Here we need to mention a Nobel Prize winner, Dr. Shuji Nakamura. He invented the blue LED, which also laid a certain foundation for the white LED. He was awarded the Nobel Prize in Physics in 2014 for this significant contribution.

Shuji Nakamur

As for how blue LEDs are transformed into white LEDs, the biggest reason is that there is an extra layer of phosphor in the wafer.

In this picture, not only the N-type semiconductor layer, P-type semiconductor layer, and light-emitting layer mentioned above appear, but also a layer of "phosphor coating".

The basic light-emitting principle has not changed much: Between two layers of semiconductors, electrons and holes collide and recombine and produce blue photons in the light-emitting layer.