Development of white LED
For general lighting, people need white light source more. In 1998, white LED was successfully developed. This led is made of Gan chip and yttrium aluminum garnet (YAG). Gan chip emitting blue light（ λ P = 465nm, WD = 30nm), the YAG phosphor containing Ce3 + Prepared by high-temperature sintering emits yellow light after being excited by this blue light, with a peak of 550nm. The blue LED substrate is installed in the bowl shaped reflecting cavity and covered with a thin layer of resin mixed with YAG, about 200-500 nm. 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 LEDs, various colors of white light with color temperature of 3500-10000k can be obtained by changing the chemical composition of YAG phosphor and adjusting the thickness of phosphor layer.
Table 1 lists the types of white LEDs and their luminous principles. At present, the first commercialized product is blue light single crystal chip plus YAG yellow phosphor. Its best luminous efficiency is about 25 lumens / watt. YAG is mostly imported by Japan’s Riya company, and the price is 2000 yuan / kg; The second is that Sumitomo Electric also developed white LED with ZnSe as material, but the luminous efficiency is poor.
It can also be seen from the table that some kinds of white LED light sources are inseparable from four phosphors: three primary color rare earth red, green, blue powder and garnet structure yellow powder. In the future, three wavelength light is more promising, that is, inorganic ultraviolet chip plus r.g.b three color phosphor is used to package LED white light. It is expected that three wavelength white LED will have commercialization opportunities this year. However, the particle size requirements of trichromatic phosphors here are relatively small and the stability requirements are also high. The specific application is still being explored.
Luminescence principle of chip digital excitation source luminescent materials
1. The blue light of blue ledingan / yagingan is mixed with the yellow light of YAG to form white light
Blue ledingan / phosphor InGaN Blue excited red, green and blue phosphors emit white light
The blue ledznse is mixed with the blue light emitted by the thin film layer and the yellow light excited on the substrate to form white light
UV ledingan / phosphor InGaN the UV excited red green blue trichromatic phosphor emits white light
2 blue ledingan and gap package the two chips with complementary color relationship together to form a white LED
Yellow green LED
3 blue ledingan
AlInGaP encapsulates three small pieces of hair in three primary colors to form a white LED
Multiple ledingan and gap with multiple light colors package a variety of optical chips throughout the visible region to form a white LED
Using LED light source for lighting, first replace the power consuming incandescent lamp, and then gradually enter the whole lighting market, which will save a lot of electric energy. Recently, the white LED has reached a single power consumption of more than 1 watt and light output of 25 lumens, which also increases its practicability.
Among the LED industry, Nichia chemical is the first to use the above technology to develop high brightness LEDs with different wavelengths and blue violet semiconductor laser (LD). It is a heavyweight industry holding the patent right of blue LED in the industry. After Riya chemical obtained many basic patents such as blue LED production and electrode structure, it insisted on not providing external authorization and only adopted its own production strategy in order to monopolize the market, making the price of blue LED high. However, other manufacturers with production capacity are quite dissatisfied. Some Japanese LED manufacturers believe that the strategy of Nichia chemical will gradually be preempted by LED manufacturers in Europe, America and other countries in the competition of blue and white LED, which will cause serious harm to the overall Japanese LED industry. Therefore, many manufacturers will try their best to carry out the R & D and production of blue LED. At present, in addition to Nichia chemical and Sumitomo Electric, Toyota synthetic, Luomu, Toshiba and sharp, American Cree, three major lighting plants in the world, singular, Philips, OSRAM, HP, Siemens, research and Emcore have invested in the R & D and production of this product, which has played a positive role in promoting the industrialization and marketization of white LED products.
Source; International LED network