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Semiconductor nanoplatelets exhibit spectrally pure, directional fluorescence. To make polarized light emission accessible and the charge transport effective, nanoplatelets have to be collectively oriented in the solid state. We discovered that the collective nanoplatelets orientation in monolayers can be controlled kinetically by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. Our method avoids insulating additives such as surfactants, making it ideally suited for optoelectronics. The monolayer films with controlled nanoplatelets orientation (edge-up or face-down) exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Furthermore, we unveil that the substantial in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer, with an efficiency that strongly depends on the orientation of the nanoplatelets. The ability to kinetically control the assembly of nanoplatelets into ordered monolayers with tunable optical and electronic properties paves the way for new applications in optoelectronic devices.

Two-photon polymerization stereolithographic three-dimensional (3D) printing is used for manufacturing a variety of structures ranging from microdevices to refractive optics. Incorporation of nanoparticles in 3D printing offers huge potential to create even more functional nanocomposite structures. However, this is difficult to achieve since the agglomeration of the nanoparticles can occur. Agglomeration not only leads to an uneven distribution of nanoparticles in the photoresin but also induces scattering of the excitation beam and altered absorption profiles due to interparticle coupling. Thus, it is crucial to ensure that the nanoparticles do not agglomerate during any stage of the process. To achieve noninteracting and well-dispersed nanoparticles on the 3D printing process, first, the stabilization of nanoparticles in the 3D printing resin is indispensable. We achieve this by functionalizing the nanoparticles with surface-bound ligands that are chemically similar to the photoresin that allows increased nanoparticle loadings without inducing agglomeration. By systematically studying the effect of different nanomaterials (Au nanoparticles, Ag nanoparticles, and CdSe/CdZnS nanoplatelets) in the resin on the 3D printing process, we observe that both, material-specific (absorption profiles) and unspecific (radical quenching at nanoparticle surfaces) pathways co-exist by which the photopolymerization procedure is altered. This can be exploited to increase the printing resolution leading to a reduction of the minimum feature size.

Hypothesis Carbon dot systems are highly surface sensitive fluorescent nanomaterials. In the presence of specific molecules or ions, the fluorescence properties can be strongly influenced. Often their fluorescent properties are activated or strongly enhanced through passivation agents such as polymer coatings. While several passivating polymers have been directly attached to the carbon dot systems, the interaction of carbon dot systems with the polymer surface of colloids has not been investigated as a way to activate or enhance the photoluminescent properties. Here, we show for the first time that the interaction of carbon dot systems with polymer colloids can strongly enhance the fluorescent properties of the carbon dot systems. Experiments To introduce carbon dot – polymer nanoparticle interactions, carbon dots are either generated directly in a microwave assisted synthesis in the presence of negatively charged polystyrene nanoparticles (in situ) or synthesized in the microwave separately and mixed afterwards with polymer nanoparticles (mixing). For the carbon dot system synthesis, chitosan, 1,2-ethylenediamine, and acetic acid are used as precursors. The produced carbon dot – polymer nanoparticle system are characterized by scanning electron microscopy, transmission electron microscopy, and flow cytometry measurements, and their interaction is assessed by fluorescence spectroscopy and fluorescence lifetime measurements. Findings We show that depending on the synthesis route (in situ or mixing), the carbon dot systems are either covalently attached (in situ) or electrostatically bound (mixing) to the surface of the nanoparticles. Regardless of the preparation methods of the investigated carbon dot – polymer nanoparticle system and the interaction (chemical or physical) with the surface, the fluorescence intensity is strongly enhanced and the fluorescence lifetime prolonged. These findings indicate a stabilization of the radiative trap states of carbon dot systems through interaction with the surface of the particles.

Crystalline first-row transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) ferrites were prepared by an unprecedented synergetic combination of miniemulsion synthesis and solvothermal route, pursuing unconventional conditions in terms of space confinement, temperature, and pressure. This synergy allowed for obtaining six different crystalline ferrites at much lower temperature (i.e., 80 °C) than usually required and without any postsynthesis thermal treatment. X-ray diffraction (XRD) revealed that analogous ferrites synthesized by miniemulsion at ambient pressure or in bulk (i.e., from an aqueous bulk solution and not in the confined space of the miniemulsion droplets) either at ambient pressure or under solvothermal conditions did not result in comparatively highly crystalline products. To follow the structural evolution at local level as a function of reaction time and depending on the synthesis conditions, X-ray absorption spectroscopy (XAS) was used to determine the cation distribution in these structures. Well-defined nanostructures were observed by transmission electron microscopy (TEM). Concerning their functional behavior, the synthesized ferrites presented superparamagnetism and were found to be active oxidation catalysts, as demonstrated for the oxidation of styrene, taken as a model reaction. Because of the magnetic properties, the ferrites can be easily recovered from the reaction medium, after the catalysis, by magnetic separation and reused for several cycles without losing activity.