Study On Synthesis And Properties Of Phosphors For White LEDs By Using Submicron Spherical SiO₂ Particles As Percursors

The size ditribution and the shape of phosphor particles affect the efficiency of w-LEDs, thus it is important to controll the size and the shape of the phosphor particles used for w-LEDs. In order to research the influence of the precursors and the synthesis method on the shape, size and luminescent properties of phosphor particles, mono-disperse SiO₂ micro-spheres prepared by the St?ber method were used as precursors to get three kinds of phosphors. And the properties of these phosphors have been compared with those prepared by the traditional solid state method.First, submicron spherical SiO₂ particles have been coated with AgEu(MoO₄)₂ phosphor layers by a sol-gel process, to get core-shell structured SiO₂@AgEu(MoO₄)₂ particles. The test results about the structure, shape and composition of the phosphors indicate that AgEu(MoO₄)₂ has been crystallized on the surface of SiO₂ particles forming the core-shell structured SiO₂@AgEu(MoO₄)₂ particles. The photoluminescence (PL) spectra of the core-shell structured phosphors are similar to the pure AgEu(MoO₄)₂ phosphors prepared by the same sol-gel method and they both exhibit red emission. The PL intensity of the core-shell structured phosphors could be tuned by changing the coatings times.Second, Sr2SiO₄: Eu²⁺ phosphors were prepared by a modified sol-gel method by using SiO₂ micro-spheres as precursors. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to characterize the shape of phosphor particles. One-dimensional Sr2SiO₄:Eu²⁺ nanorods were obtained by this method, which show intense blue-green emission under the excitation of near ultraviolet light (n-UV, 275-425 nm). The result indicates that Sr2SiO₄:Eu²⁺ phosphors are promising blue-green candidates for the n-UV white LEDs.Finally, BaSiO₃ host phosphor particles with narrow size distribution and regular shape were synthesized by the sol-gel method using SiO₂ micro-spheres as precursors. A series of different color phosphors is achieved by doping Ce³⁺ and Eu²⁺ in the host and the energy transferring from Ce³⁺ to Eu²⁺. The CIE chromaticity coordinates of BaSiO₃:Ce³⁺, Eu²⁺ have been figured out based on the photo-luminescent spectra of phosphors. When Ce³⁺ concentration is 2.5% and Eu²⁺ concentration is 2%, this phosphor generates white emission.