With example explain F-center.

Asked by Topperlearning User | 17th Jun, 2016, 10:43: AM

Expert Answer:

F-centers is the anionic site occupied by the electron ( e– becomes part of the lattice). These electrons are color centers, often referred to as F-centers (from the German word farben meaning color).

For example, when NaCl is heated in an atmosphere of Na vapour, the excess of Na atoms deposit on the surface of NaCl crystal. Cl− ions then diffuse to the surface where they combine with the Na atoms which becomes ionized by losing electrons. These electrons diffuse back into the crystal and occupy the vacant sites created by the Cl ions. These electrons absorb some energy of the white light. giving yellow colour to NaCl. Similarly, excess of Li in LiCl makes it pink and excess of K in KCl makes it violet.

Answered by  | 17th Jun, 2016, 12:43: PM