The Energy Band Model

This band is usually empty, it contains few or no electrons since energy is required for them to get there from the valence band. Electrons in the conduction band are free to move about the crystal, thus the name conduction band.

If an electron does manage to get to the conduction band, it resides there for mere fractions of a second (an average lifetime). When it loses its energy it drops back down to the valence band emitting its energy as heat, light or by transferring it to another electron.