Synthesis and Characterization of Highly Disperse Nano-YAG Phosphors

Author:Song Li

Supervisor:jiang jian qing


Degree Year:2018





Yttrium aluminum garnet(Y3Al5O12)doped with Ce3+ions(YAG:Ce)is commonly used in white light-emitting diodes(LEDs).Its luminous efficiency,spectral characteristics and particle size have important effects on the light efficiency,light color and light color uniformity of white LEDs.Highly dispersed nano-sized YAG:Ce3+phosphor particles can not only improve the spectral performance of white LEDs,eliminate the loss of light efficiency due to light scattering,but also can basically solve the problem of color temperature drift caused by phosphor settlement.If the size of the particles is reduced to less than 10 nm,the nano YAG:Ce is expected to become a new type of fluorescent probe,which can be applied in the life-science field.However,preparing highly dispersed nano-sized YAG:Ce phosphors is difficult because the agglomeration and sintering of nanoparticles during high-temperature(1000℃)synthesis are very serious.This study introduces water-soluble inorganic salts as high-temperature isolation medium,and successfully avoided agglomeration and sintering of YAG nanoparticles during high-temperature synthesis.Finally,a highly dispersed YAG phosphor particle with a particle size of only 5-6 nm was prepared.The particles have good crystallinity and exhibit good spectral characteristics and photostability.This paper first prepared nano-YAG precursor particles using urea precipitation method.Then use molten salt and high melting point solid salt as the isolation phase.The preparation technology of high-dispersion YAG particles was explored.The effect of precursor isolation mechanism and influence factors on the size and morphology of nano-YAG particles was studied.The research process and conclusions are as follows:First,the Al2O3 precursor was used as the object to study the precipitation reaction mechanism and various influencing factors.Then based on the optimization of the urea precipitation method parameters,a highly dispersed nano-YAG precursor particle was prepared with a particle size of 5-6 nm.Studies have shown that the suitable precipitation temperature is 85℃-90℃,and the precipitation time should not exceed 80 minutes.In this paper,YAG precursor particles and inorganic salt particles are mixed,and the dispersed nano-YAG particles are prepared by wetting and isolating the molten salt under a high temperature.The effects of molten salt species on the morphology and dispersity of YAG particles were discussed.The influence of the size of molten salt on the morphology,dispersivity and luminescence properties of YAG particles was studied.Finally,a highly crystalline nano-YAG phosphor with good crystallinity was obtained.The particle size is about 200 nm and the internal quantum efficiency is about 93%.It was found that the dispersion of the precursor particles on the surface of the raw salt particles is a key factor in regulating the size and dispersibility of the nano-YAG particles.This article originally developed a salt microemulsion method for the preparation of highly dispersed nanoparticles.The study found that uniform and highly dispersed nanoα-Al2O3 particles below 10 nm can be prepared at 1000℃ by using cyclohexane-CO-520 as the microemulsion system and K2SO4 as the isolation salt.By adjusting the precursor particle size and salt ratio,the size ofα-Al2O3 particles can be controlled to a certain extent.It is considered that in the salt-containing microemulsion,the aqueous phase is dispersed in the oil phase as nanometer water droplets,and the nano-droplets consist of precursor particles and salt solution.The precursor particles are coated and isolated by the potassium sulfate nanoparticles during demulsification.In the subsequent high temperature process,the salt particles always isolate the precursor or product particles.This paper also tried to prepare the Eu3+ion-doped nano-α-Al2O3:Eu3+phosphor.Based on the preparation ofα-Al2O3 particles by salt-containing microemulsion method,two kinds of microemulsion systems,cyclohexane-CO-520 and cyclohexane-triton,were tried.Obtained 5 nm and 20 nm highly dispersed YAG phosphor particles,respectively.The study found that,by changing the precursor morphology and salt ratio,the morphology and size of nanoparticles can be regulated to a certain extent.On the basis of stable preparation of highly dispersed nano-YAG phosphors,the emission spectrum,excitation spectrum,quenching concentration of activation ion and photostability were studied.The study found that:(1)Compared with micro-sized YAG:Ce phosphors,the emission spectrum of nano-YAG:Ce particles has a certain red shift,and its emission spectrum has a broadening phenomenon.The reduction of particle size not only affects the field strength of YAG crystal and the Stokes shift of Ce3+,but also decreases the energy level interval between the ground state level and the top of the matrix valence band of Ce3+;(2)Particle size change does not affect the quenching concentration of Ce3+ions in YAG crystals.(3)High-dispersion YAG phosphors prepared at a high temperature of 1000℃ have good photostability,and after 48h of 450-nm blue light the emission intensity was reduced by only approximately 16%.