Investigation On Fabrication And Performance Of White LED Pattern Phosphor Coating

The light-emitting diode(LED)has gained widespread popularity in its applications to residential illumination while offering the advantages of energy saving,environment sustainability,and long lifetimes.Stimulating the phosphor with blue chip is the most important method to manufacture the white LED.Additionally,the phosphor coating is often composed of a variety of phosphors for enhancing the optical quality of white LED.Nevertheless,the red nitride phosphor powder has a serious reabsorption effect on the yellow and green fluorescence in the phosphor coating directly mixed with different kinds of phosphors,which would deteriorate the LED light efficiency.The reported study on reducing the reabsorption in white LED focused on the vertical or horizontal direction segmentation of the whole phosphor coating,without considering the chip position and light intensity distribution of the corresponding parameter matching study.In this paper,the design and preparation method of white LED pattern phosphor coating is proposed to reduce the re-absorption of phosphor and improve the efficiency and optical quality of white LED.The main contents are as follows:(1)Design of the white LED pattern phosphor coating.Different phosphor coating in the plane is designed to take places in the regional way.The contact area of different phosphors and reabsorption then would be reduced.Combining with the excitation and scattering characteristics of the phosphor,the optimized design of the location,size and height of the white fluorescent LED coating is provided by Tracepro,which provides the direction for the preparation of the fluorescent coating;(2)Fabrication of the white LED pattern phosphor coating.Based on the design of the patterned phosphor coating,pulse spraying method and steel mesh mask were used for the precise phosphor coating.By optimizing the colloid concentration,spraying height,pulse timing,spraying distance and spraying velocity,the white LED devices with coating surface of good quality and uniform coating thickness were fabricated;(3)Investigation of the white LED pattern phosphor coating.The advantages of patterned coating devices versus conventional dispensing and directmixing remote-coating devices in light extraction efficiency,color rendering index,and color temperature were tested experimentally.Furthermore,the position,area and height of the patterned coating were optimized experimentally.Pattern coating and chip light intensity distribution were matched to developed white LED with high optical quality and efficiency;(4)Development of correlated-color-temperature-tunable white LED lighting system.The pattern coating process was applied to manufacture the color temperature tunable LED,in which phosphors colloid of different color temperature were coated on different areas of the COB(Chip On Board).By adjusting the light intensity ratio in different areas,the color temperature of the lighting system can be adjusted continuously from 2700 K to 6500 K.Then a microstructure array(MSA)film was applied to improve the angular color uniformity(ACU)of a correlated-color-temperature-tunable white LED.