Luminescence

Luminescence is the optical radiation of a physical system that arises in the transition from an excited state to the ground state ( radiative deactivation ). Depending on the type of excitation distinguishes different types of luminescence:

Always occurs in addition to the luminescence and heat radiation emitted by each of the body temperature.

The different types of luminescence can also be classified according to the duration of the glow after the end of excitation. A very short persistence ( usually < a millionth of a second ) as a direct result and side effect of excitation is referred to the concept of fluorescence, whereas phosphorescence describes a longer persistence of at least 1 /1000 second after excitation.

The explanation for operations both belts provides the model: By the excitation of the substance, the electrons pass from the valence band into the conduction band. In the case of fluorescence these conduction electrons recombine with the emission of electromagnetic radiation again directly with an electron vacancy in the valence band. The light intensity is directly dependent on the actual excitation energy.

In phosphorescence, however, metastable intermediate levels in the forbidden zone, by means inserted into the material impurities, produced the so-called stick or Aktivatorterme. In the ground state the Aktivatorterme are occupied with electrons, the traps remain empty. Once the electrons have been lifted into the conduction band by the excitation from the valence band, the resulting holes are filled with electrons from the Aktivatortermen. The free electrons are eager to recombine with the holes from the Aktivatorterm. They are captured by the traps. It is also possible that the electrons are given directly into the trap site from the valence band ( direct excitation ). By re- action of energy, these electrons can be raised back into the conduction band, and from there to recombine under emission of light energy with holes from the Aktivatorterm.

Studying the luminescence, for example, in crystals is performed by means of the Phosphoroskops Becquerel.