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What are F-centres?

What are F-centres?

Grade:12

3 Answers

chaman
36 Points
10 years ago
An F-Center or Farbe (German for colour) center is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more electrons, depending on the charge of the missing ion in the crystal or mainly due to the reason that when a compound is heated to a high temperature (mainly metallic oxides) the ions get excited and get displaced from their respective positions in their crystal structure but while doing so these ions leave behind some electrons in the vacated spaces. This leads to the phenomenon of colouring of compounds. This is used to identify many compounds, especially zinc oxide (yellow). Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored. Thus the origin of the name, F-center, which originates from the German Farbzentrum. The translation of this term also provides the synonym color center, which can also refer to such defects. F-centers are often paramagnetic and can then be studied by electron paramagnetic resonance techniques. The greater the number of F-centers, the more intense is the color of the compound. A way of producing F centers is to heat a crystal in the presence of an atmosphere of the metal that constitutes the material, e.g.: NaCl heated in a metallic Na atmosphere.
Keysang Yonthan
26 Points
6 years ago
F-centres are the sites from where anions are missing. Vaccant sites are occupied by electrons. F-centres contribute colour to the crystal.
Rishi Sharma
askIITians Faculty 646 Points
3 years ago
Dear Student,
Please find below the solution to your problem.

An F-Center or Farbe center is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more electrons, depending on the charge of the missing ion in the crystal or mainly due to the reason that when a compound is heated to a high temperature (mainly metallic oxides) the ions get excited and get displaced from their respective positions in their crystal structure but while doing so these ions leave behind some electrons in the vacated spaces.
This leads to the phenomenon of colouring of compounds.
This is used to identify many compounds, especially zinc oxide (yellow).
Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored.
Thus the origin of the name, F-center, which originates from the German Farbzentrum. The translation of this term also provides the synonym color center, which can also refer to such defects.
F-centers are often paramagnetic and can then be studied by electron paramagnetic resonance techniques.
The greater the number of F-centers, the more intense is the color of the compound.
A way of producing F centers is to heat a crystal in the presence of an atmosphere of the metal that constitutes the material,
e.g.: NaCl heated in a metallic Na atmosphere.

Thanks and Regards

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