Development and design of white light LED

Development and design of white light LED

In 1998, white light LED was successfully developed. This LED is made by packaging GaN chip and yttrium aluminum garnet (YAG) together. GaN chip emits blue light (λp=465nm, Wd=30nm), and the YAG phosphor containing Ce3+ made by high temperature sintering is excited by this blue light and emits yellow light with a peak value of 550nm. The blue light LED substrate is installed in a bowl-shaped reflective cavity and covered with a thin layer of resin mixed with YAG, about 200-500nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LED, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, various colors of white light with a color temperature of 3500-10000K can be obtained. (As shown in the figure below)

Table 1 lists the types of white LEDs and their light-emitting principles. The first product that has been commercialized is a blue light single chip with YAG yellow phosphor. Its best luminous efficiency is about 25 lumens/watt. YAG is mostly imported from Japan's Nichia Company and costs 2,000 yuan/kg. The second is a white light LED developed by Japan's Sumitomo Electric Industries with ZnSe as the material, but the luminous efficiency is poor.
It can also be seen from the table that some types of white LED light sources cannot do without four types of phosphors: the three primary colors of rare earth red, green, and blue powder and the yellow powder of garnet structure. In the future, the three-wavelength light is more promising, that is, inorganic ultraviolet light chips plus RGB three-color phosphors are used to package LED white light. It is expected that the three-wavelength white light LED will have a chance to be commercialized this year. However, the particle size requirements of the three primary colors of phosphors here are relatively small, and the stability requirements are also high. The specific application is still under exploration. Using
LED light sources for lighting, first replacing power-consuming incandescent lamps, and then gradually entering the entire lighting market, will save a lot of electricity. Recently, white LEDs have reached a single power consumption of more than 1 watt and a light output of 25 lumens, which has also increased its practicality. Tables 2 and 3 list the performance progress of white LEDs. Table 2 Performance progress of single white LEDs

Table 3 Long-term development goals