Study On Surface Modification Of YAG:Ce³⁺ Phosphor Powder Using For LED

Surface modification can be done by certain methods in order to improve the physical or chemical properties of the surface of the powder, such as surface structure, surface energy, surface wettability, electrical property, adsorbability and so on. This modification can fulfil the needs of development of new material and technology in modern society.Phosphor is one of the key material in the LED device. Its properties directly affect the brightness, chromaticity coordinates, chromatic temperature, color rendering property and so on. Uncoated phosphor powders are agglomerate and not stable in electrical and chemical properties because of extrinsic and intrinsic factors. This can lead to low temperature of fluorescence quenching, nonhomogeneity in luminescence and so no. So it is necessary to find a new method to improve the stability of the phosphor. Surface coating is an good method, which can improve the agglomeration, corrosion resistance and thermal degradation properties of powders through coating a layer of thin film. That even can improve the intension and tenaciousness of powder.In this paper,the modification of YAG:Ce³⁺ phosphor powders were studied by the surface coating technology to solve the problem of thermal degradation during the using of LED. The silicon dioxide was chose as coating material according to its excellent physical and chemical properties. The sol method was used to coat the YAG:Ce³⁺ phosphor with TEOS as silicon reagent. The influence of coating time, coating temperature, pH of the catalyst, sintering temperature and time, and the amount of SiO₂ to the effect of coating was studied. The phase composition, microstructure and luminescence properties of the powders coated were characterized by SEM, XRD, TEM and FS. The XRD analysis showed that crystal phase composition after coating is the same with that uncoated powders. The process did not introduce other component. The TEM images indicated that a compact homogeneous film which was confirmed as SiO₂ film by energy spectrum analysis was coated on the surface of YAG:Ce³⁺ phosphor particles successfully. And the fluorescence spectrum showed that not only the luminescence properties of the YAG:Ce³⁺ phosphor was not affected by the film, but also the thermal degradation property was improved obviously by the coating process.