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What are Quantum Dots?

By , BPharm

A quantum dot is a semiconductor nanocrystal with unique properties distinct from bulk semiconductors or discrete molecules. The excitons are confined in all three spatial dimensions, lending to their optical and electrical properties that prove useful in biomedical imaging, as well as the possibility for use in electronic devices and solar energy systems.

Properties

Quantum dots are not all uniform and, as a result, the properties of a quantum dot can vary greatly depending on its individual size and shape.

Crystals smaller in size generally have a larger band gap, which means there is a greater difference between possible energy levels of the crystal. In this case, more energy is needed to excite the quantum dot and more is released when it returns to resting state. This affects the way the dots emit signals and may offer utility in medical or electrical fields today. When using fluorescent dye, for example, using smaller crystals would result in a shift in color from lower-energy red to higher-energy blue light.

Use in Medical Imaging

Quantum dots offer a novel method of medical imaging that can provide accurate and precise results. As the production of the crystals can be highly controlled to manage the size and shape of the crystals the conductive properties can easily be predicted to help with interpretation of the results.

The ability to regulate the size and, therefore, potential energy of the crystals allows them to be used for specific purposes. Smaller crystals that are associated with larger energy changes, for example, display more subtle quantum effects that may offer utility in some imaging types.

Use in Photovoltaic Cells

Traditional solar cells use silicon based cells to convert light energy emitted from the sun into electrical energy that can be used. Quantum dot voltaic cells benefit from the innate ability of quantum dots to absorb light of the frequency from the sun and become excited. This energy can then be harnessed and used as an electric current.

At present, quantum dot photovoltaic cells exist but are less efficient than the traditional silicon model. The can effectively convert approximately 9% of the energy from sunlight into electrical energy, which will hopefully be improved with further research and development.

Use in Computing

Additionally, the traditional computing system may be revolutionized with the use of quantum dots. Their ability to convey information from two separates states of zero and one simultaneously has the potential to increase the speed of computing calculations exponentially.

Production of Quantum Dots

There are various possible ways to produce quantum dots, including:

  • Colloidal Synthesis – A process involving transformation of precursors into monomers, which become supersaturated causing the growth of the nanocrystal via nucleation.
  • Fabrication – A method used to create stronger quantum dots with an outer shell.
  • Viral Assembly – Genetically engineered bacteriophage viruses used to form the nanocrystal.
  • Electrochemical Assembly – A method involving an ionic reaction between a metal and an electrolyte, which causes the spontaneous formation of the quantum dot.

References

Further Reading

Last Updated: Apr 28, 2015

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