Quantum confined electrons: What are these?
Answer: Normally electrons in bulk metals are able to move from end to end under the influence of a voltage potential. Electrons within atomic clusters are bound to be limited in their movement by the confines of small spaces and this causes a kinetic energy much like a compressed spring. When during a collision with a photon of the right wavelength that additional energy is dissipated and added to the receeding photon to gain some energy instead of loosing it.