Appendix

Primer on fluorescence:
Fluorescent materials emit light when light is shined upon them. Open up the fluorescence program in Spectroscopy Lab Suite. Choose create "excited state band."

Primer on Fluorescence

This is the excited energy state valence state atoms transition into when a certain amount of energy has been received. Now, click on "create impurity state band." This band serves as a midway transition point for atoms returning from excited state back to ground state. No light is emitted during transition from conduction band to impurity band; heat is generated during this stage. Light is only emitted during the transition from the impurity band to the valence band. Now adjust the input spectrum on the bottom left hand size of the screen; as you drag the slider, a golden pointer will appear on the right side of your screen next to the transition diagram. Observe how much energy is needed to turn on the lamp by clicking on button "Turn on lamp."

How much energy is required to turn on the mercury lamp?

How does this amount relate to the valence band energy and the conduction band energy?

The input energy needs to be greater than the energy gap difference between the conduction band and the valence band for the mercury lamp to turn on.

Turn on the lamp. The mercury gas should change its color depending on the input spectrum, but does the phosphor coating depend on the input spectrum as well?

Try changing the input spectrum and see if there are any differences in the output spectrum or the color of emitted light.

We now see that the color of the light does not depend on the input spectrum, at least not directly. Now, try modifying the placement of the conduction band. Does that change the output spectrum?

Changing the placement of the conduction band may require a higher input energy, but the change does not affect the output spectrum. Now, let us modify the placement of the impurities band. Any changes?

Voila, the color emission changes! Now, how does the output spectrum correlate to the different energy levels? Now we know that the output spectrum has something to do with the impurities band, let's make some simple calculations to see which transition produces light. Note: the following may be ranges of numbers.

Energy level of conduction band eV
Energy level of impurities band  eV
Energy level of valence band      eV

Output spectrum energy               eV

Energy level of conduction band - energy level of impurities band eV
Energy level of impurities band - energy level of valence band      eV

The transition from impurities band to valence band is the transition that produces the output spectrum. The energy from the transition from conduction band to impurities band produces heat instead of light.