traps, after the excitation, the electrons absorb heat energy and escape from the traps, and the energy is transferred to the excited state of Eu²⁺. Then the transition to the ground state leads to the characteristic emission of Eu²⁺. The escape of the seized electrons from the traps is a persisting process, which causes the long afterglow luminescence.