Question

Define F- centre?

Answer 1

F - center:

• The F-centers are point defects and can be readily formed in alkaline halides.
• The anionic sites accumulated by unpaired electrons are called F-centres.
• Such defects impart color to the crystals.
• The color arises from the excitation of electrons when they absorb energy from visible light.
• F- center is a type of crystallographic defect.
• In this defect, the vacant site occurs through the missing anion is occupied by one or more electrons, based on the charge of the missing ion in the crystal.
• Electrons that are present in this vacancy tend to absorb light in a visible spectrum in such a way that the transparent material seems to be colored.
• An example of this crystal is $\mathrm{NaCl}$.