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Semiconductor LED principle
With the formation of GaN blue LED1993 years, at that time in Japan NichiaCorporation (Nichia chemical) work of Nakamura Shuji (ShujiNakamura) invented the wide band gap semiconductor materials based on gallium nitride (GaN) and gallium indium nitride (InGaN) has the commercial value of the blue LED, this kind of LED has been widely used in the late 1990's. Theory combined with the original red blue LED LED and green LED can produce white, but white LED but this is rarely made.
White LED is currently produced by most in blue LED (wavelength near-UV, 450nm to 470nm) is covered with a layer of pale yellow fluorescent powder coating made of yellow phosphor, this is usually done by mixing cerium YttriumAlum
Light emitting diode
InumGarnet (Ce3+: YAG) crystal ground into a powder mixed in a dense adhesive made. When the LED chip to emit blue light, part of the blue light will be the crystal is efficiently converted into a wide spectrum (spectral center is about 580nm) is mainly for the Yellow light. (Ce doped single crystal YAG actually is seen as more than a phosphor scintillator. ) because of yellow light stimulates the eye red light and green light receptor, then mixed with LED itself to make it look like a blue light, white light, and the color is often referred to as the "Moonlight white". This method of production of white LED is made by NichiaCorporation and from the beginning of 1996 used in the production of white light LED. To adjust the yellowish light color, the availability of its rare earth metal terbium or GD substituted Ce3+: YAG doped with cerium (Ce), and even can do to replace the YAG in all or part of the aluminum way. Based on the spectrum characteristics, the red and green object in this kind of LED irradiation would look less Kuopu light source is so bright.
In addition, due to the variability of production conditions, the yield of LED color temperature is not uniform, from the warm yellow to blue are cold, so in the production process will be based on the characteristics of out make a distinction.
Method for white light LED another production is a bit like a fluorescent light, emitted near UV LED will be a mixture of two kinds of phosphors coated on the hair, is a red and blue of the EU, the other one is green, doped zinc sulfide (ZnS) of copper and aluminum. But because ultraviolet rays will make epoxy resin adhesive cracking metamorphism in production, so the higher difficulty, and the service life is short. Compared with the first method, it has low efficiency and produce more heat (because StokesShift is larger), but the benefits are spectral properties of light generated by a better, more good-looking. Because LED high power UV, so its efficiency is compared to the first method is low, out of the brightness is comparable to.
Methods the latest manufacturing a white light LED didn't use the phosphor. The new approach is in ZnSe (ZnSe) substrate epitaxial layer growth of znse. When the power is switched on the active zone will issue a blu ray and substrate will send the yellow light, mixed up is white light.
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