What are nonstoichiometric point defects? explain with a diagram the formation of f-centers.
Question: What are nonstoichiometric point defects? explain with a diagram the formation of f-centers.
Nonstoichiometric point defects are a type of point defect in a crystal structure where the number of atoms of one element is not in the stoichiometric ratio. This can occur due to the presence of vacancies, interstitials or impurities in the crystal lattice.
F-centers are a type of nonstoichiometric point defect that are formed when an anion vacancy is created in the crystal lattice and an electron occupies the vacant site. The resulting negatively charged vacancy with an electron trapped in it is called an F-center. F-centers appear as color centers in crystals and are responsible for the colors of many gems.
The formation of F-centers can be explained with the help of a diagram. When a crystal lattice contains an anion vacancy, an electron from the valence band of the crystal can move into the vacant site, creating an F-center. This trapped electron has a lower energy than it would have in the valence band, which results in the absorption of light from the visible spectrum. The energy of the absorbed light corresponds to the energy difference between the valence band and the F-center energy level. This absorbed light gives the crystal its characteristic color.
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