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Pennycook, Timothy J

Publications and source records attributed to Pennycook, Timothy J.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Dynamic fluctuations in ultrasmall nanocrystals induce white light emission

Nanocrystals typically emit monochromatically at their size-dependent energy gaps. Recently, it was found that by pushing the size of a nanocrystal to its lower limits, absorption occurs at increasingly larger energies, but the expected blue to ultraviolet emission does not occur. Instead, individual ultrasmall CdSe nanocrystals emit white light1-5. Here we show that following excitation, partial thermalization sets the ultrasmall nanocrystals into a fluxional6 state, with a continuously varying energy gap which results in white light emission. Even the larger, monochromatic nanocrystals have a fluxional surface but a stable crystal core. A degree of fluxionality persists even at room temperature and represents a radical change to the accepted view of nanocrystals, with wide-ranging ramifications for other applications. The results were obtained using a combination of state-of-the-art experiment and theory: dynamic imaging by aberration-corrected scanning transmission electron microscopy and finite-temperature quantum molecular dynamics simulations. The results show that small is different, but ultrasmall is different yet again.

Pennycook, Timothy J↗