Synthesis And Properties Of Rare Earth-doped Composite Metal Oxides Phosphors For White Light-emitting Diodes

White light-emitting-diode,combining?N?UV-LED chips with multicolor phosphors,has attracted much attention on account of its high color rendering index,high luminous efficiency,stable color temperature,adjustable color,energy saving,and environmental friendliness characteristics.A suitable phosphor is one of the key elements in white light LED combination mode.In this dissertation,we have synthesized a series of rare earth-doped composite metal oxides phosphors,which can be excited by?N?UV-LED chips.The X-ray diffractometer?XRD?,field-emission scanning electronic microscope?FE-SEM?,high resolution transmission electron microscopy?HRTEM?,diffuse reflection spectra?UV-vis DRS?,photoluminescence?PL?,and fluorescent decay lifetimes were utilized to characterize the prepared phosphors.Due to their excellent luminescence properties,the prepared phosphors have potential application in?N?UV-LED devices.1.A series of La₂Zr₃?Mo O₄?₉ and La₂Zr₃?Mo O₄?₉:Ln³⁺(Ln³⁺=Dy³⁺and/or Eu³⁺)nanocrystalline phosphors were synthesized via a citrate sol-gel method.The XRD results reveal that the prepared La₂Zr₃?Mo O₄?₉:Ln³⁺(Ln³⁺=Dy³⁺and/or Eu³⁺)nanocrystalline phosphors present a single-phased trigonal crystal structure.FE-SEM and HRTEM images indicate that the prepared La₂Zr₃?Mo O₄?₉:Ln³⁺phosphors consist of fine and spherical grains with the size of around 35-60 nm in diameter.Under the excitation of ultraviolet light,the La₂Zr₃?Mo O₄?₉ host lattice presents a characteristic blue broadband emission of Mo O₄ group from 300 to 550nm peaking at 399 nm,and the La₂Zr₃?Mo O₄?₉:Ln³⁺phosphors show the characteristic emissions of Dy³⁺(⁴F_9/2-⁶H_15/25/2 and ⁴F_9/2-⁶H_13/2 transitions)and Eu³⁺?⁵D₀-⁷F_J,J=1,2,3,and 4 transitions?,respectively.There exists an energy transfer from the La₂Zr₃?Mo O₄?₉ host lattice to Dy³⁺and Eu³⁺ions in La₂Zr₃?Mo O₄?₉:Ln³⁺phosphor.The luminescence color of La₂Zr₃?Mo O₄?₉:Ln³⁺phosphors can be tuned from blue-white,white to orange-red by adjusting the doping concentration of Dy³⁺to Eu³⁺and the relative ratio of Dy³⁺to Eu³⁺in La₂Zr₃?Mo O₄?₉ host lattice.2.Gd₂Nb₂Ti O₁₀ and Gd₂Nb₂Ti O₁₀:Ln³⁺(Ln³⁺=Tm³⁺and/or Eu³⁺)sosoloid phosphors were synthesized a citrate sol-gel synthesis method.The XRD results reveal that the solid solution compounds Gd₂Nb₂Ti O₁₀ is composed of GdNb Ti O₆and Gd Nb O₄,and the prepared Gd₂Nb₂Ti O₁₀:Ln³⁺(Ln³⁺=Tm³⁺and/or Eu³⁺)phosphors present a multiphase crystal structure.FE-SEM and HRTEM images indicate that the prepared Gd₂Nb₂Ti O₁₀:Ln³⁺phosphors consist of fine and spherical grains with the size of around 335-570 nm in diameter.Under the excitation of ultraviolet light,the obtained Gd₂Nb₂Ti O₁₀ sosoloid phosphor presents a strong yellow-green luminescence from 300 to 660 nm centered at 508 nm,and the Gd₂Nb₂Ti O₁₀:Ln³⁺sosoloid phosphors show both the host lattice emission and respective emission lines derived from the characterize f-f transitions of the doping Tm³⁺and Eu³⁺ions.The luminescence color of Gd₂Nb₂Ti O₁₀:Ln³⁺phosphors can be tuned from blue to yellow-green,white,pinkish,red,etc.via varying the doping species,concentration,and relative ratio of the co-doping rare earth ions in Gd₂Nb₂Ti O₁₀ host lattice.3.A series of?Ba,Ca?₅?PO₄?₂Si O₄:Eu²⁺phosphors were synthesized via a conventional solid-state reaction and citrate sol-gel synthesis method.The XRD results indicated that the pure Ba₅?PO₄?₂Si O₄ phase can be obtained by different synthesis method,there is no crystal lattice perturbation induced by the doping the ions Ca²⁺and Eu²⁺.The Ba₅?PO₄?₂Si O₄:Eu²⁺phosphors prepared by a conventional solid-state reaction show strong blue-green.However,the Ba₅?PO₄?₂Si O₄:Eu²⁺phosphors prepared by sol-gel synthesis method show blue luminescence.Under the excitation of ultraviolet light,the?Ba,Ca?₅?PO₄?₂Si O₄:Eu²⁺nanocrystalline phosphors consist of a broad band in the range of 400-550 nm due to the4f⁶5d¹-4f⁷(⁸S_7/2)charge transfer transitions of Eu²⁺ions.The luminescence color of?Ba,Ca?₅?PO₄?₂SiO₄:Eu²⁺nanocrystalline phosphors can be tuned from deep blue to blue,thirsty blue via varying the concentration of the doping rare earth ion Eu²⁺in?Ba,Ca?₅?PO₄?₂SiO₄ host lattice.High quality blue light emission can be achieved in the phosphor(Ba_0.99Ca_0.01)₅?PO₄?₂Si O₄:Eu²⁺by accurately adjusting the doping concentration of Eu²⁺ions.