Rare Earth Modified Molybdate Luminescent Materials For LED

Luminescent materials have playing an important role due to their wide applications in the field of solid state lighting,full-color display and biological imaging.Rare earth have a great influence on spectroscopy,and the materials which doped with rare earth can improve the energy utilization efficiency and the performance of light emitting devices in the field of full-color display and vehicle lighting.Both doping ions and material host have an influence on the properties of the luminescent materials.Recently,there have a growing interest on the preparation of rare earth doped molybdates luminescent materials because of the simple preparation method,excellent physical and chemical stability,lower phonon energy of it.Meanwhile,molybdates is an important materials for the host,expecially for it play the part of the host of the white light-emitting diode?LED?phosphor,because it can match well with near ultraviolet chip.In this work,a series of Eu³⁺?Sm³⁺?Tb³⁺?Dy³⁺ doped and Eu³⁺,Dy³⁺ codoped NaY?MoO₄?₂ phosphors were synthesized by a traditional solid-state reaction,and Eu³⁺ doped NaY?MoO₄?₂ phosphors prepared by a oxidation of graphene assist solid-state method were also investigated.The PL spectra as well as their concentration quenching mechanism,energy mechanism,chromaticity diagram?CIE?,lifetime and thermal quenching were analyzed in detail.?1?A series phosphors of NaY_?1-x??MoO₄?₂:xRe³⁺?Re=Eu?Sm?Tb?Dy?were synthesized by a solid-state reaction.The microstructure,crystal structure and luminescence properties were investigated by X-ray diffraction?XRD?,scanning electron microscopy?SEM?and fluorescence spectrophotometer.The phosphors possessed scheelite tetragonal crystal structure.The crystallite size of the samples which doped with Eu³⁺?Sm³⁺?Tb³⁺?Dy³⁺ was between 5¹0?0.4⁰.85?1¹.5?0.2⁰.9 nm,and the samples showed red,reddish,green and yellow emitting under the exciting at 466?406?487?405 nm.The lifetime of the samples were 0.39?0.26?0.30?0.47 ms.The sample doped with Eu³⁺ didn't show concentration quenching clearly,while the phosphor showed thermal quenching obviously.The samples doped with Sm³⁺?Tb³⁺?Dy³⁺ showed concentration quenching and thermal quenching obviously through the studied on the concentration and temperature stability.?2?A series phosphors of NaY?0.92-x??MoO₄?₂:0.08Dy³⁺,xEu³⁺ were synthesized by a solid-state reaction,the samples had a scheelite tetragonal crystal structure which possessed a space group I41/a,the incrememt of Eu³⁺ ion concentration had less influence on the structure.Under the SEM,the sample had double tapered structure and the crystallite size of the samples was between 300⁸00 nm.the fluorescence spectrophotometer were used to analysize the luminescence properties.The result showed the tunable photoluminescence can realize by excited under different wavelenghths.When excited under 389 nm,the sample exhibited emission peaks centered at 573 nm?4F9/2?6H13/2?and 615 nm?5D0?7F2?.The integrated emission intensity of Eu³⁺ was increased while that of Dy³⁺ was decreased with the increased of Eu³⁺ concentration,which was attributed to the energy transfer from Dy³⁺ to Eu³⁺ ions.The ET efficiency achieved nearly 50 % of its maximum value when the concentration was 0.12,and the ET from Dy³⁺ to Eu³⁺ ions was electric dipole-dipole interaction mechanism,the critical distance was 13.5709 ?.The lifetime of Dy³⁺ decreased from 87.11 ?s to 27.06 ?s and Eu³⁺ decreased from 320.98 ?s to 256.17 ?s.The emission color of the sample changed from yellow to reddish region with increasing the Eu³⁺ ion concentration.?3?A series phosphors of NaY_?1-x??MoO₄?₂:xEu³⁺ were synthesized by a oxidation of graphene assist solid-state method.The XRD,SEM and fluorescence spectrophotometer were employed to characterize the synthesized samples.The result showed the samples had a structure of scheelite tetragonal,the crystallite size of the samples was about 4 ?m long and 2 ?m wide.Under the excitation of 466 nm,the samples exhibited strong red emission and the emission peaks centered at 615 nm,which was attribute to the 5D0?7F2 transition of Eu³⁺ ion.The concentration of Eu³⁺ ion had less influence on the intensity of the emission.The CIE showed the samples change to red region with the increment of Eu³⁺ ion concentration.The lifetime of the sample was 0.38⁰.39 ms.The phosphor showed thermal quenching obviously due to the radiative transition.This kind of phosphors which possessed excellent crystal structure,uniform dispersion,uniform particle size and great luminescence properties can be prepared by this method.All the results showed the samples which prepared by traditional solid-state reaction had strong red?reddish?green and yellow emission.It had potential application in the field of light-emitting diode.Eu³⁺ and Dy³⁺ co-doping NaY?MoO₄?₂ have varies of emission color under differernt doping concentration,suggesting that color-tunable phosphors may have promising applications in color displays and lighting fields.The samples which prepared by a oxidation of graphene assisted solid-state method possessed excellent crystal structure,uniform dispersion,uniform crystallite size.The synthesis method had simple process and large output,and provided a new thought to prepare samples which had excellent structure for industrial production,meanwhile,all the results shows such kind of phosphors had potential application in the fields of solid-state lighting.