High photoluminescence quantum yield, easily tuned emission colors, and high color purity of perovskite nanocrystals make this class of material attractive for light source or display applications. Here, green light-emitting devices (LEDs) were fabricated using inorganic cesium lead halide perovskite nanocrystals as emitters. By introducing a thin film of perfluorinated ionomer (PFI) sandwiched between the hole transporting layer and perovskite emissive layer, the device hole injection efficiency has been significantly enhanced. At the same time, PFI layer suppressed charging of the perovskite nanocrystal emitters thus preserving their superior emissive properties, which led to the three-fold increase in peak brightness reaching 1377 cd m(-2). The full width at half-maximum of the symmetric emission peak with color coordinates of (0.09, 0.76) was 18 nm, the narrowest value among perovskite based green LEDs.

Nitrogen-doped carbon dots synthesized from citric acid as a carbon precursor have recently been considered to contain fluorescent derivatives of citrazinic acid, which contribute to their emission in the blue spectral range. To study the impact of such molecular fluorescent species on the optical properties of carbon dots, we synthesized three samples employing citric acid and three different nitrogen sources: ethylenediamine, hexamethylenetetramine, and triethanolamine. On the basis of the analysis of the nitrogen content and its coordination by X-ray photoelectron spectroscopy, FTIR spectra, and systematically comparing absorption, steady-state emission, and photoluminescence decays of each kind of carbon dot, we derive the influence of the molecular precursors and gain further understanding of the complex structure of carbon dots highlighting the strong impact of molecular fluorescence in the samples produced with ethylenediamine and hexamethylenetetramine.

Carbon dots (CDs) have attracted rapidly growing interest in recent years due to their unique and tunable optical properties, the low cost of fabrication, and their widespread uses. However, due to the complex structure of CDs, both the molecular ingredients and the intrinsic mechanisms governing photoluminescence of CDs are poorly understood. Among other features, a large Stokes shift of over 100 nm and a photoluminescence spectrally dependent on the excitation wavelength have so far not been adequately explained. In this Letter we investigate CDs and develop a model system to mimic their optical properties. This system comprised three types of polycyclic aromatic hydrocarbon (PAH) molecules with fine-tuned concentrations embedded in a polymer matrix. The model suggests that the Stokes shift in CDs is due to the self-trapping of an exciton in the PAH network. The width and the excitation dependence of the emission comes from a selective excitation of PAHs with slightly different energy gaps and from energy transfer between them. These insights will help to tailor the optical properties of CDs and help their implementation into applications, e.g., light-emitting devices and biomarkers. This could also lead to "artificial" tunable carbon dots by locally modifying the composition and consequently the optical properties of composite PAH films.

The knowledge gap on how different types of nitrogen centers affect the optical properties of N-doped carbon dots (CDs) hinders the rational design and synthesis of these nanostructures. We present a systematic theoretical study of 1 nm small CD models containing nitrogen and oxygen functional groups designed to explore the effects of various nitrogen centers on the absorption characteristics of CDs. Graphitic nitrogen is shown to have an electron-doping effect that alters the systems’ electronic energy levels and causes pronounced red-shift of their absorption spectra. Other kinds of nitrogens including pyridinic, pyrrolic, and amino centers had no appreciable effects on the CDs’ absorption properties.

We review the effect of doping on the optical properties of luminescent colloidal carbon dots. They are considered as a hybrid material featuring both molecular and semiconductor-like characteristics, where doping plays an important role. Starting from the short overview of synthetic strategies, we consider the evolution of carbon dots from molecular precursors to fluorescent nanoparticles, and the relevant structural properties of carbon dots. Choice of the reactant materials, dopant atoms and reaction parameters provide carbon dots with varying optical properties. High chemical stability, bright luminescence and customizable surface functionalization of carbon dots open their use in a broad range of applications, which are exemplary presented at the end of this review.