Electrical control of single-photon emission in highly charged individual colloidal quantum dots.

Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons with only one or two extra charges have been observed and exploited for very efficient lasing or single-quantum dot light-emitting diodes. Here, by room-temperature time-resolved experiments on individual giant-shell CdSe/CdS quantum dots, we show the electrochemical formation of highly charged excitons containing more than 12 electrons and 1 hole. We report the control over intensity blinking, along with a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase in the decay rate, accompanied by 12-fold decrease in the emission intensity, while preserving single-photon emission characteristics. These results pave the way for deterministic control over the charge state, and room-temperature decay rate engineering for colloidal quantum dot-based classical and quantum communication technologies.

Monitoring plasmonic hot-carrier chemical reactions at the single particle level.

Plasmon excitation in metal nanoparticles triggers the generation of highly energetic charge carriers that, when properly manipulated and exploited, can mediate chemical reactions. Single-particle techniques are key to unearthing the underlying mechanisms of hot-carrier generation, transport and injection, as well as to disentangling the role of the temperature increase and the enhanced near-field at the nanoparticle-molecule interface. Gaining nanoscopic insight into these processes and their interplay could aid in the rational design of plasmonic photocatalysts. Here, we present three different approaches to monitor hot-carrier reactivity at the single-particle level. We use a combination of dark-field microscopy and photoelectrochemistry to track a hot-hole driven reaction on a single Au nanoparticle. We image hot-electron reactivity with sub-particle spatial resolution using nanoscopy techniques. Finally, we push the limits by looking for a hot-electron induced chemical reaction that generates a fluorescent product, which should enable imaging plasmonic photocatalysis at the single-particle and single-molecule levels.