Synthesis, Energy Transfer And Tunable Luminescence Properties Of White-emitting Rare Earth-activated Phosphate Phosphors

Phosphate phosphor doped with rare earth is an important kind of luminescent material. They have many applications in the field of solid state lighting and display, due to their effective absorption in near UV region, good luminescent properties and stability. Eu2+, Ce3+ and Mn2+ are widely used as activators in the phosphate phosphors. In this thesis, a variety of phosphate phosphors were prepared, and their photoluminescence properties were systematically investigated in detail. It has provided a new train of thought for the research of the white-light-emitting phosphor-converted materials for UV-pumped lightemitting diodes.Na3Ca6(PO4)5:Eu2+,Ce3+; Na5Ca2Al(PO4)4:Eu2+,Ce3+; Na5Ca2Al(PO4)4:Eu2+,Mn2+, and Ca8NaRe(PO4)6F2:Eu2+,Mn2+(Re=Gd,La,Y) phosphors were prepared by the combustion-assisted synthesis method. We have systematically investigated their PL and PLE spectra, fluorescence quenching process, decay time, the energy transfer process between the ions and the control of luminous color coordinate of these phosphor.Firstly, we have introduced the research background of rare earth phosphor, introduced some synthesis methods, and analyzed the energy transfer and quenching of rare earth.Secondly, the experiment conditions such as reagents and instruments are introduced. The synthesis method and characterization of single-phased phosphors are also presented.Thirdly, the phosphors with various hosts in this thesis were perapred by the combustion-assisted synthesis method, and their crystal structures, luminescent properties and the energy transfer efficiency were investigated. Eu2+/Ce3+ co-doped Na3Ca6(PO4)5 phosphor shows a bright green emission under UV excitation. The luminescent intensity of Eu2+ was increased by 70% via the energy transfer from Ce3+ to Eu2+, which was validated and demonstrated to be a resonant type via the exchange interaction mechanism. Eu2+/Ce3+ and Eu2+/Mn2+ co-doped phosphors are synthesized. The influence of temperature on the crystal structure of Na5Ca2Al(PO4)4 was studied. In Na5Ca2Al(PO4)4:Eu2+, Ce3+, the luminescent intensity of Eu2+ increased 1.3 times by the energy transfer from Ce3+ to Eu2+. The emission color of Na5Ca2Al(PO4)4 phosphor codoped with Eu2+ and Mn2+ can be tuned from cyan to white gradually and eventually to orange by changing the ratio of Eu2+ and Mn2+. A series of Ca8NaRe(PO4)6F2: Eu2+,Mn2+(Re=Gd, La, Y) phosphors were syntheized and their crystal structures, luminescent properties, and the energy transfer processes were systematically investigated. The PL and PLE spectra of single and/or doubly doped phosphors were recorded, and the energy transfer from Eu2+ to Mn2+ was found. Also, the energy transfer efficiency between Eu2+ and Mn2+ was calculated based on the fluorescent spectra and fluorescent decay curves of the Eu2+/Mn2+ co-doped phosphor. The emission color of the Eu2+/Mn2+ codoped phosphor can be tuned by changing the concentration of Mn2+, and white light emission can be realized in the single-phased Ca8NaRe(PO4)6F2: Eu2+, Mn2+(Re=Gd, La, Y) phosphors.