Preparation And Luminescence Properties Of Rare Earth Ions Doped MAl₂Si₂O₈?M=Sr,Ba? Phosphors For W-LEDs

As the hotspot in solid-state lighting areas,the white light-emitting diodes have attracted significant attention due to the advantages of high luminous efficiency,energy-saving,safety,reliability,long lifetime and environmental friendly.Up to now,the white light-emitting diodes can be obtained through combining a blue chip with commercial yellow-emitting phosphors.However,the white light-emitting diodes used above method in the practical application have some defects,such as low efficiency and the poor color-rending index.The other method to achieve the white light-emitting diodes is combining the red,green and blue color phosphor with ultraviolet or near ultraviolet light-emitting diodes chip.Compared with the conventional blue In-GaN chip method,through the tricolor phosphors to convert the radiation of near ultraviolet chips to obtain the white light is a good method,which is considered to be more stable and efficiency.Moreover,the color rendering index of multicolor phosphors gets further improvement campare with monochrome phosphor.About the host of phosphor,aluminosilicate compounds are good candidates as host structures due to several advantages,such as excellent physical and chemical properties,high efficiency and thermal stability,which have drawn much attention.In this paper,some multicolor phosphors were synthesized by co-doping two rare earth ions into aluminosilicate host.The crystal structure,luminescent characteristic,energy transfer and thermal stability have been detail investigated.Specific research includes the following several aspects:1.A series of Tb³⁺ or/and Bi³⁺ doped BaAl₂Si₂O₈ phosphors were synthesized via solid-state method.The structural refinement of XRD was made using GSAS to study BaAl₂Si₂O₈ crystal structure.The optimum concentrations of Bi³⁺ and Tb³⁺ were 1.5at.% and 7at.%,respectively.Upon UV excitation,BaAl₂Si₂O₈:0.015Bi³⁺ and BaAl₂Si₂O₈:0.07Tb³⁺ phosphors emitted blue and green light and the emission color of BaAl₂Si₂O₈:Bi³⁺,Tb³⁺ could be tuned from blue to green by changing the proportion of Bi³⁺ and Tb³⁺.With constantly increasing Tb³⁺ concentrations,the energy transfer efficiency from Bi³⁺ to Tb³⁺ in BaAl₂Si₂O₈ host increased gradually and reached as high as 86.54%,the quantum yield was about 44.26%.The energy transfer mechanism(Bi³⁺-Tb³⁺)was proved to be dipole-dipole interaction by fluorescence spectra and lifetime.The Tb³⁺ emission intensity can be considerably enhanced when monitored at NUV?377 nm?by co-doping Bi³⁺ ion.Over 200 ?,72% initial emission intensity can still be remained.2.Single-component and white light-emitting phosphors BaAl₂Si₂O₈:Dy³⁺,Eu³⁺ were prepared via the conventional solid-state reaction method.The optimum doping concentrations of Dy³⁺ and Eu³⁺ are both 5at.% for Dy³⁺ or Eu³⁺ singly doped BaAl₂Si₂O₈.This energy transfer from Dy³⁺ to Eu³⁺ was confirmed and investigated by photoluminescence spectra and the decay time of energy donor Dy³⁺ ions.The energy transfer mechanism(Dy³⁺-Eu³⁺)was proved to be dipole-dipole interaction.Upon 348 nm excitation,BaAl₂Si₂O₈:Dy³⁺,Eu³⁺ phosphors can be effectively emit visible light from yellow to white by altering the concentration ratio of Dy³⁺ and Eu³⁺.3.Ce³⁺,Tb³⁺ singly and co-doped SrAl₂Si₂O₈ phosphors were synthesized by solid-state reaction method.The crystal structure,photoluminescence excitation and emission spectra,decay lifetime,energy transfer,quantum yield and thermal stability have been detail investigated.The optimum concentrations of Ce³⁺ and Tb³⁺ are determined to 4at.% through the emission spectra.SrAl₂Si₂O₈:Ce³⁺,Tb³⁺phosphors exhibit intense green emissions at 488,541,584 and 620 nm,which correspond to the 5D4-7FJ characteristic level transition of Tb³⁺ ion;meanwhile,a weak band peak at 430 nm of Ce³⁺ is exist.In addition,the solid-state synthesized SrAl₂Si₂O₈:0.04Ce³⁺,0.04Tb³⁺ phosphor powders have comparable green luminescence properties and better thermal stability compared with available commercial green phosphors,the quantum yield was about 67.37%.