The source of electromagnetic radiation is atoms, when the atoms of an element are in an excited state
The source of electromagnetic radiation is atoms, when the atoms of an element are in an excited state, they return to a lower energy state by emitting electromagnetic (EM) radiation. The transition of the electronics in the atom from higher energy level to a lower unique energy level for the occupation of electrons, due to this EM spectrum emitted is a unique signature of an element or a substance. The study of the characteristics of EM radiation emitted by atoms is called Atomic Emission Spectroscopy.