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Blinking semiconductor nanorods

Physicists at the University of Pennsylvania have shown that when semiconductor nanorods are exposed to light their combined "on" time is increased dramatically providing new insight into this mysterious blinking behavior. When provided with energy, whether in the form of light, electricity or certain chemicals, many semiconductors emit light. This principle is at work in light-emitting diodes, or LEDs, which are found in any number of consumer electronics. But when semiconductors are made to nanometer size, instead of shining steadily, they turn "on" and "off" in an unpredictable fashion, switching between emitting light and being dark for variable lengths of time. For the decade since this was observed, many research groups around the world have sought to uncover the mechanism of this phenomenon, which is still not completely understood.

Researchers claim that these nanorods can be 'on' and 'off' for all scales of time, from a microsecond to hours and the researchers have shown that clustering these nanorod semiconductors greatly increases their total "on" time and any further addition of a rod to the cluster increases the "on" period of the group when nanorods are very close together.

This effect was demonstrated by depositing cadmium selenide nanorods of 5-nanometer onto a substrate, shining a blue laser on them, then red light was observed.The nanorod clusters can be as small as two and as large as 110, but when high in number the cluster effectively exhibits macro scale properties and stops blinking entirely.The exact mechanism that causes this prolonged luminescence was attributed to the interactions between electrons in the cluster.As nanorods can be an order of magnitude smaller than a cell, but can emit a signal that can be relatively easily seen under a microscope, they have been long considered as potential biomarkers. Their inconsistent pattern of illumination, however, has limited their usefulness. If the emission time of semiconductor nanocrystals could be extended to many minutes it makes them much more usable even as fluorescent labels.

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