Chemistry - Complete d-block Question with Solution | TestHub

Heating ZnO causes it to lose oxygen, creating non-stoichiometric defects known as F-centers. These are anionic vacancies occupied by unpaired electrons. These electrons absorb light in the visible region, leading to the yellow color. The reaction is:

$ZnO\stackrel{\Delta }{\to }Z{n}^{2+}+\frac{1}{2}{O}_2+2e^{-}$

The released electrons get trapped in the oxygen vacancy creating F-centers.