In the program, figures of the IR Detector card and the first energy source appear on the bottom left of the screen along with an energy scale labeled Input Spectrum. The Input Spectrum indicates the energy of light emitted by the visible source and absorbed by the computer-simulated IR detector card.
As you have for models of other types of luminescence, complete investigations by varying the energies of the source, the conduction band, and the valence band.
What relation must you have for the electrons to make a transition from the valence band to the conduction band?
If the light emitted by the first source provides enough energy for the electrons in the card to change energies from the ground state band to the excited state band, a transition (represented by a solid black arrow) is possible. Recall that you performed this experiment in the previous activity by placing colored transparencies over the IR detector card.
As with other computer models of solids, the gray and black illustrate that the electrons have changed energy.
Set up a situation in which transitions occur and electrons change energies. How much energy did the electrons in the detecting material lose as they made the transition from the excited state band to the impurity band? Explain how you determined this value.
The general scheme here is similar to that of phosphorescence. However, the change in energy when electrons move from the conduction band to the impurity and is much greater here. Similar to phosphorescence, the IR detector requires a second source of energy. In this case, of course, the second source is infrared light. We will now look at the energy band model for this process.