Synthesis And Luminescence Property Of Blue-emitting And Green-emitting Phosphor For PDP

Plasma flat panel display technology eliminates the geometric distortion of the picture, and offers brightness uniformity, high color purity, high contrast, and other advantages. Plasma flat panels (PDPs) is the most promising candidate for large size flat-panel information-display devices, is a very important development direction of HDTV. Fluorescent powders are one of the key factors which determine display quality. PDP phosphor is excited by147nm or172nm vuv light, therefore, it should have good thermal stability, high luminous efficiency, small powder particle size, and a narrow range of grain size distribution, high color purity, afterglow time is short and other properties. The performance of present commodities-PDP phosphor has many shortcomings:(l)red phosphor:color purity of (Y,Gd) BO3:Eu3+red phosphor is not high, and light-emitting efficiency of Y2O3:Eu3+is relatively low, and (2)blue phosphor: Eu2+activated BAM phosphor has poor stability, and its peak maximum also shift during various stages of panel fabrication and (3)green powder:the decay time of Zn2SiO4:Mn2+phosphor is somewhat longer for practical application.Therefore,(La,Ce,Tb) BO3green phosphor, Ln (BO3,PO4):Ce3+,Tb3+green phosphor, BAM:Eu2+blue phosphor for PDP are synthesized by high temperature solid state reaction and modified high temperature solid state reaction. SEM, XRD, TG-DTA, luminescence spectra and other means were used to study the phosphor samples. The effect of flux on high temperature solid state reaction mechanism and the feasibility of the spray pyrolysis synthesis using to synthesize rare earth luminescent materials were studied. The studied conclusions came following:(1) The phosphors of (La,Ce,Tb)BO3was synthesized by high temperature solid state reaction. X-ray diffractometry (XRD) patterns indicate that the Crystal Structure of (La,Ce,Tb)BO3and LaBO3is the same. The crystal structure has not been changed by Ce3+and Tb3+mixed into. Emission scanning electron microscopy (SEM) images show that the particle size of phosphors is more uniform, morphology is more rules, and granularity is about5μm. The content of TbBO3phase in (La,Ce,Tb)BO3increases with increasing of Tb content in (La,Ce,Tb)BO3. When Tb concentration reaches15%and above, the content of TbBO3phase in (La,Ce,Tb)BO3increases more rapidly. The luminescence properties of (La,Ce,Tb)BO3and the sensitization of Ce3+to Tb3+were studied. There are three peaks at around244,268and330nm in the excitation spectrum of Ce3+, and there are two peaks at365and380nm in the emission spectrum of Ce3+, respectively. All of them have the large overlap. The excitation peaks of Tb3+is230nm and its Maximum emission wavelength is541nm. Both the Tb3+characteristic emission and excitation peaks and the Ce3+characteristic emission and excitation peaks were observed in the emission and excitation spectrum of (La,Ce,Tb)BO3. Comparing the emission spectrum of (La,Tb)BO3with the excitation spectrum of (La,Ce)BO3, and find them having the large overlap, it inferred that there is remarkable energy transfer from Ce3+to Tb3+in it. When the concentration of Ce or Tb in (La,Ce,Tb)BO3is fixed, because of concentration self-quenching effect, the relative intensity of main emission peak (at541nm)increases firstly and then decreases with increasing of the concentration of Tb or Ce. At fixed ratio of Ce concentration to Tb concentration, the relative intensity of the main emission peak of (La,Ce,Tb)BO3is the highest when La concentration in (La,Ce,Tb)BO3reaches70%. The sample with better luminescence properties will be obtained in variety range of Ce concentration to Tb concentration at fixed La concentration of80%. When La concentration is80%and above, the relative intensity of the main emission peak of (La,Ce,Tb)BO3will be highest at Ce concentration to Tb concentration of3/1. Comparing commercial phosphor (La,Ce,Tb)PO4with experimental (La,Ce,Tb)BO3phosphor, experimental (La,Ce,Tb)BO3phosphor has a little red shift at489nm and its relative emission intensity was94.7%of the commercial phosphor (La,Ce,Tb)PO4. Therefore, it is inferred that (La,Ce,Tb)BO3would be a promising PDP green-emitting phosphor.(2) Cerium-and terbium-doped lanthanum borophosphate [Ln(BO3,PO4):Ce3+, Tb3+] phosphor have been prepared by a single-step calcination using self-made BPO4as borophosphate sourse. Fine crystal structures are observed by XRD patterns. The excitation spectrum of Ln(BO3,PO4):Ce3+,Tb3+(Ln=Y, La, Gd) includes host sensitization band at120-175nm which is relative to the BO33-and PO43-groups, and several bands at175-300nm originated from4fâ†'5d transition of Tb3+. The replacement of the host leads to changes of fluorescence Intensity ratios and CIE coordinate in emission spectrum. Among these phosphors, Gd(BO3,PO4):Ce3+,Tb3+phosphor shows best green fluorescence intensity ratio. The lifetime of the emission transition3D4â†'7F4of Tb3+is2.92ms, with a10%afterglow of6.7ms, which make it better than Zn2SiO4:Mn2+commercial phosphor for PDP.