What are excitons?

Coulomb interaction between electrons and holes can give rise to new excitations in

matter- these are called excitons.

Generally electrons and holes are created in the conduction and valence band of a solid

due to optical absorptions. Therefore, when we talk about excitons -there is always a

corresponding inter-band transition associated with it.

Excitons are seen mainly in semiconductors and insulators. Metals generally donot show excitonic effects due to large screening. But

there are exceptions.“hydrogenic system”