Air-induced fluorescence bursts from single semiconductor nanocrystals

We observe a dramatic enhancement of the fluorescence intensity from single core∕shell $\mathrm{CdSe}∕\mathrm{ZnS}$ nanocrystals upon sudden exposure to air from an evacuated surrounding. Both the number of particles contributing to emission increases as well as the average emission intensity from a single particle, leading to an overall fluorescence rise by a factor of 60. A common power-law distribution of both on- and off times of single nanocrystals is observed independent of shell thickness and environment. We propose that electron transfer to oxygen, which is facilitated by the presence of water, leads to a neutralization of charged, nonemissive nanocrystals.