LED coated with phosphor powder on the LED chip to achieve white light emission.
There are three main methods to realize white light with phosphor powder, but they are not completely matured. So the application of LED in the field of illumination is seriously affected by LED. Specifically, the first method is applied to the blue LED chip which can be excited by the yellow phosphor blue light, the chip issued by the blue light and fluorescent powder is issued by the Yellow light. The technology is monopoly by Japan Nichia, and the principle disadvantages of this scheme is the emission spectra of Ce3 + ions in the phosphor not continuous spectrum, color index is poor, it is difficult to meet the requirements of low color temperature lighting, and luminous efficiency is not high enough, through the development of new and high efficiency fluorescent powder to improve.
The second realization method is the blue LED chip is coated with green and red phosphor, the blue light emitted by the chip, the green and red light emitted by the fluorescent powder are obtained, and the color index is better. However, the efficiency of this method is not very high, and the efficiency of the red phosphor is greatly to be improved.
The third method is in the violet or ultraviolet LED chip coated tricolor or multiple color fluorescent powder, using the chip emit UVA light 370nm-380nm or violet (380 nm -410nm) to stimulate phosphor and realize white light emission, the method has better color index, but also exists the same problem with the second method, and the transformation efficiency of red and green fluorescence powder for curing objects, this kind of phosphor with poor stability, attenuation is larger. So the development of efficient, low depreciation of white LED fluorescent powder has become an urgent mission.
LED domestic research institution with high efficiency and low light decay phosphor research was firstly lunched in China. Recently, through cooperated research with China’s Taiwan partners, a variety of color LED using fluorescent powder was developed.
Taking fluorescent powder to produce color LED has the following advantages:
Firstly, although without the usage of fluorescent powder, we can make different colors LED, such as red, yellow, green, blue, purple, and so on. Due to the different color LED luminous efficiency of the difference is very large, the fluorescent powder, and with the advantages of some band led luminous efficiency of other bands led, in order to improve the luminous efficiency of the band. For example some green band led efficiency is not high, Taiwan manufacturer use our fluorescent powder to prepare a kind of high efficiency, regarded as “apple green” led for mobile phone backlight, which has good economic benefit.
Secondly, LED light-emitting wavelength it is hard to control accurately, which will cause some led wavelength without application and wasted, such as the production of 470 nm LED may prepared from 455 nm to 480 nm in a wide range of LED, the emission wavelength at both ends of the LED only to lower the price of disposed of or abandoned,. But, taking the fluorescent powder can transfer the so-called “waste” into the color we need and get application.
Thirdly, after the use of fluorescent powder, some LED color will become softer or bright to meet different needs. Of course, fluorescent powder applied in the LED is widely used in the field of white light, but because of its special advantages, in the colorful LED can also get used, but the application of fluorescent powder in the colorful LED is still on the beginning and need to deeply research and development.