Quantum Dots Flashcards
Define an exciton.
When an e- jumps to the conduction band, leaves a vacancy in the valence band. The e- becomes attracted to the hole.
What is the difference between a strongly bound and weakly bound exciton?
Strong: size of crystal lattice
Weak: over several unit cells
What effect does excitons have on the energy levels?
The quantised energy levels are reduced, proportionally to the Rydberg energy.
Describe the effective potential in a semiconductor.
The semiconductor cubic particle has a size-dependent effective band gap. (blue shift caused by confinement)
Describe the difference between weak and strong confinement.
weak: radius of nanoparticle is a few exciton radii
strong: nanoparticle radius is smaller than exciton radius
How does energy change in confinement?
it is quantised by confinement and reduced by the exciton energy.
What are advantages of QDs as Fluorophores?
- insulating shell, protected from oxidation, longer lifetime
- broad absorption spectra, can excite different QDs with same source
- narrow emission spectra so can resolve the signal from different QDs
