1. Department of Chemistry,
2. The Institute of Optics, University of Rochester, Rochester, New York 14627, USA
3. Eastman Kodak Company, Rochester, New York 14650, USA
4. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14583, USA
5. Naval Research Laboratory, Washington DC 20375, USA

Correspondence to: Keith Kahen³Alexander L. Efros⁵Todd D. Krauss^1,2 Correspondence and requests for materials should be addressed to T.D.K. (Email: krauss@chem.rochester.edu), A.L.E. (Email: efros@dave.nrl.navy.mil) or K.K. (Email: keith.kahen@kodak.com).

Abstract

The photoluminescence from a variety of individual molecules¹ and nanometre-sized crystallites² is defined by large intensity fluctuations, known as 'blinking', whereby their photoluminescence turns 'on' and 'off' intermittently, even under continuous photoexcitation². For semiconductor nanocrystals, it was originally proposed³ that these 'off' periods corresponded to a nanocrystal with an extra charge. A charged nanocrystal could have its photoluminescence temporarily quenched owing to the high efficiency of non-radiative (for example, Auger) recombination processes between the extra charge and a subsequently excited electron–hole pair; photoluminescence would resume only after the nanocrystal becomes neutralized again. Despite over a decade of research, completely non-blinking nanocrystals^{4, 5} have not been synthesized and an understanding of the blinking phenomenon⁶ remains elusive. Here we report ternary core/shell CdZnSe/ZnSe semiconductor nanocrystals that individually exhibit continuous, non-blinking photoluminescence. Unexpectedly, these nanocrystals strongly photoluminesce despite being charged, as indicated by a multi-peaked photoluminescence spectral shape and short lifetime. To model the unusual photoluminescence properties of the CdZnSe/ZnSe nanocrystals, we softened the abrupt confinement potential of a typical core/shell nanocrystal, suggesting that the structure is a radially graded alloy of CdZnSe into ZnSe. As photoluminescence blinking severely limits the usefulness of nanocrystals in applications requiring a continuous output of single photons, these non-blinking nanocrystals may enable substantial advances in fields ranging from single-molecule biological labelling⁷ to low-threshold lasers⁸.

1. Department of Chemistry,
2. The Institute of Optics, University of Rochester, Rochester, New York 14627, USA
3. Eastman Kodak Company, Rochester, New York 14650, USA
4. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14583, USA
5. Naval Research Laboratory, Washington DC 20375, USA

Correspondence to: Keith Kahen³Alexander L. Efros⁵Todd D. Krauss^1,2 Correspondence and requests for materials should be addressed to T.D.K. (Email: krauss@chem.rochester.edu), A.L.E. (Email: efros@dave.nrl.navy.mil) or K.K. (Email: keith.kahen@kodak.com).

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