1998 white LED has been successfully developed. This kind of LED is encapsulated by GaN chip and yttrium aluminum garnet (YAG). GaN chip emits blue light (λp=465nm, Wd=30nm), and the high-temperature sintered YAG phosphor containing Ce3+ emits yellow light after being excited by this blue light, with a peak value of 550nm. The blue LED substrate is installed in the bowl-shaped reflection cavity and covered with a thin layer of YAG-mixed resin, 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 YAG phosphor and adjusting the thickness of phosphor layer, various white lights of 3500- 10000K can be obtained.

The luminous color and luminous efficiency of LED are related to the material and manufacturing process of LED. Red, green and blue are widely used at present. As the working voltage of LED is low (only 1.5-3V), it can actively emit light with a certain brightness, and the brightness can be adjusted by voltage (or current), so it is shock-resistant and vibration-resistant, and has a long service life (65438+100000 hours). Different materials of LED can produce photons with different energies, so the wavelength of light emitted by LED, i.e. spectrum or color, can be controlled. The material used for the first LED in history is gallium arsenide (As) (Ga), and its forward PN junction voltage drop (VF, which can be understood as lighting or working voltage) is 1.424V, and the light emitted is infrared spectrum. Another commonly used LED material is gallium phosphide (Ga), whose forward PN junction voltage drop is 2.26 1V, and the light emitted is green. Based on these two materials, the early LED industry used GaAs 1-xPx structure, which can theoretically produce LEDs with any wavelength from infrared light to green light, and the subscript x represents the percentage of phosphorus replacing arsenic. Generally, the wavelength color of LED can be determined by the voltage drop of PN junction. Typical ones are the red led of GaAs0.6P0.4, the orange led of GaAs0.35P0.65 and the yellow led of GaAs0. 14P0.86. Because gallium, arsenic and phosphorus are used in the manufacture, these LEDs are commonly known as ternary LEDs. The blue led of GaN, the green LED of GaP and the infrared LED of GaAs are called binary LEDs. At present, the latest manufacturing process is a quaternary LED made of four elements: aluminum (Al), calcium (Ca), indium (In) and nitrogen (N), which can cover all the spectral ranges of visible light and part of ultraviolet light.

So it is the material and current that make LED that determine the light wave that emits light.