Preparation,Structure Analysis And Luminescence Properties Of Garnet Phosphor For White LED

White LED possess the advantages of long lifetime,high luminous efficiency,energy saving and environmental friendly,which make it become the fourth generation of lighting systems to substitute the traditional incandescent and fluorescent.Phosphor is an important part of white LED,and the development of new phosphor is of great significance to achieve high colour rending index.The main purpose of this thesis is to improve the properties of garnet phosphor by cation substitution to get new garnet structure phosphor.X-ray Diffraction?XRD?,Scanning Electron Microscopy?SEM?,Transmission Electron Microscopy?TEM?,X-ray Photoelectron Spectroscopy?XPS?and photoluminescence excitation and emission were used to characterize the properties of the phosphor.The main contents are described as follows:1 A series of different concentration of Ce³⁺-doped Mg₂Y₂Si₂Al₂O₁₂is designed for the aim of a large distortion of the dodecahedron and an external pressure from the large octahedron through combination substitution of both dodecahedral Y³⁺and octahedral Al³⁺sites with Mg²⁺.The garnet structure and elemental composition of this phosphor were confirmed by XRD,SEM and TEM.The particular coordination environment of each element of the phosphor was illustrated by XPS and Rietveld refinement.Mg₂Y_1.94Al₂Si₂O₁₂:0.06Ce³⁺exhibits a strong and broad yellow-orange emission band with the peak at 600 nm,Comparing with the commercial phosphor YAG:Ce³⁺.This red-shift could be mainly ascribed to the distortion and shrinking of dodecahedron and subsequently the larger crystal field splitting of the Ce³⁺5d levels.White LED was fabricated and shows high colour rending index up to 84.In comparison with YAG:Ce³⁺,the properties are improved.2 To develop a new garnet phosphor with redshift of Ce³⁺emission and get insight into its underlying factors,an overall compression environment with anisotropic expansion for the activator ion Ce³⁺was designed by the strategy of incorporation small cation Mg²⁺into the dodecahedral Y³⁺site.The successful substitution of Mg²⁺in dodecahedral Y³⁺site in the novel garnet phosphor MgY₂Al₄SiO₁₂:Ce³⁺was achieved,which was confirmed by the Rietveld refinements of XRD data,TEM and XPS results.The emission of MgY_1.94Al₄SiO₁₂:0.06Ce³⁺ranges from 500 nm to 750 nm with the maximum at 560 nm,which means the expected redshift is realized,comparing with the commercial phosphor YAG:Ce³⁺?542 nm?.Furthermore,the static stronger crystal field splitting factor is found to be not comprehensive for understanding such redshift,while the dynamic aspect factor of bigger Stokes shift works for this interpretation,based on the difference bond length changing and the crystal field splitting data versus the counter phosphors Y₃Al₃MgSiO₁₂:Ce³⁺and YAG:Ce³⁺.Fabricating the phosphor with 460nm blue LED,we can obtain the color coordinates?0.3302,0.3583?which is close to the white lighting?0.333,0.333?.