Question

10. What are F-centres? What is the effect of F-centres?

Answer 1

The negative sites occupied by unpaired electrons are called F-centres. Such defects also impart color to the crystals. The color results by excitation of these electrons when they absorb energy from the visible light falling on the crystals.

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Answer 2

Answer:

When the anionic sites of a crystal are occupied by unpaired electrons, the ionic sites are called F-centres. These unpaired electrons impart colour to the crystals. For example, when crystals of NaClare heated in an atmosphere of sodium vapour, the sodium atoms are deposited on the surface of the crystal.