May 27, 2026 -- The nanocrystals that won the 2023 Nobel Prize in Chemistry have revealed an unexpected property. Researchers at the University of Twente discovered that the molecular coating on quantum dot nanocrystals generates internal electric fields. Depending on which coating is used, these fields slow light output by a factor of eight. The findings, published in the Journal of Physical Chemistry C, have potential applications in silicon photonics and single-molecule electric-field sensing.

Quantum dots are already everywhere. They give QLED televisions their vivid colours and help solar cells convert sunlight more efficiently. In all these applications, controlling how much light a quantum dot emits is important. Quantum dots are semiconductor nanocrystals just a few nanometres in diameter. They are small enough that quantum mechanical effects determine their behaviour. The colour of light they emit depends on their size: smaller dots emit blue light, larger dots emit red. This size-tuneable emission is what earned Moungi Bawendi, Louis Brus, and Alexei Ekimov the 2023 Nobel Prize in Chemistry. Until now, that control was thought to come primarily from the size of the nanocrystal. This study shows that the surface coating is an equally powerful dial. It changes how quantum dots could be applied.

Integrating light emitters into silicon chips

The quantum dots in this study emit in the near-infrared range, invisible to the human eye but critical for telecommunications and silicon-based optical systems. Their surfaces are coated with molecules called ligands, which prevent the nanocrystals from clumping together in solution. What this study reveals is that ligands do more than stabilise. Certain ligands generate electric fields inside the nanocrystal that interfere with the light-emitting process. This is known as the quantum-confined Stark effect, a phenomenon previously observed in visible-range quantum dots but not in the near-infrared range. The findings are particularly relevant for silicon photonics. Integrating light emitters into silicon chips has long been a bottleneck. Quantum dots are a promising candidate, and understanding how to tune their emission through surface chemistry brings that integration a step closer.

The coating changes everything

The team examined quantum dots with varying sizes and two different surface coatings: oleic acid and polyethylene glycol (PEG). Dots coated with oleic acid behaved as expected, their emission rates scaled predictably with particle size. Dots coated with PEG told a different story. At smaller sizes, PEG-coated dots emitted photons up to eight times more slowly. The PEG molecules create a tiny electric field inside the nanocrystal. That field disrupts the light-emitting process.

First author Andreas Schulz: “We found that the special coating on the quantum dots creates tiny electric fields. These fields change the results of our measurements, showing how important the surface chemistry is when studying semiconductor nanocrystals.” Silicon chips also play a role. When quantum dots are placed on a silicon surface, their emission rates increase by up to a factor of ten, simply because of the material they are sitting on.

Willem Vos is enthusiastic: “Our results reveal exciting new ways to dynamically control light at the nanoscale. This paves the way for the photonic community to develop next-generation ultrafast optical modulators, highly sensitive electric-field sensors, and advanced bio-photonic devices with unprecedented performance and tunability.”

About the researchers

The research was conducted by Andreas Schulz, Christian Blum, Jurriaan Huskens, Julius Vancso, and Willem Vos at the University of Twente. The study was funded by the Dutch Research Council (NWO). The paper “Emission of Photons by Near-infrared PbS Quantum Dot Nanocrystals for a Large Diameter Range” is published in the Journal of Physical Chemistry C.