Single Choice

Select the correct statement regarding F-centre.

AElectrons are held in the voids of crystals.
BF-centre imparts colour to the crystal.
CConductivity of the crystal increases due to F-centre.
DAll the above.
Correct Answer

Solution

When Potassium chloride is heated in sodium vapour, we see that is acquires a yellow colour. The heating in excess sodium creates new lattice sites for sodium. To maintain the structure, an equal number of chloride sites are also created but the latter are vacant. The electron of the potassium atom that is ionized in the KCl matrix is trapped by the chloride ion vacancy. This trapped electron can be freed into the crystal by absorbing visible light and hence, the colour. A trapped electron at an anion vacancy is an electronic defect and it is known as F-centre.

SIMILAR QUESTIONS

Solid State

ZnO is white when cold and yellow when hot because it____.

Solid State

The appearance of colour in solid alkali metal halides is generally due to:

Solid State

Which of the following statements is/are correct ?

Solid State

Select the correct statement(s) regarding defects in solids:

Solid State

$$ZnO$$ is white when cold and yellow when heated. It is due to development of:

Solid State

Analysis shows that nickel oxide has the formula $$Ni_{0.98}O_{1.00}$$. What fractions of nickel exist as $$Ni^{2+}$$ and $$Ni^{3+}$$ ions?

Solid State

Zinc oxide loses oxygen on heating according to the reaction. $$ZnO\xrightarrow { heat } Zn^ { 2+} +\frac { 1 }{ 2 } O_ 2+2e^-$$ It becomes yellow on heating because:

Contact Details