there are many ways for led to realize white light, and the way that was developed earlier and industrialized is to coat phosphor on led chip to realize white light emission.
there are three main methods to realize white light by using phosphor in LED, but they are not fully mature, which seriously affects the application of white led in lighting field. Specifically, the first method is to coat the blue LED chip with yellow phosphor which can be excited by blue light, and the blue light emitted by the chip and the yellow light emitted by the phosphor complement each other to form white light. This technology is monopolized by Japan's Nichia company, and a principle disadvantage of this scheme is that the emission spectrum of Ce3+ ions in the phosphor does not have continuous spectral characteristics, and the color rendering is poor, which makes it difficult to meet the requirements of low color temperature lighting, and the luminous efficiency is not high enough, so it needs to be improved by developing new efficient phosphors.
the second method is to coat the blue LED chip with green and red phosphors, and get white light by combining the blue light emitted by the chip with the green and red light emitted by the phosphors, which has good color rendering. However, the effective conversion efficiency of phosphor used in this method is low, especially the efficiency of red phosphor needs to be greatly improved.
the third method is to coat three primary colors or multi-color phosphors on the purple light or ultraviolet light LED chip, and use the long-wave ultraviolet light (37nm-38nm) or purple light (38nm-41nm) emitted by the chip to excite the phosphors to realize white light emission. This method has better color rendering, but it also has similar problems as the second method. At present, most of the red and green phosphors with high conversion efficiency are sulfide systems.
we are the first research institution in China to study high-efficiency and low-light-decay phosphors for LEDs. Recently, through the joint research with our partners in Taiwan Province, a variety of color LEDs with phosphors have been developed.
Using phosphor to make color LEDs has the following advantages:
First, although different colors of LEDs such as red, yellow, green, blue and purple can be prepared without using phosphor, the luminous efficiency of these LEDs with different colors is quite different. After using phosphor, LEDs with some bands can be prepared with the advantages of high luminous efficiency, so as to improve the luminous efficiency of other bands. For example, some green-band LEDs have low efficiency. Taiwan Province manufacturers use the phosphors provided by us to prepare a kind of LED with high efficiency, which is called "Apple Green" for the backlight of mobile phones, and achieved good economic benefits.
Secondly, it is still difficult to accurately control the light-emitting wavelength of LED, which will lead to the waste of some wavelengths. For example, when it is necessary to prepare 47nm LEDs, it is possible to prepare LEDs with a wide range from 455nm to 48nm. The LEDs with light-emitting wavelengths at both ends can only be disposed of or discarded at a low price, and these so-called "wastes" can be converted into the colors we need to use by using phosphor.
thirdly, after using phosphor, the light color of some LEDs will become softer or brighter to meet the needs of different applications. Of course, the most extensive application of phosphor in LED is in the field of white light, but it can also be used in color LED due to its special advantages. However, the application of phosphor in color LED has just started, and further research and development are needed.