LED application prospects

Since 1962 the first red light emitting diode GaAsP light emitting diode, 40 years has been rapid development. In 1985, the luminous intensity of GaAlAs made the first breakthrough lcd. Since 90s, people have made a breakthrough in the development of LED. By using metal organic chemical vapor deposition (MOCVD) method instead of the complex liquid phase method, the high brightness yellow and yellow green light were produced by the research of InGaAIP four element material. Using the same MOCVD method with nitride as the representative of the blue and green LED made a historic breakthrough, the successful preparation of S.NaKamura high brightness InGaN blue and green LED, makes the LED formed three primary complete chemiluminescence system. In the past five years, the market of high brightness LED has expanded rapidly, and the market of high brightness LED has increased by an average of 53.7% per year from 1995 to 1999. With the rapid improvement of the efficiency of LED, the cost is declining, the LDE market is expanding from the display and indication to the lighting field, the experts predict that LED will become a new generation of light source after the incandescent lamp and fluorescent lamp.

Two methods for realizing white LED

White light is a multi color mixed light, can be felt by the human eye at least two kinds of light. For example, the human eye at the same time by the red, blue, green light stimulation, or at the same time by the blue light and yellow light stimulation can feel the white light. According to this principle, people can design the. In accordance with the existing technical capabilities, there are two possible solutions. First, use the RGB tricolor LED, according to the light intensity into matrix, three kinds of white light color mixing. However, LED is a PN junction, which, like all PN junctions, abide by the characteristics of the negative temperature characteristics of PN junction. The performance of the LED device is that the forward current decreases with the increase of the temperature, and the output of the light will decrease with the increase of the temperature, and the difference of the LED decreases greatly.

When the temperature rises to 120 degrees C, the green light output, only when the temperature of 20 degrees, while the blue LED can reach more than 90%, the result is mixed white light color difference.

The second is the use of blue light LED irradiation of a fluorescent material to produce complementary with the blue light Huang Guangping using the lens principle of complementary yellow light and blue light to be mixed, you can get the desired white light. In 1996, the Japanese company Nichia (NichiaChemical) found in the yellow light series of yttrium aluminum garnet (YAG) phosphor with blue light emitting diodes, white light source can be made. At present, people in the special violet and ultraviolet fluorescent powder development series, the emission wavelength of fluorescent powder is 370 ~ 420nm, by applying the method, this kind of fluorescent powder with violet or ultraviolet light can produce white light LED LED.

The principle and method of making LED light emitting

Basic principle

White LED is the use of LED based blue light, the blue part of the blue light emitted from the LED used to excite the fluorescent powder, the phosphors emit yellow green light or red light and green light, another part of the Blu ray transmission out, by the fluorescent powder of the yellow green light or red and green and blue white light transmission. The emission peak at 430nm or 470nm blue LED and yellow green phosphor composition can also be made of white light; blue and red emission peak of LED in 430nm or 470nm (650nm) and emission peak in 540nm LED white light green.

The method requires that the excitation wavelength of the phosphor is matched with the emitting wave length of the light emitting diode to ensure a high conversion efficiency, and the luminescence of the phosphor and the luminescence of the blue LED can be matched with the white light. Figure 4 shows that the peak value of the excitation spectrum of the phosphor is close to 470nm, which matches the emission wavelength of blue LED (470nm) very well.

Making method

White LED is on the surface of the blue GaN chip coated with yttrium aluminum garnet (YAG) phosphor.

The first LED chip placed on the wire structure with gold (Au) wire welding, then around the chip coated with YAG phosphor, and then sealed with epoxy resin, resin can play a protective role and to chip light gathering effect. The fluorescent powder layer to the surrounding light emitted from the LED chip in reflection, after many scattered absorption, finally to emit light, the spectral line of the LED peak is at 465nm, the half value width is 30nm, the blue spectrum is very sharp, YAG phosphor excited by blue light and yellow light (peak 555nm), eventually reach the external light is blue and yellow two colors, according to the complementary relationship, and additive color mixing to obtain visible white light.

Broad prospects for the application of white LED

LED with its compact and efficient, strong power, long service life, easy and computer, and other powerful advantages, including large screen display, traffic lights, car lights, LCD backlight and other aspects have been widely used, is currently in development to replace the traditional lighting lamps. The following will introduce several applications.

Solid-state lighting source

A high brightness red, blue and green LED made the lighting of various colors, not only can emit tunable wavelength, but also a brightness of up to hundreds of candelas of white light, as light source. Compared with the traditional light source, solid state light source has many advantages, such as low calorific value, low power consumption, long life, fast response, small size, flexible packaging, easy to develop thin and short products.

Currently, the white LED is still in the early stages of development. However, because of its unique advantages, the solid-state lighting source has been widely used in flashlight lighting, LCD backlighting (car audio, dashboard, mobile phone backlight board), traffic signals and indicators, room