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.

Quantum emitters radiate light omni-directionally, making it hard to collect and use the generated photons. Here, we propose a three-dimensional metal-dielectric parabolic antenna surrounding an individual quantum dot as a source of collimated single photons, which can then be easily extracted and manipulated. Our fabrication method relies on a single optically induced polymerization step once the selected emitter has been localized by confocal microscopy. Compared to conventional nanoantennas, our geometry does not require near-field coupling, and it is, therefore, very robust against misalignment issues and minimally affected by absorption in the metal. The parabolic antenna provides one of the largest reported experimental directivities ( D = 106) and the lowest beam divergences (Θ = 13.5°) and a broadband operation over all of the visible and near-infrared range together with extraction efficiency of more than 96%, offering a practical advantage for quantum technological applications.

Charge doping of materials with 2D and 3D quantum confinement is a flexible tool to tailor their excitonic emission. Here, using electron doping experiments on transition metal dichalcogenide (TMD) monolayers, reversible tuning of charged exciton emission within a redshift of up to 75 meV is demonstrated by applying very modest voltages (corresponding roughly to the band gap of TMDs), while also controlling the radiative lifetime and intensity. It is found that the neutral exciton ionization dynamics at increasing electron doping follows the Fermi–Dirac distribution, which allows to determine the size of the band gap as well as to extract experimental values for effective masses of electrons and holes at room temperature. The tunable excitonic emission, preserving coherence at room temperature, holds great promise for quantum technologies requiring deterministic coupling with integrated photonic and plasmonic devices.

Cathodoluminescence spectroscopy in conjunction with second-order auto-correlation measurements of g_2(τ) allows to extensively study the synchronization of photon emitters in low-dimensional structures. Co-existing excitons in two-dimensional transition metal dichalcogenide monolayers provide a great source of identical photon emitters which can be simultaneously excited by an electron. Here, we demonstrate large photon bunching with g_2(0) up to 156±16 of a tungsten disulfide monolayer (WS2), exhibiting a strong dependence on the electron-beam current. To further improve the excitation synchronization and the electron-emitter interaction, we show exemplary that the careful selection of a simple and compact geometry -- a thin, monocrystalline gold nanodisk -- can be used to realize a record-high bunching g_2(0) of up to 2152±236. This approach to control the electron excitation of excitons in a WS2 monolayer allows for the synchronization of photon emitters in an ensemble, which is important to further advance light information and computing technologies.