Nature Nanotech. 8, 206–212 (2013)

Fluorescence intermittency, also known as blinking, has hampered the use of semiconductor colloidal nanocrystals as reliable photon sources. Several detrimental blinking mechanisms, such as the Auger process that involves a non-radiative energy transfer from a photoexcited electron–hole pair to a third charge, contribute to lowering the efficiency of nanocrystals. Javaux et al. now demonstrate that the Auger process can be deactivated by controlling the temperature of these colloidal nanoemitters. CdSe nanocrystals surrounded by a thick CdS shell preserve a charged negative state when their temperature is lowered from 300 K to 30 K. Nevertheless, the presence of such charge does not affect radiative recombination below 200 K. Indeed, the small energy offset in the conduction band and the confinement of charges in these structures are tuned by temperature; only above 200 K can electrons delocalize in the shell and interact with the sharp potential of the outer surface, a necessary condition to activate the Auger process. The importance of energy-band engineering for the synthesis of highly efficient nanocrystals is further demonstrated.