LED uses phosphor to coat LED chips to achieve white light emission.
There are three main methods for LED to use phosphor to achieve white light emission, but none of them are fully mature, which seriously affects the application of white light LED in the field of lighting. Specifically, the first method is to coat the blue LED chip with yellow phosphor that can be excited by blue light, and the blue light emitted by the chip complements the yellow light emitted by the phosphor to form white light. This technology is monopolized by Japan’s Nichia Corporation, and a fundamental disadvantage of this solution is that the emission spectrum of Ce3+ ions in the phosphor does not have continuous spectrum characteristics, poor color rendering, and it is difficult to meet the requirements of low color temperature lighting. At the same time, the luminous efficiency is not high enough, and it needs to be improved by developing new high-efficiency phosphors.
The second implementation method is to coat green and red phosphors on the blue LED chip, and the blue light emitted by the chip is synthesized with the green and red light emitted by the phosphor to obtain white light with better color rendering. لكن, the effective conversion efficiency of the phosphor used in this method is low, especially the efficiency of the red phosphor needs to be greatly improved.
The third method is to coat the purple or ultraviolet LED chip with three primary colors or multi-color phosphors, and use the long-wave ultraviolet light (370nm-380nm) or purple light (380nm-410nm) emitted by the chip to excite the phosphors to achieve white light emission. This method has better color rendering, but it also has similar problems as the second method. At present, the red and green phosphors with higher conversion efficiency are mostly sulfide systems. This type of phosphor has poor luminescence stability and large light decay. Therefore, it has become a top priority to develop high-efficiency and low-light decay white light LED phosphors.
Using phosphors to make color LEDs has the following advantages:
First, although color LEDs of different colors such as red, yellow, أخضر, blue, and purple can be prepared without using phosphors, the luminous efficiency of these different color LEDs varies greatly. After using phosphors, the advantages of high luminous efficiency of LEDs in certain bands can be used to prepare LEDs in other bands to improve the luminous efficiency of the band. For example, some green band LEDs have low efficiency. Taiwanese manufacturers use the phosphors we provide to produce a high-efficiency LED called apple green for mobile phone backlights, which has achieved good economic benefits.
Secondly, the emission wavelength of LEDs is still difficult to control accurately, which will cause some wavelengths of LEDs to be wasted because they cannot be used. For example, when a 470nm LED is needed, an LED with a wider range of 455nm~480nm may be produced. The LEDs at both ends of the emission wavelength can only be processed or discarded at a relatively low price. The use of phosphors can convert these so-called waste products into the colors we need for our use.
Third, after using phosphors, the light color of some LEDs will become softer or brighter to meet different application requirements. Of course, phosphors are most widely used in the field of white light on LEDs, but due to their special advantages, they can also be used in color LEDs to a certain extent. لكن, the application of phosphors in color LEDs has just started and requires further in-depth research and development.