The Synthesis And The Photoluminescence Properties Of Aluminate Phosphors

At present,full colour displays made of phosphor-converted light emitting diodes?pc-WLEDs?,which are energy-efficient,compact and rigid,long-lived and environmental friendliness,have received worldwide attention.It was known as the fourth generation of lighting source.This paper want to seek a new phosphor for aluminate fluorescent material,which have high efficiency,high color rendering index of white LED.The RE³⁺(Ce³⁺,Eu²⁺,Sm³⁺,Bi³⁺,Tb³⁺)doped in LaSr₂AlO₅ can be synthesis by using high temperature solid phase reaction method and sol-gel method.So,we can obtain novel phosphors by adjusting the microstructure around the luminescence centers.In present work,a systematic research was carried out on the processing methods,luminescence properties,spectral tuning of the rare earth doped LaSr₂AlO₅.Finally,we should be packing the phosphors for white LED.This paper main research content is as follows:?1?We successfully synthesized the LaSr₂AlO₅:Ce³⁺yellow phosphors and LaSr₂AlO₅:Eu²⁺red phosphors by the solid state reaction method,in the 1400?under N₂+H₂ atmosphere.We can determine the optimum synthetic process.The diffraction peaks of samples fit very well with the XRD pattern of LaSr₂AlO₅ without the presence of obvious impurity diffraction peaks,indicating that LaSr₂AlO₅ single crystal phase.The particle has a kind of spherical morphology and particle surface is smooth.?2?Luminescence properties of Eu²⁺doped LaSr₂AlO₅ were systematically investigated.When nano-Al₂O₃ is to be the raw materials for Eu²⁺doped LaSr₂AlO₅ phosphor,the intensity of samples increased 21.2%.The excitation bands of LaSr₂AlO₅:Eu²⁺cover the spectral region from UV to the visible part?250-480nm?,the emission spectra show a single intense board emission band centered at 610nm,which is ascribed to the allowed 4f⁶5d?4f⁷ transitions of Eu²⁺.The full width half maximum?FWHM?of LaSr₂AlO₅:Eu²⁺is 112nm.With increasing the concentration of Eu²⁺,concentration quenching of emission spectra were observed.So,Eu²⁺doped LaSr₂AlO₅ phosphors can be used to the white LED.?3?LaSr₂AlO₅:Sm³⁺phosphors were synthesized by the Pechini-type sol-gel process.The X-ray diffraction pattern revealed that a pure LaSr₂AlO₅ phase was obtained with a sintering temperature of1200°C.Microstructure characterization showed the particles are spherical in shape with a mean size of2.93?m.Being a candidate orange/red emitting phosphors for orange and white light emitting diodes,LaSr₂AlO₅:Sm³⁺can be effectively excited by both near-ultraviolet?NUV?and blue lights with typical f–f transitions of Sm³⁺ions.The most intense emission corresponding to ⁴G_5/2?⁶H_7/2?604nm?can be achieved at the same Sm³⁺concentration of 4mol%.The chromaticity coordinates of La_0.96Sr₂AlO₅:0.04Sm³⁺phosphor under the excitation of 407 nm and 458nm are?0.57,0.43?and?0.59,0.38?,respectively.Further study has been carried out using Van Uitert's and Dexter's models.A consistent result is obtained that electric dipole-dipole interaction is dominant for the energy transfer among Sm³⁺.The critical distance for energy transfer among Sm³⁺in LaSr₂AlO₅ is calculated to be ca.18.43?.?4?The excited state of the 5d electrons of rare-earth elements is significantly lowered to low energy due to large crystal-field splitting and a strong nephelauxetic effect.With the increasing of the content of Gd³⁺doped La_0.996-xGd_xSr₂AlO₅:0.004Bi³⁺phosphors have a red shift.When B³⁺to replace part of Al³⁺in the LaSr₂AlO₅,the phosphor emission spectrum peak have a red shift from 450nm to 465 nm.When z=0.15,the maximum emission peak intensity.With the increasing amount of SrF₂,the particle size of powders increases and the shape of particles changes more regularly.Being an orange/red emitting phosphors for orange and white light emitting diodes,LSAF:Ce³⁺can be effectively excited by blue lights with typical 4f?5d transitions of Ce³⁺ions.PL and PLE spectra show inhomogeneous enlargement effects with the increase of F/O ratios,which suggest that electronegativity effects is promoted when F/O ratio increases.This is further confirmed by a red shift of PL spectra peak when F/O is increased.It can be concluded that the LSAF:Ce phosphors have the potential to meet the development of white light-emitting diodes.?5?Packing the phosphor of LaSr₂AlO₅.The luminous efficacy of white LED lights is 43 lm/W,color coordinates is?0.4015,0.4015?,correlated color temperature is 3767 k and color rendering index is94.It catch the high color rendering index,low color temperature of white LED;By the technology of remote phosphor,choose LaSr₂AlO₅:Ce³⁺and LaSr₂AlO₅:Eu²⁺phosphor,along with the increase in number of spray,thickness of phosphor layer also gradually thickening,LED light-emitting device color from blue to cold white light to warm white;When the thickness of phosphor layer increased to 105 mm,quantum efficiency is 75%,luminous efficiency achieved 62 lm/W.At the same time,LaSr₂AlO₅phosphor has wide application prospect for white LED.