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Research: Precise tuning of quantum dot emissions

Posted: 06 Jun 2013 ?? ?Print Version ?Bookmark and Share

Keywords:quantum dots? biomedical monitoring system? solid-state lighting? flat-panel display?

A team of researchers at Massachusetts Institute of Technology (MIT) has found a way to make quantum dots even more efficient at delivering precisely tuned colours of light. Tiny particles of matter called quantum dots, which emit light with exceptionally pure and bright colours, are presently being used as biological markers, and has the potential to be used in computer and TV screens, and solid-state lighting.

These materials, called colloidal semiconductor quantum dot nanocrystals, can emit any colour of light, depending on their exact size or composition. But there is some variability in the spread of colours that different batches of nanocrystals produce, and until now there has been no way to tell whether that variability came from within individual particles or from variations among the nanocrystals in a batch. That's the puzzle an MIT team has now solved, presented in a paper by chemistry professor Moungi Bawendi, graduate student Jian Cui and six others.

For many applicationssuch as flat-panel displaysit's important to make particles that emit a specific, pure colour of light. So, it's important to know whether a given process produces nanocrystals with an intrinsically narrow or broad spectrum of colour emission.

"You need to understand how the spectrum of a single particle relates to the spectrum of the whole ensemble," Cui said. But existing observational methods that detect an entire ensemble produce data that "is blurring the information," and methods that attempt to extract data from single particles have limitations.

The new method, developed in Bawendi's lab, is a radical departure from conventional means of observing light emissions from single emitters. Normally, this is done by isolating individual emitters, stabilising them on a substrate, and observing them one at a time.

But this approach has two drawbacks, Bawendi added: "You only get small numbers, because you're looking at one at a time, and there's a selection bias, because you usually look at the bright ones."

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