Light emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago. A barrier to the widespread utilization of luminescent silicon nanocrystals in such diverse application areas as optoelectronics, solid-state lighting for general illumination, or fluorescent agents for biological applications has been the lack of a simple, high-yield synthesis approach. Here we report a scaleable single-step synthesis process for luminescent silicon nanocrystals based on a low-pressure nonthermal plasma.

Silicon nanocrystals with diameters of less than 5nm show efficient photoluminescence at room temperature. For ensembles of silicon quantum dots, previous reports of photoluminescence quantum yields have usually been in the few percent range, and generally less than 30%. Here we report the plasma synthesis of silicon quantum dots and their subsequent wet-chemical surface passivation with organic ligands under strict exclusion of oxygen. Photoluminescence quantum yields exceeding 60% have been achieved at peak wavelengths of about 789nm.

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We study ultrafast photoluminescence (PL) dynamics of Si nanocrystals (NCs). The early-time PL spectra (<1 ns), which show strong dependence on NC size, are attributed to emission involving NC quantized states. The PL spectra recorded for long delays (>10 ns) are almost independent of NC size and are likely due to surface-related recombination. Based on instantaneous PL intensities measured 2 ps after excitation, we determine intrinsic radiative rate constants for NCs of different sizes. These constants sharply increase for confinement energies greater than approximately 1 eV indicating a fast, exponential growth of the oscillator strength of zero-phonon, pseudodirect transitions.

The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of fg = 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches fCu ≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, fg = 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm−1K−1 is achieved in composites with binary fillers of fg = 40 wt% and fCu = 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.

convert infrared light into the visible range are desirable as they can enable advanced schemes for photocatalysts 1 , solar energy harvesting 2 , deep tissue imaging 3 and phototherapy 4. Inorganic nanocrystals (NCs) functionalized with energy-accepting dyes form a promising platform to meet this demand. These materials achieve light upconversion by using photons absorbed by the NC to excite spin-triplet excitons centred on organic molecules tethered to their surface 5-7. Pairs of these excitons can merge through a process known as triplet fusion to produce high-energy spin-singlet states that emit visible light. Although upconversion efficiencies of >10% have been achieved by this approach 8,9 , these systems have exclusively employed NCs containing toxic heavy elements such as cadmium or lead (refs. 5,6,10), limiting their range of utility. Replacement of these NCs with nontoxic infrared absorbers is a key step in designing upconversion systems suitable for both biological and environmental applications.

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The influence of the dielectric barrier on the discharge regime of a uniform atmospheric pressure glow discharge is studied through fast, time-resolved imaging of the discharge optical emission and by a one-dimensional fluid model. The experiments show that the discharge regime can be adjusted over a wide range from a glow-like regime with a pronounced Faraday dark space and positive column to a Townsend-like discharge regime in which those features are absent. The determining factor for the discharge regime is the current limitation through the dielectric. Results of the one-dimensional fluid model confirm this observation. The fluid model also indicates that metastable helium atoms generated during a discharge pulse contribute significantly to the pre-ionization of the gas before the next breakdown through Penning ionization of nitrogen impurities.