(3) BaMgAl10O17:Eu2+phosphors were synthesized by high temperature solid-state reaction method. Using the X-ray powder diffraction, scanning electron microscopy and photoluminescence spectra, the effect of different fluxes, reaction time on such properties as crystals crystallinity, phase purity, particle morphology, luminescence intensity and thermally stability of the blue phosphor were investigated. The mechanism of synthesis of BaMgAl10O17:Eu2+with different fluxes was analyzed. The results show that synthesis conditions such as flux, concentration of doped ions, sintering temperature and time, reduction temperature and time have important influence on crystals crystallinity, phase purity, particle morphology, luminescence intensity and thermally stability of the blue phosphor. Incorporation of Sr has little influence on crystal structure of BAM matrix, it would cause the drop of initial relative brightness of phosphor’s, but the thermally stability of BAM luminous phosphor would be improved. When flux is adopted, BaMgAl10O17:Eu2+phosphors with more regular morphology, uniform particle size and crystals crystallinity can be obtained at lower sintering temperature. Incorporation of Eu2+has less influence on crystal structure of BaMgAl10O17matrix. Along with the agglutination time’s extension, the sample’s crystallization becomes more completely, the content of impurity phase in it reduces and its luminous intensity increase. As different fluxes are used, the mechanism of synthesis of BaMgAl10O17:Eu2+will change. The performances of prepared sample such as crystallization integrity, phase purity, the luminescent center distribution have corresponding change with the change of the synthesis mechanism, thus the luminescent properties of the samples change correspondingly.Comparing the experimental blue phosphor obtained at optimized conditions (Ba0.82Sr0.08MgAl10O17:Eu0.1) with the commodity powder BAM, relative emission intensity of the experimental blue phosphor is98.3%of the commercial phosphor BAM, its color coordinate is close to the commercial phosphor (experimental blue phosphor’s color coordinate is x=0.0145, y=0.072, and the color coordinate of commercial phosphor is x=0.0145, y=0.072). The experimental blue phosphor has better thermally stability than that of the commercial phosphor. The granularity of it was3.24μm Therefore, it is expected that the experimental blue phosphor would be used for PDP blue phosphor.(4) Through the synthesis of SrAl2O4:Eu,Dy, the feasibility of the spray pyrolysis synthesis using to synthesize rare earth luminescent materials was studied. Experimental results show that spray pyrolysis method is a desirable method of synthesis of rare earth luminescence materials as long as the technology conditions are optimized. Compared with the SrAl2O4:Eu,Dy prepared by solid state method, the SrAl2O4:Eu,Dy prepared by spray pyrolysis has more regular morphology (compact solid spherical particles), smaller particle size, narrower particle size distribution and more excellent luminescent properties, and the synthesis temperature can be significantly reduced.The SrAl2O4:Eu,Dy prepared by spray pyrolysis belongs to the α-SrAl2O4phosphor crystal structure and small amount of Eu, Dy doped into the matrix has little effect on the crystal structure of SrAl2O4. The morphology, size distribution and luminous performances of the phosphors could be affected with synthesizing conditions, such as precursor concentration, sintering temperature, reduction temperature etc. As the reduction temperature rised, red shift of the main peak position in the emission spectrum occurs (move to longer wavelengths).Additives caould obviously improve the morphology, reinforce the initial brightness, and enlarge the afterlow time (citric acid would shorten the afterlow time). Citric acid could help to obtain solid spherical particle. Ethanol was not only a good dispersant but also improved the sphericity of particle. Howerve, solid spherical particles couldn’t be gotten in this condition. PEG played the role of dispersant and stabilizer. The solid spherical SrAl2O4:Eu,Dy particles with high initial brightness, long twilight time, good dispersion, small particle size and narrow particle size distribution (2μm～5μm) when these additives was used at the same time.