Quantum dots are nanoscale semiconductor particles that confine electrons (or holes) in all three spatial dimensions. Due to their tiny size—typically just a few nanometers across—the motion of charge carriers inside them is strongly restricted. This quantum confinement leads to the formation of discrete energy levels, much like the energy levels in atoms.
Because of this, quantum dots are often referred to as “artificial atoms.” Just as electrons in real atoms can only occupy certain energy levels, electrons in a quantum dot can only exist in specific quantized states. The spacing between these energy levels depends on the size and material of the quantum dot—smaller dots have wider energy gaps due to stronger confinement.
This behavior leads to several remarkable properties. For example, quantum dots can emit light of specific colors when excited, with the color tunable simply by changing the dot’s size. This makes them useful in applications like LEDs, lasers, biological imaging, and quantum computing. Their discrete, controllable energy states also make quantum dots ideal platforms for studying fundamental quantum effects and for building qubits in solid-state quantum devices.