Template-Assisted Solid-State Synthesis And Its Mechanism Of RE-doped Phosphors At Low Temperatures

The purpose of this thesis is to develop a kind of template which can direct thesynthesis of luminescent materials (such as RE-doped phosphates or vanadates) viasolid-state reaction at low temperatures.All RE-doped phosphors were obtained by heating a stoichiometric mixture ofcorresponding precursors including some raw materials to form the templates at lowtemperature (650℃). Comparing with the traditional method of solid-state reaction,the reaction temperature was reduced to less than 700℃. Some factors such astemperature, the quantity of template were also discussed.The phosphors we synthesized were characterized by X-ray power diffraction(XRD), infrared spectra (IR), Raman spectra and Potoluminescence spectra (PL). ForLaPO₄ matrix doped with the template (Na_0.3Li_0.7PO₃)_n, its XRD data, IR and Ramanspectra suggest that their structure is monoclinic, isostructural with monazite, with achain of polyphosphate (Na_0.3Li_0.7PO₃)_n embedding in the channels to the directions ofc-axes of LaPO₄ lattices. Its unit-cell composition can be regarded asLaPO₄.n(0.3Na,0.7Li)PO₃:RE (RE=Eu or Ce-Tb). On the other hand, for YVO₄matrix doped with the template (Na_0.3Li_0.7PO₃)_n shows tetragonal, mainlyisotructural with xenotime. Under UV radiation, the relative emission intensities oftemplate-containing phosphors LaPO₄:Ce³⁺, Tb³⁺and YVO₄:Eu are stronger than thoseof the commercial phosphors LaPO₄:Ce³⁺, Tb³⁺ and Y₂O₃:Eu. Among them, therelative emission intensities of template-containing phosphors YVO₄·0.5(0.3Na,0.7Li)PO₃:Eu³⁺, YVO₄·(0.3Na, 0.7Li)PO3:Eu³⁺ are 2.47, 1.75 times higher than thoseof the commercial phosphor Y₂O3:Eu, respectively.A new green phosphor with formula NaLaP₂O₇:Ce³⁺,Tb³⁺ was synthesized viasolid-state reaction at low temperature up to 700℃fa(?) lower thar those o(?) corresponding commercial green phosphors (Ce,Tb)MgAl₁₁O₁₉and LaPO₄:Ce³⁺,Tb³⁺(which formed at 1600℃and 1400℃). Its structure can be indexed into anorthorhombic system. The optimum concentrations of Ce and Tb for this phosphorlocate at 0.3, 0.4 (per mol matrix), respectively. When excited by its maximumexcitation wavelength, the emission intensity of NaLaP₂O₇:Ce_0.3³⁺, Tb_0.4³⁺ is 43%higher than that of the commercial phosphor (Ce,Tb)MgAl₁₁O₁₉.