on heating crystals of kcl in pottasium vapours the crystal starts exhibiting a voilet colour.Why?
Answers
Answered by
4
It is a similar phenomenon only here we are doping KCl with xs K to give K(1+x)Cl. The lattice is missing some Cl- ions and to keep the lattice electrically neutral free electrons occupy the holes (vacant sites).
I believe however that the color is due to a different mechanism since it is violet that is observed which means low energy red is being absorbed (the band gap in KCl is much greater than in ZnO).
I have seen this color in naturally occurring fluorite (the have "color centers": missing F^- ions). The violet looks similar to the blue/violet solutions of Na (K) in liquid ammonia. There is one theory that the free e-s in these NH3 solns occupy large cavities produced by the NH3 molecules (N-Hδ+....e-) and the transition is from a giant s-type MO to a p-type MO. I think the same could be happening in the anion deficient solids.
I believe however that the color is due to a different mechanism since it is violet that is observed which means low energy red is being absorbed (the band gap in KCl is much greater than in ZnO).
I have seen this color in naturally occurring fluorite (the have "color centers": missing F^- ions). The violet looks similar to the blue/violet solutions of Na (K) in liquid ammonia. There is one theory that the free e-s in these NH3 solns occupy large cavities produced by the NH3 molecules (N-Hδ+....e-) and the transition is from a giant s-type MO to a p-type MO. I think the same could be happening in the anion deficient solids.
Similar questions