In 1996, Nichia Chemical Co., Ltd. published a single-chip white LED with InGaN/Y3Al5O12:Ce3+ (YAG:Ce) phosphor. Since then, the world has been enthusiastically launching a competition for white LED related technology research and development. Compared with the way of using RGB tri-color LEDs to achieve white light, this single-chip blue LED with yellow (green and / or red) phosphor to achieve white light conversion technology solution avoids the complex design of multiple sets of control circuits, and low cost At the same time, the problem of light color drift caused by different decay speeds of the chip can be avoided, and the wide spectral coverage of the phosphor is beneficial to enriching the light and color characteristics of the target product. Therefore, the phosphor-converted white LED technology has quickly gained market acceptance and become the mainstream.
There are currently two mainstream phosphor coating methods for white LED packaging: traditional dispensing and conformal coating. However, the spatial color uniformity of the white LED products packaged by them, especially the cold white LED products, is not ideal, and there will be obvious yellow circle phenomenon (as shown in Figure 1), which greatly affects the quality of the packaged products and consumers. Feelings.
There are two reasons for the generation of the yellow circle problem: First, the distribution of the luminous intensity of the blue LED chip itself is not uniform in space. Figure 2 shows the near-field light distribution image on the surface of the blue chip. It can be seen from the figure that the blue light intensity distribution on the surface of the chip shows the characteristics of the regional distribution. The blue light intensity value in the central region of the chip is large, from the central area to the periphery. Expanded, the blue light intensity value shows a gradual decrease trend; secondly, the commercial phosphor powder currently used has a particle size of 10-15 μm. If the conventional dispensing method is used to coat the phosphor, the large particle size in the dispensing and baking process The phosphor is prone to sedimentation problems, which causes redistribution of the position of the phosphor particles, which also causes the spatial color uniformity of the white LEDs to deteriorate after encapsulation. By adopting the conformal coating method, the probability of redistribution of the phosphor can be reduced, but the blue light having a larger intensity value has a shorter distance from the phosphor layer in the central region than the phosphor layer passing through the edge region, and thus still causes the color temperature in the central region. The value is high and the color temperature value in the edge region is low (see Figure 3), resulting in a distinct yellow circle.
The Hong Kong Institute of Applied Science and Technology (ASTRI) has developed a phosphor processing technology that can process large-diameter phosphors into nano-sized phosphors with high luminous efficiency and good dispersion characteristics. About 300 nm, Figure 4 shows the particle size distribution of the nano-phosphor. The use of the nano-phosphor of the particle size range for LED encapsulation by conventional dispensing method can effectively alleviate the sedimentation problem of the phosphor during the packaging process, and the position of the phosphor remains unchanged during the dispensing and baking process. It can significantly solve the problem of poor color uniformity of white LED products, and obtain LED package products without yellow spots.
Unfinished
For more information, please refer to the February issue of Gaogong LED 's " LED Good Products" magazine.
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Halogen tube is a sealed light-emitting tube, filled with halogen element inert gas, the middle of the tungsten wire white, black two (due to the cost of white tungsten wire is much higher than the black tungsten wire, so the market is not universal ). Halogen tube with high thermal efficiency, heating is not oxidation, long life and other advantages, and some models also attached to the timing, rotation, humidification and other functions. Halogen tube heater is to rely on luminous heat dissipation, the general use of 2 to 3 halogen tube for the heat source, the power consumption of 900 ~ 1200W or so, more suitable for the area of about 12 square meters of the room, some of the more advanced products with automatic Power, automatic shaking his head and other functions, simple and practical design.
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