The appearance of colour in solid alkali metal halides is generally due to :
Schottky defect
Frenkel defect
Interstitial position
F-centres
As we have learned
No. of atoms(z) for face centered unit cell -
Lattice points: at corners and face centers of unit cell.
For face centered cubic (FCC), z=4.
- wherein
One to excitation of free electrons in f- centre , When light in visible spectrum is incident on the crystal , coloration is observed
Option 1)
Schottky defect
Option 2)
Frenkel defect
Option 3)
Interstitial position
Option 4)
F-centres
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