When the current passes through the wafer, the electrons in the N-type semiconductor and the holes in the P-type semiconductor violently collide and recombine in the light-emitting layer to produce photons, which emit energy in the form of photons (that is, the light that everyone sees). Semiconductors of different materials will produce different colors of light, such as red light, green light, blue light and so on.
Between the two layers of semiconductors, electrons and holes collide and recombine and produce blue photons in the light-emitting layer. Part of the blue light generated will be directly emitted through the fluorescent coating; the remaining part will hit the fluorescent coating and interact with it to produce yellow photons. The blue photon and the yellow photon work together (mixed) to produce white light.