Study On The Preparation And Luminescent Properties Of Rare Earth Doped Fluorescent Materials For Near Ultraviolet Excited White LED

White light-emitting diodes（w-LEDs）are penetrating the lighting market at an extremely fast rate owning to their low electric consumption,environment-friendliness,high brightness,long lifetime,good reliability,and fast response,etc.The commercial w-LEDs that consists of a blue LED chip and Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)yellow-emitting phosphor cannot achieve a warm white light with a low color rendering index（CRI<80）and a high correlated color temperature（CCT>4500 K）.In contrast,w-LEDs fabricated with n-UV LED chips and tricolor（red,green and blue）phosphors are expected to dominate the market in the near future.In view of this,it is urgent to study the rare earth phosphor materials which can be used in white LED.In this paper,a series of rare earth ion doped tantalum,niobium and silicate luminescent materials were synthesized by traditional high temperature solid state method,and the phase purity,crystal structure,fluorescence spectrum,thermal stability and fluorescence lifetime decay curve of the materials were analyzed systematically.（1）A new type of red phosphor M₂YTa O6:Eu³⁺（M=Sr,Ba）red phosphor was prepared by traditional solid state reaction method,and its crystal structure,photoluminescence properties,thermal stability and decay lifetime were studied in detail.The excitation and emission spectra of the samples are analyzed and discussed in detail.Under the near ultraviolet excitation,due to the ⁵D₀→⁷F₂ level transition,the Sr₂YTaO₆:Eu³⁺sample has a strong red emission peak at 612 nm,and the sample Ba₂YTaO₆:Eu³⁺has a strong orange-red emission at 592 nm due to the ⁵D₀→⁷F₁transition.（2）A series of Bi³⁺/Eu³⁺single-doped and co-doped Ba₂ScTaO₆phosphors were prepared by traditional high temperature solid state reaction method.The structure and luminescence properties of the samples were studied systematically by X-ray diffraction（XRD）,scanning electron microscope（SEM）,fluorescence spectra and lifetime decay curves.The observation of XRD pattern shows that all the samples are pure phase.Under the excitation of ultraviolet light,the luminous color of Ba₂ScTaO₆:Bi³⁺,Eu³⁺can be transferred through the energy of Bi³⁺-Eu³⁺,and the color transformation from fuchsia to orange can be realized by the ratio of Bi³⁺/Eu³⁺.In addition,the energy transfer mechanism,luminescence attenuation curve and chromaticity coordinates are discussed in detail.（3）A new double perovskite structure tantalate orange-red phosphor Sr₂LuTaO₆:Sm³⁺was synthesized by solid state reaction,and its phase,crystal structure,photoluminescence properties,thermal stability and attenuation curve were studied.X-ray diffraction patterns show that the phosphor is a pure phase with cubic structure.Under the near ultraviolet excitation of 407 nm,the samples have strong emission peaks at 564 nm,600 nm and 645 nm,respectively,due to the ⁴G_5/2→⁶H_Jlevel transition.The optimum doping concentration of Sm³⁺ions is 5 mol%,and the concentration quenching process comes from the energy transfer between neighboring ions.The prepared phosphor has good thermal stability,and the integral strength at423K is still 91.10%of the initial strength.The CIE chromaticity coordinates of Sr₂LuTaO₆:Sm³⁺phosphors are located in the orange-red region.（4）A series of Tm³⁺and Dy³⁺ions single-doped and co-doped Na₃Sc Si₂O₇phosphors were prepared by traditional solid-state reaction method.The X-ray diffraction,photoluminescence properties,fluorescence attenuation curve and energy transfer behavior of the samples were studied.XRD spectra show that all the diffraction peaks of the samples are consistent with the JCPDS standard data.Under UV excitation,Na₃Sc Si₂O₇ phosphors doped with Tm³⁺and Dy³⁺ions show blue and yellow emission.The luminous color of Na₃Sc Si₂O₇:Tm³⁺,Dy³⁺can be adjusted by the corresponding Tm³⁺-Dy³⁺energy transfer.In addition,the chromaticity coordinate of Na₃Sc Si₂O₇:0.04Tm³⁺,0.13Dy³⁺is（0.3195,0.3214）,which is close to the ideal white light（0.33,0.33）.（5）A new perovskite-type orange-red phosphor Ba₂Sc NbO₆:x Eu³⁺was designed and synthesized by solid phase synthesis.The prepared samples were characterized by X-ray diffraction,luminescence properties,fluorescence decay time and thermal stability.X-ray diffraction confirmed that BSN:x Eu³⁺has a cubic structure and the space group is Pm-3m（221）.The photoluminescence excitation spectrum consists of a wide charge transfer band of（CTB）and Eu³⁺ions.The emission spectrum shows that there is a strong at 595 nm.The energy transfer mechanism between Eu³⁺ions in Ba₂Sc NbO₆ has been proved to be dipole-dipole interaction.In addition,Ba₂Sc NbO₆:x Eu³⁺phosphors have obvious thermal quenching characteristics,and the emission intensity at 423 K is still more than 71%of the initial value at room temperature.