Energy Levels in Fluorescence

 

The first step in any light emitting process is to give electrons in the lowest energy states enough energy to change to a higher energy level (Figure 3). In a solid with an impurity band the electrons in the conduction band do not necessarily lose all their energy at once and return directly to the ground state. Instead, these electrons lose enough energy to nearby atoms that they move from the conduction band into the impurity band. This transition is represented by a dashed arrow which is illustrated in the animation.

 

The output spectrum which we see is the result of electrons losing energy as they move from the impurity state band to the ground state band.

 

Ordinary fluorescent tubes operate when an electric current passes through a tube filled with mercury gas. The excited mercury atoms emit visible and UV light. The UV light which has an energy of about 3-5 eV is converted to visible light by the process described here.