Dynamic fluctuations in ultrasmall nanocrystals induce white light emission

Journal Article · Sun Jan 01 00:00:00 EST 2012 · Nano Letters

DOI:https://doi.org/10.1021/nl3008727· OSTI ID:1055011

Pennycook, Timothy J ^[1]; Mcbride, J. R. ^[2]; Rosenthal, Sandra ^[2]; Pennycook, Stephen J ^[1]; Pantelides, Sokrates T. ^[2]

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1. ORNL
2. Vanderbilt University

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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1055011
• Journal Information: Nano Letters, Vol. 12, Issue 6; ISSN 1530--6984
• Country of Publication: United States
• Language: English