What is f centre give some example also
What is f centre give some example also
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 ionin the crystal. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored..
e.g.:NaCl heated in a metallic Na atmosphere.
Na0 → Na+ + e−
Na+ is incorporated at NaCl crystal.
Cl− vacancies are generated, because of the excess of Na+...
The electrons present in f centre absorbs the visible light to get excited it which makes the alkali metal coloured.
When Potassium chloride is heated in sodium vapour, we see that is acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created, but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F centre.
Hope this helps :)
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 ionin the crystal. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored..
e.g.:NaCl heated in a metallic Na atmosphere.
Na0 → Na+ + e−
Na+ is incorporated at NaCl crystal.
Cl− vacancies are generated, because of the excess of Na+...
The electrons present in f centre absorbs the visible light to get excited it which makes the alkali metal coloured.
When Potassium chloride is heated in sodium vapour, we see that is acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created, but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F centre.
Hope this helps :)
