Why LiCl acquires pink colour when heated in Li vapours?

The Cl- ions diffuse to the surface and form LiCl with ${{Li}^{+}}$ ions. An electron is released which diffuses into the crystal and occupies the anionic site. Such anionic sites occupied with electrons are called F-centres. These impart pink colour to the crystal. The colour results by the excitation of the electrons on absorbsing energy from visible light falling on the crystals