Preparation And Luminescence Mechanism Of Luminescent Materials For White-LEDs

White light emitting diodes(WLED)is a new type of solid-state lighting device,with the advantages of high luminous efficiency,energy saving,long life,non-polluting and so on.Because of its unique advantages,white LED will replace incandescent,fluorescent and other traditional lighting device.Phosphor is one of the key technologies of the white LED.Therefore,the development of new types of phosphor for WLED is worth in academic research and practical application prospects.The aim of this thesis is to design and synthesize the novel luminescent materials which possess high luminescence efficiency and stability for NUV LEDs.We prepared luminescent materials by high temperature solid-state reaction method and hydrothermal method.Crystal structure,morphology and luminescence properties of the phosphors were characterized by the modern analytical instruments of X-ray diffraction(XRD),Field Emission Scanning Electron Microscope(FESEM)and fluorescence spectroscopy,respectively.Their excitation spectra,emission spectra and energy transfer were also investigated in detail.The thesis consists of the following contents.Firstly,Eu2+ and Mn2+ co-doped SrMgB6O11 white glass samples was synthesized by sintering at 1100 ? for 2 h under a weak reduction gas atmosphere.The fluorescence spectrum shows that the emission spectrum of the luminescent glass has two bands,peaking at 457 nm and 645 nm.The excitation spectrum are distributed in the range of 250?400 nm.The resonant ED-ED energy transfer from Eu2+ to Mn2+ is shown to be effective.The influence of the doping concentration on the luminescence intensity and color coordinates was also investigated and optimized,which is close to the color coordinates(0.345,0.285)of white light.Afterwards,Eu3+ doped SrMgB6O11 nano-phosphors were prepared by hydrothermal method.The results of XRD indicated that diffraction peaks are sharp and strong when temperature is 120 ? and pH is 9,meanwhile the FESEM shows that the morphology is the fan-shaped by made of nanorods.The peaks of the emission between 500 nm and 700 nm are assigned to 5D1?7F1,5D0?7Fj(j = 0?4)transitions of Eu3+,and the peaks of exctition spectra are assigned to 7F0?5D4,7F0?5L8,7F0?5L6,7F0?5D2 transitions of Eu3+.Secondly,two series of phosphor BaSrMg(PO4)2:Eu2+,Mn2+ and BaSrMg(PO4)-(BO3):Eu2+,Mn2+ are prepared by high temperature solid-state reaction method.Photoluminescence of BaSrMg(PO4)2:Eu2+,Mn2+ shows that the excitation spectra are broad bands ranged from 250 to 430 nm.The emission spectra are ranged from 390 to 750 nm,and show white light emitting by coupling three bands with blue,yellow and red emission.Meanwhile,the addition of H3BO3 to the above phosphor results in broadening of the emission peak width and enhancing of the luminescence intensity.Correlated color temperature(Tc)and color rendering-index(Ra)are also improved with Tc = 3467 K and Ra = 92.6,respectively.The chromaticity coordinates is(0.334,0.350).Afterwards,red phosphor BaSrMg(PO4)2:Eu3+ was prepared by a hydrothermal method,and its crystal structure,morphology and luminescence properties were characterized.The results show that when temperature is 140? and pH is 6,the morphology of the red phosphor is the piled structure by made of rectangulars.The emission spectrum show that the phosphor with a strong red emission.