2023 Nobel Prize in Chemistry
Reason for Award
for the discovery and synthesis of quantum dots
Laureates
Tunisia, 
France, 
United States of America
United States of America
Russian Federation
Explanation
There are tiny specks so small that their colour changes with size. Mr. Bawendi, Mr. Brus and Mr. Ekimov found these specks, called quantum dots, and learned how to make them well. By simply changing their size, the dots can glow red, green or blue and are already used in TVs and LED lamps. Doctors are testing them to light up cancer inside the body. It is like discovering magic in the very small world.
Related Keywords
quantum dot
A quantum dot is a semiconductor nanocrystal in which carriers are confined in all three dimensions. When its diameter approaches the electron de-Broglie wavelength, energy levels become discrete and the band gap shifts visibly. Merely tuning the size over a few nanometres allows precise control of emission colour while maintaining high stability and quantum yield. Colloidal synthesis and epitaxial growth enable scalable production of monodisperse dots. They are now used in displays, LEDs, photovoltaics, bio-imaging and quantum optics.
band gap
The band gap is the energy difference between the valence and conduction bands in a semiconductor. In quantum dots, confinement effectively widens the band gap in a size-dependent manner. As the dot shrinks, absorption and emission shift to higher energies (bluer light), providing direct evidence of quantum confinement. Band-gap engineering is essential for wavelength-tuned emitters and optimized solar absorbers. The effective-mass approximation and k·p methods quantify the relationship, guiding material design.
nanocrystal synthesis
Nanocrystal synthesis is the chemical process of precisely controlling nucleation and growth to obtain uniform particle sizes. In Bawendi’s hot-injection method, precursors are rapidly injected into a hot solvent, creating a burst of nucleation under supersaturation. Subsequent cooling slows growth and narrows the size distribution. Surface ligands passivate dangling bonds and tune solubility and growth kinetics. Continuous-flow reactors and automation now scale the process for industry.
cadmium selenide
CdSe is the most extensively used II–VI semiconductor in quantum-dot research. Its bulk band gap is 1.74 eV, but shrinks to over 2 eV (green emission) at a 3 nm diameter due to confinement. Coating a CdSe core with a ZnS shell dramatically improves photostability and quantum yield. Although cadmium-based dots offer high colour purity and facile synthesis, toxicity concerns drive substitution by InP and other materials. CdSe remains important in optoelectronics and bio-probes.
surface ligand
Ligands bind to dangling surface atoms of quantum dots, preventing oxidation and aggregation. Trioctylphosphine oxide and long-chain carboxylic acids are typical examples and also influence electronic structure. Ligand exchange can render dots water-soluble or improve conductivity, giving flexibility for device integration. Excess insulating ligands impede charge transport, so optimisation is crucial. The topic merges interfacial science with organic chemistry.
colloidal solution
Quantum dots are often synthesised and stored as colloids dispersed in organic solvents. In colloidal form they can be deposited by solution processing or ink-jet printing, fitting large-area device fabrication. Electrostatic and steric stabilisation prevent precipitation and ensure shelf life. Dispersibility depends strongly on ligand chemistry and solvent polarity. Surface modification enables transfer to aqueous or polar media as needed.
photoluminescence quantum yield
Photoluminescence quantum yield (QY) is the ratio of emitted to absorbed photons and is a key performance metric. In quantum dots, surface defects act as non-radiative centres that lower QY. Bawendi’s core–shell engineering achieved QYs over 90 % in CdSe/ZnS dots. High QY determines colour purity in displays and detection sensitivity in bio-imaging. Measurements employ integrating spheres or reference fluorophores.
energy transfer
Quantum dots can serve as donors or acceptors in Förster resonance energy transfer (FRET). Their size-tunable spectra allow broad wavelength engineering, enabling biomolecular distance measurements. Carrier multiplication through multiple-exciton generation may enhance solar-cell efficiency. Proximity to metal nanoparticles induces plasmon-enhanced energy transfer, boosting emission. Both fundamental physics and technological applications drive extensive research.
QLED display
QLED displays employ quantum dots either as colour converters atop an LCD backlight or as electroluminescent layers. Blue LED or OLED light is converted to red and green by quantum dots, yielding a wide colour gamut and high brightness. Precise size control allows coverage of the Rec.2020 standard. Ink-jet printing enables patterned deposition, expanding applications from large TVs to mobile devices.
bioimaging
Quantum dots outshine organic dyes and resist photobleaching, making them ideal for bioimaging. Conjugating peptides or antibodies enables targeting of specific cells or proteins. Near-infrared emitting dots penetrate tissue, allowing deep-tissue observation. Clinical trials explore intraoperative tumour guidance and drug-delivery tracking. Assessing in-vivo clearance and heavy-metal toxicity remains a critical challenge.