| At present,the phosphor conversion white light-emitting diode(pc-wLED)is one of main ways to realize the white light.pc-wLEDs are studied and used widely due to its long lifetime,high quantum efficiency,and the advantage of no harm to the environment.Phosphors mainly consist of matrix and activator.Although it is well known that the properties of activator ions determine the luminescence properties of phosphors.The phosphor matrix materials play a very important effect on the luminescence of the luminescent ions,and the same luminescent ion may show different luminescence properties in different matrix materials.In addition,changing the local environment of the luminescent ions in the matrix lattice structure can also lead to some changes in the luminescence properties of the luminescent ions.Eu2+ always exhibits a broad-band emission derived from its 5d-4f electron transition,so it can be used as an effective activator in many matrix materials.And its exposed 5d orbital is particularly sensitive to the crystal field environment,the change of the chemical environment can tune the emitting color of Eu2+.Therefore,Eu2+ doped phosphors usually have wide excitation bands and strong emission in the range of near ultraviolet and red.In this paper,the luminescence properties of phosphate phosphors doped with Eu2+ were effectively regulated by changing the geometric environment around Eu2+in the matrix lattice structure.The contents are as follows:1.In this work,we synthesized a series of different concentration of K+ doped Sr8.94Mg1.5-0.5xKx(P04)7:0.06Eu2+(x = 0,0.25,0.25,0.5,1.0)phosphors by high temperature solid state method.XRD data show that Sr9Mg1.5(PO4)7 host belongs to hexagonal,its space group is R-3m(166).Then we systematically studied their structure and luminescence properties by a series of measurements such as X-ray powder diffraction(XRD),excitation and emission spectra(PLE and PL),solid ultraviolet absorption spectrum,Raman spectrum,thermal stability and so on.As a result,with the content of K+ increasing,the luminescence of repaired phosphate phosphor is enhanced,and the internal and external quantum efficiency significantly increases by 50.5%and 55.4%,respectively.Additionally,the thermal stability is also a little improved.The enhancement mechanisms in luminescence are discussed in details based on the investigations of microstructure and luminescence spectra.We find that the low luminescence efficiency is due to the existence of vacancies in the phosphor.The white LED packages using the repaired Sr9MgK(PO4)7:Eu2+ phosphor demonstrates a low correlated color temperature(?2900 K),high color rendering index(?90)and R9>91.We expect that the strategy proposed herein would improve luminescence for other phosphors with vacancy defects.2.In this experiment,we firstly synthesized Ba2Ca(P04)2 matrix material by high temperature solid state method,and analyzed its crystal structure.In order to improve the luminescence properties of Ba7Ca3.5(PO4)7:Eu phosphor,then we similarly introduced alkali metal ion K+ to the phosphor and prepared a series of Ba7Ca3.5-0.5XKx(PO4)7:Eu(x =0?1.0)phosphors.We have analyzed their crystal structure and compositional variation through X-ray powder diffraction(XRD),Raman,Scanning electron microscope(SEM),X-ray energy dispersive spectral analysis(EDX).And their luminescence properties were studied by fluorescence,decay time,thermal stability and quantum efficiency measurements.We found that the addition of alkali metal ion K+ not only improved the luminescence intensity of the phosphors,but also its thermal stability and quantum efficiency.Finally,we further encapsulated a warm white LED device,and got its color coordinates,color temperature,and color rendering index,which demonstrate that Ba7Ca3K(PO4)7:Eu phosphor can be effectively applied in w-LEDs. |
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