科研之友
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摘要
The photoluminescence from a variety of individual molecules(1) and nanometre-sized crystallites(2) is defined by large intensity fluctuations, known as ';blinking';, whereby their photoluminescence turns ';on'; and ';off'; intermittently, even under continuous photoexcitation(2). For semiconductor nanocrystals, it was originally proposed(3) 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 phenomenon(6) 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 labelling(7) to low-threshold lasers(8).
- 出版日期2009-6-4
