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Nanomaterials

TiO₂ nanocrystals exhibit unusual slow-motion blinking

Made via template-based synthesis, the defective crystals actively mediate photocatalysis

by Mitch Jacoby
June 13, 2020 | APPEARED IN VOLUME 98, ISSUE 23

 

09823-scicon11-blink.jpg
Credit: Angew. Chem., Int. Ed.
A single TiO2 particle blinks in slow motion, as seen in these micrographs that were recorded with a time delay of roughly 15 s between frames.

Like microscopic fireflies, semiconductor nanocrystals, also known as quantum dots, light up intermittently. For more than 20 years, researchers have worked to understand and control these random fluctuations in light emission because the “blinking” limits the stability of quantum dot–based devices like solar cells and light-emitting diodes. The observation of what may be a new type of blinking behavior suggests that researchers have more work to do (Angew. Chem., Int. Ed. 2020, DOI: 10.1002/anie.202005143). A team led by Tao Zhang, Tewodros Asefa, and Alexei M. Tyryshkin of Rutgers University and Eliška Mikmeková of the Czech Academy of Sciences reports that treating a polymer-derived porous carbon template with a titanium dioxide precursor yields TiO2 nanocrystals—limited to 10 nm in diameter and riddled with oxygen vacancies—that blink in an unprecedented way. In contrast to years of studies reporting rapid light–induced blinking with flashes often lasting just a fraction of a second—sometimes longer—the new work describes electron beam–induced flashes lasting roughly 15 s. In addition, when the crystals are irradiated with light, the resulting charge separation is unusually stable, making the particles active photocatalysts, as shown by tests in which the team used them to reduce carbon dioxide with water.

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