Take Nanocrystals, Add Boiling Water, and Get a 400-Fold Increase in Luminescence

Just when you were about to throw out those old nanocrystals, a last minute shine from an ultraviolet light reveals previously non-existent luminescence. Is there a word for something that is even more serendipitous than serendipity?

Perhaps we will have to invent one after Prashant Jain, out of habit, put some nanocrystals that he was about to throw out under an ultraviolet light and discovered a significant increase in their luminescence.

Jain, now a chemist with the University of Illinois, was part of a team of researchers led by chemist Paul Alivisatos at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The team was looking at the "cation-exchange" technique for creating core/shell nanocrystals, in which one type of semiconductor is enclosed within another.

While this type of nanocrystal and technique for making them added a new contestant to compete with quantum dots and nanorods synthesized from colloids, they weren’t really impressing with their luminescence.

"While holding promise for the simple and inexpensive fabrication of multi-component nanocrystals, the cation-exchange technique has yielded quantum dots and nanorods that perform poorly in optical and electronic devices," explains Alivisatos in a press release.

But you put those same crystals on the shelf for six months and things change. Upon discovering the change, Jain thought that maybe he could make them change faster by heating the crystals…and it did.

"It was an accidental finding and very exciting," Jain says, "but since no one wants to wait six months for their samples to become high quality I decided to heat the nanocrystals to speed up whatever process was causing their luminescence to increase."

"By heating these nanocrystals to 100 degrees Celsius, we were able to remove the impurities and increase their luminescence by 400-fold within 30 hours," says Jain. "When the impurities were removed the optoelectronic properties of nanocrystals made through cation-exchange were comparable in quality to dots and nanorods conventionally synthesized. "Jain and his colleagues have published their work in the journal Angewandte Chemie under the title "Highly Luminescent Nanocrystals From Removal of Impurity Atoms Residual From Ion Exchange Synthesis".

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Dexter Johnson
Madrid, Spain