In 1993, Shuji Nakamura, who worked at Nichia Corporation in Japan, invented commercially available blue light based on wide bandgap semiconductor materials gallium nitride (GaN) and indium nitride (InGaN) LED, this type of LED in the late 1990s have been widely used. In theory, Blu-ray LED combined with the original red LED and green LED can produce white, but the white LED is rarely made out of this way.
Most of the white LEDs currently produced are made by covering a layer of pale yellow phosphor coating on a blue LED (near-UV, wavelengths from 450 nm to 470 nm), which is usually obtained by mixing cerium doped with cerium Aluminum garnet (Ce3 +: YAG) crystals are ground into powder and mixed in a dense adhesive. When the LED chip is blue, part of the blue light will be this crystal is very efficient conversion into a broad spectrum (spectral center is about 580nm) mainly yellow light. (In fact, the monocrystalline Ce-doped YAG is treated as a scintillator than the phosphor.) Since the yellow light stimulates the red and green receptors in the naked eye and then blends the blue light of the LED itself, it looks like white light , And its color is often called "moonlight white". This method of making white LEDs was developed by Nichia Corporation and has been used in the production of white LEDs since 1996. To adjust the color of light yellow light, other rare earth metal terbium or gadolinium can be used to replace cerium (Ce) doped in Ce3 +: YAG, or even to replace part or all of aluminum in YAG