Energy Bands and Fluorescence 

 

The energy diagram on the right of the computer screen represents the material in the phosphor. The black set of horizontal lines at -5 eV represent the valence band of the phosphor coating. Click on the Create Excited State Band (conduction band) button, then on the Create Impurity State Band button. A set of gray horizontal lines representing these bands appear. You may drag the energy bands to other values.

 

An energy scale labeled Input Spectrum will now appear below the cross section of the fluorescent tube. The input spectrum corresponds to the energy of light emitted by the mercury gas and striking the phosphor coating. Visible light in this spectrum passes through the glass tube and is characteristic of the mercury gas spectrum. UV light is absorbed by valence electrons of the phosphor.

 

Vary the energy of the input spectrum and the energies of the conduction and impurity bands so that you can determine the conditions necessary for the lamp to turn on. Record your observations.