In order to apply LEDs to lighting devices, three-color LEDs of red, green, and blue can be used to form white light. Although this can solve the problem of not being able to produce white light in the past, this device also has many disadvantages. Not only is the cost too high, but the three LEDs have different lifespans. If one of them is damaged, the device must be eliminated. Therefore, scientists from all over the world are also actively looking for solutions, and the answer to this problem is - phosphors.

The inorganic powder as the basic material of light-emitting diode is called phosphor powder. This material has high light energy conversion efficiency and high color saturation, and the synthesis and processing steps are simple. It can be mainly divided into two parts: host lattice and activator. The host lattice is the main crystal structure of the phosphor and provides the coordination environment of the activator, which will affect the emission characteristics of the activator.

The activator is an ion doped in the host, which is the main luminescent center, usually a rare earth element. The most famous phosphor is cerium-doped yttrium aluminum garnet (YAG), which was revealed by Nichia in 1996. This phosphor can be excited by blue LEDs (wavelength is 460 nanometers). The yellow light emitted by YAG can be obtained by appropriately adjusting the amount of phosphor added, and the blue light emitted by the blue LED chip can be obtained, plus the yellow light emitted by the YAG yellow phosphor, white light can be formed. This device is not only low cost, but also avoids the problem of different lifespans faced by using three different color LEDs.