LED is a solid-state semiconductor device that can conv […]
LED is a solid-state semiconductor device that can convert electric energy into visible light. It can directly convert electric energy into light. The heart of LED is a semiconductor chip. One end of the chip is attached to a bracket, the other end is negative, and the other end is connected to the positive of the power supply, so that the whole chip is encapsulated by epoxy resin.
The semiconductor chip is composed of two parts, one is p-type semiconductor, in which the hole is dominant, the other is n-type semiconductor, in which the electron is mainly. But when the two semiconductors are connected, a p-n junction is formed between them. When the current acts on the chip through the wire, the electron will be pushed to the P area, where the electron and the hole compound, and then the energy will be emitted in the form of photons, which is the principle of LED luminescence. The wavelength of light, the color of light, is determined by the material that forms the p-n junction.
At first, led was used as the indicator light source of instruments and meters. Later, led with various light colors was widely used in traffic lights and large area display screens, which produced good economic and social benefits. Take the 12 inch red traffic light as an example. In the United States, the 140 watt incandescent lamp with long life and low light efficiency was originally used as the light source. It produces 2000 lumens of white light. After the red filter, the light loss is 90%, only 200 lumens of red light are left. In the newly designed lamp, Lumileds uses 18 red LED light sources, including circuit loss, which consumes 14 watts of power, producing the same light effect. Automobile signal lamp is also an important field of LED light source application.
For general lighting, people need more white light source. In 1998, white LED was successfully developed. This led is made of Gan chip and yttrium aluminum garnet (YAG) package. The Gan chip emits blue light (λ P = 465nm, WD = 30nm), and the YAG phosphor with Ce3 + produced by high-temperature sintering is excited by the blue light and emits yellow light with a peak value of 550nm. The blue LED substrate is installed in a bowl shaped reflecting cavity, 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 is mixed with the yellow light emitted by the phosphor to get white light. Now, for InGaN / YAG white LED, by changing the chemical composition of YAG phosphor and adjusting the thickness of phosphor layer, we can obtain all kinds of white light with color temperature of 3500-10000k. This method of getting white light through blue LED has the advantages of simple structure, low cost and high technology maturity, so it is widely used.