Quantum confinement refers to the phenomenon where the electronic and optical properties of materials change dramatically when their size is reduced to the nanometer scale — typically below 10 nanometers. At this scale, the motion of electrons and holes is restricted to such small dimensions that quantum mechanical effects dominate.
In bulk materials, energy levels are continuous because particles can move freely in all directions. However, in nanostructures like quantum dots, nanowires, or quantum wells, particles are confined in one or more dimensions. This spatial restriction means electrons and holes can only occupy discrete, quantized energy levels — similar to electrons in atoms. As a result:
- Energy levels become discrete instead of continuous.
- Band gaps widen as the structure gets smaller.
- The optical and electronic properties (such as absorption and emission wavelengths) shift with size.
This is why quantum dots of different sizes emit different colors of light — smaller dots emit bluer (higher energy) light, while larger dots emit redder (lower energy) light.
Quantum confinement is critical in modern technologies like semiconductor lasers, photodetectors, solar cells, and biological imaging, where tuning properties at the nanoscale allows for precise control of device behavior.