Applied Physics

Falling into Traps

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Science  19 Apr 2013:
Vol. 340, Issue 6130, pp. 251
DOI: 10.1126/science.340.6130.251-b

Semiconducting nanocrystals, or quantum dots, are promising materials for use in laser, light-emitting diode (LED), and solar cell applications, partly because of the tunability of their photophysical properties with size. One important size-dependent property in this context is the rate of Auger recombination, a process whereby one or more excited carriers relax through energy transfer to another carrier. Cohn et al. report that, in zinc oxide nanocrystals negatively photodoped under anaerobic conditions, a distinct sort of trap-assisted Auger recombination occurs at a rate that varies as the inverse square of the particle radius. Transient absorption and photo-luminescence spectroscopy reveal the decay rates associated with relaxation of a conduction-band electron to a deep localized hole, through concomitant energy transfer to an extra conduction-band electron. Although the radial rate dependence is shallower than the inverse cube scaling of more widely studied biexciton recombination processes, the authors note that surface traps are common enough for the process to play a significant, and perhaps underappreciated, role in quantum dot photophysics.

Nano Lett. 13, 1810 (2013).

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