Quantum dots generally refer to specially fabricated nanocrystals that exhibit unique electrical and optical properties due to their inherent quantum properties. However, conventional technology has limited quantum dots to toxic and costly metals as raw materials.

A new study has found a cheaper, safer alternative material that could be further purified to replace toxic metal quantum dots with the same efficiency in various applications.

While there have been prior studies on finding non-toxic and more cost-effective alternatives, these proposed quantum dots emit less light when exposed to ultraviolet (UV) light. In the new study, titled "Ultrafast nanometric imaging of energy flow within and between single carbon dots" and published in the National Academy of Sciences' latest Proceedings, researchers detail how ultrafast nanometric imaging has revealed clusters of good and bad emitters in entire populations of carbon dots. Researchers suggest that by selecting only the good "super-emitters," they can use carbon nanodots as a better alternative.

Quantum Dots
(Photo: Marc Vidal via Wikimedia Commons)
Quantum dots illuminating under UV light exposure

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Carbon Nanodots: The Future of Quantum Dots

Researchers from the University of Delaware, Baltimore County, and the University of Illinois Urbana - Champaign worked on the study through the Beckman Institute for Advanced Science and Technology at Illinois.

"Coming into this study, we did not know if all carbon dots are only mediocre emitters or if some were perfect and others were bad," said Martin Gruebele, a chemistry professor from Illinois who also led the study. He adds that should they demonstrate the existence of good and bad carbon nanodots; there might emerge a method for choosing which ones to use as quantum dots in the future.

To see the good ones from the bad, Gruebele noted that the first step is to observe these carbon nanodots. This is particularly challenging since these are materials less than 10 nanometers in diameter. When excited, this could only emit light in the range of picoseconds, or one-trillionth of a second.

Capturing Good Carbon Nanodots in the Flesh

"Using our previously developed single-molecule absorption scanning tunneling microscope, we could only image excited states with no time resolution," Gruebele explains. He further adds that in their study, they can now record quantum dots still in their excited state by combining two technologies: true nanometer space resolution and femtosecond time resolution.

With these technologies, researchers found out that the energy excitation leads to one of two possible outcomes: either the carbon nanodots emit light themselves or release the received energy as heat before the nanodots light up.

In a given population of these small materials, researchers report that about twenty percent of these carbon nanodots are "perfect emitters." In comparison, the rest - 80 percent of them - only have a very short light emission state before giving the energy off as heat.

"Being able to see that there are different populations tells us that it may be possible to purify carbon dot populations by selecting only the perfect light emitters," Gruebele notes.

Existing metal quantum dots are used in the field of science and medicine as a precise way of checking the health of living cells. Having a safe, non-toxic, and cost-effective option will be a great advancement in the field.


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