(Light Emitting Diode), a light-emitting diode, is a solid-state semiconductor device that can convert electrical energy into visible light. It can directly convert electricity into light. The heart of LED is a semiconductor chip,
One end of the chip is attached to a bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply, so that the entire chip is encapsulated by epoxy resin. The semiconductor wafer is composed of two parts. One part is a P-type semiconductor, in which holes are dominant, and the other end is an N-type semiconductor, where mainly electrons. But when these two semiconductors are connected, a P-N junction is formed between them. When electric current acts on the chip through the wire, the electrons will be pushed to the P region, where the electrons recombine with holes, and then emit energy in the form of photons. This is the principle of LED light emission. The wavelength of light, which is the color of light, is determined by the material that forms the P-N junction. Initially, LEDs were used as indicator light sources for instrumentation. Later, LEDs of various light colors were widely used in traffic lights and large-area display screens, resulting in good economic and social benefits. Take the 12-inch red traffic signal as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source. It produces 2000 lumens of white light. After passing through the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, 18 red LED light sources are used. Including the circuit loss, the total power consumption is 14 watts, which can produce the same light effect. Automotive signal lights are also an important field of LED light source applications.
For general lighting, people even need white light sources. In 1998, white LEDs were successfully developed. This LED is made by encapsulating a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp = 465nm, Wd = 30nm). The Ce3 + -containing YAG phosphor produced by high-temperature sintering emits yellow light after being excited by this blue light, with a peak value of 550nm. The blue LED substrate is installed in a bowl-shaped reflective cavity, covered with a thin layer of resin mixed with YAG, about 200-500nm. The blue light emitted by the LED substrate is partially 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. This method of obtaining white light through a blue LED has a simple structure, low cost, and high technology maturity, so it is used the most.