Why does white ZnO (s) become yellow upon heating?

Hello Student
ZnO shown non stoichiometric defect under metal excess defect. When zinc oxide is heated it become yellow because on heating it loses oxygen because of which f-centers are generated which give yellow colour

When you heat ZnOZnO then Oxygen leaves as O2O2 leaving behind Zn2+Zn2 and 2 electrons. Zn2+Zn2 and the 2 electrons move to the interstitial sites of the crystal . This provides excess electrons in the crystal lattice of ZnOZnO. When light falls on these crystals then these electrons absorb a part of the light in the visible region and hence impart a yellow colour to the ZnOZnO.

ZnO when heated gives Zn2+ + 2electrons + 1/2 o2↑ these 2 electrons which are formed after heating move to the interstitial site of the crystal and when light falls on the crystal than these electrons absorb some part of the light and hence it shows yellow colour upon heating.

Dear Student,
Please find below the solution to your problem.

ZnO shown non stoichiometric defect under metal excess defect.
When zinc oxide is heated it become yellow because on heating it loses oxygen because of which f-centers are generated which give yellow colour

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