Thermoluminescence trapping

[ctydtgat]

When thermo-luminescent materials are illuminated with UV or deep blue, luminescent centers can be excited or even ionized so that the electron gets trapped into a level just below the conduction band, typically 0.4 to 1 eV.
Why is it that the trapped electrons are not released from the trap again by the excitation source? I would expect that there are enough levels to go to high in the conduction band or at least there may be trap energies where this could happen.
Thanks!

 

[BigJDubs]

The answer to your question is that the trap depths in thermoluminescent materials are usually too deep for the excitation source to be able to release the trapped electrons. The trap depths are typically 0.4 to 1 eV, while the energy of the excitation source (UV or deep blue) is usually much lower than this. As a result, the excitation source is not able to provide enough energy to release the electrons from the traps.