Quantum dots

A quantum dot is a nanoscale semiconductor crystal whose dimensions confine charge carriers, changing the allowed electronic states compared with those in a larger piece of the same material. As the crystal becomes smaller, confinement generally increases the energy spacing between states. The precise response also depends on composition, shape, surface chemistry and surrounding material, so size is important but not the only factor shaping a dot's properties.

When a quantum dot absorbs energy, an electron can be promoted to a higher-energy state, leaving a positively charged vacancy called a hole. Their bound pair is an exciton. As the excited system relaxes, it may emit a photon. In many semiconductor quantum-dot systems, smaller dots emit at shorter wavelengths and larger dots at longer wavelengths, although composition and structure also affect the spectrum. This tunability makes it possible to produce different colors from related materials by controlling their nanoscale dimensions.

Work leading to quantum dots developed across several laboratories and techniques. In the early 1980s, Aleksey Yekimov observed size-dependent quantum effects in copper-chloride nanocrystals embedded in glass; Louis Brus later demonstrated related effects in particles dispersed in a liquid. In 1993, Moungi Bawendi and colleagues developed methods for producing high-quality colloidal nanocrystals with more controlled properties. Yekimov, Brus and Bawendi shared the 2023 Nobel Prize in Chemistry for the discovery and development of quantum dots.

Quantum dots are used in some display technologies to help generate saturated colors and in some LED lighting to adjust emitted light. In research, their optical signals can label biological structures, and their semiconductor properties are investigated for solar-energy conversion and photonic devices. Use in biological or medical settings depends on the specific material, surface coating, delivery method and safety evidence; a promising imaging signal does not by itself establish a medical application as routine or risk-free. Incorporating individual dots into photonic circuits also requires precise placement and measurement, which remains an engineering challenge.