Metal Excess Defect in Zinc Oxide ZnO

The video tutorial explains the concept of metal excess defect, which occurs when excess cations and free electrons occupy interstitial positions in a crystal to maintain electrical neutrality. This defect imparts color to the crystal and enhances its electrical conductivity. The tutorial uses zinc oxide as an example, describing how it changes color from white to yellow upon heating due to the movement of zinc ions and free electrons. When light falls on these heated crystals, the free electrons absorb and emit yellow light, causing the yellow coloration.

What causes the metal excess defect in zinc oxide crystals?

How does the presence of free electrons affect the color of zinc oxide crystals?

Explain the process that occurs when zinc oxide is heated.

What happens to the free electrons when light falls on heated zinc oxide crystals?

Describe the relationship between the emission of yellow light and the heating of zinc oxide crystals.