Quantum dots (QDs) are nanosized particles with electronic and optical properties that differ from the bulk material. They can be used, for example, to improve light-emitting diodes (LEDs) or in medical imaging. However, in these applications, they can be submitted to high temperatures or oxidizing conditions, which can cause a decline in their photoluminescence quantum yield.

Elijah Thimsen and colleagues, Washington University in Saint Louis, MO, USA, have coated CdTe quantum dots with Al₂O₃ shells to protect the QDs from degradation under harsh conditions. The team used atomic layer deposition (ALD) to deposit the alumina onto the quantum dots by exposing them first to gaseous trimethylaluminum, then to water vapor, and repeating the process several times. The CdTe quantum dots have diameters of 3.6 nm, the final alumina shells have a thickness of about 20 nm.

The researchers tested the effect of the Al₂O3 shells on the quantum dots’ stability by exposing them to 90 °C heat in air for 17 hours under continuous illumination. The coated QDs retained 94 % of the initial photoluminescence quantum yield after this treatment, while uncoated control samples only retained 33 % due to extensive oxidation.

• Quantum dots protected from oxidative attack using alumina shells synthesized by atomic layer deposition,
  B. Yin, B. Sadtler, M. Y. Berezin, E. Thimsen,
  Chem. Commun. 2016.
  DOI: 10.1039/c6cc05090e