Shrinking a semiconductor nanocrystal below its exciton Bohr radius confines electrons and holes in a finite "box," raising their kinetic energy (particle-in-a-sphere quantum confinement). This widens the effective bandgap, blue-shifting the emitted photon as the dot gets smaller.
E_g(R) = E_g,bulk + (hbar^2 * pi^2) / (2*mu*R^2) (Brus equation, simplified)
lambda_emit = 1240 / E_g(R) [nm, with E_g in eV]
- Dot radius - the physical nanocrystal size; smaller radius means stronger confinement and a bigger energy shift, visibly moving the glowing dot's colour toward blue/violet.
- Material - CdSe, InP and PbS have different bulk bandgaps and effective masses, giving each a different base colour and size sensitivity.
- Excitation intensity - how strongly the dot is "pumped," scaling the brightness and electron-cloud animation speed (not the colour, which is confinement-only).
- Toggle electron cloud - shows/hides an animated probability-density point cloud representing the confined electron wavefunction inside the dot.
Real-world application: this size-tunable emission is exactly why quantum dots are used in QLED TV displays, biomedical fluorescent tags and next-generation solar cells - one material, many colours, just by controlling nanocrystal size during synthesis.