Abstract

When the radius of a nanoparticle is reduced below its Bohr exciton radius, the nanoparticle electronic energy structure becomes confined, leading to a set of unique properties which enable a range of new applications. Quantum confinement is generally observed in the widening of the band gap, where the band gap energy becomes inversely proportional to particle size. The possibility to tune the energy gap by controlling particle size is an intriguing and exciting aspect of quantum-confined materials, which allows us to fine-tune material properties as per application requirements. In addition to an increase in the band gap energy, other changes following quantum confinement of the energy structure are as follows: a change in the oscillator strength; an enhancement of carrier life times, necessary for carrier multiplication or hot-carrier extraction; and a change in transition dynamics, for example, a shift toward direct band gap behavior for silicon.