We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.

Two-photon fluorescence materials have attracted much recent attention for their many promising applications, especially in the growing field of biomedical imaging. 1-5 Among the best performing two-photon fluorescence materials are semiconductor quantum dots such as CdSe and related core-shell nanoparticles. 6-8 These quantum dots have been demonstrated in various optical imaging experiments in vitro and in vivo. 6,9,10 At the same time, however, heavy metals as the essential elements in available high-performance semiconductor quantum dots have prompted serious health and environmental concerns in the community and beyond. Therefore, the search for benign alternatives has become increasingly important and urgent. Recently, we found and reported 11 that nanosized pure carbon particles may be surfacepassivated to exhibit bright photoluminescence in the visible. These photoluminescent carbon dots (C-Dots, Figure 1a) are of two distinctive features: one is that the underlying carbon particles are very small (sub-10 nm); and the other is that the particle surface is passivated by organic or other molecules via either covalent linkages or chemical adsorption. 11 Mechanistically, the carbon-based photoluminescence has been attributed to passivated defects on the carbon particle surface acting as excitation energy traps. 11,12 Here we report that the C-Dots also exhibit strong luminescence with two-photon excitation in the near-infrared. The estimated two-photon absorption cross-sections of the C-Dots are comparable to those of available high-performance semiconductor quantum dots. In addition, the two-photon luminescence microscopy imaging of the C-Dots internalized in human cancer cells is demonstrated.

A successful attempt in the functionalization and solubilization of boron nitride nanotubes is reported, and a functionalization mechanism based on interactions of amino functional groups with nanotube surface borons is proposed.

Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future.

This paper reports the facile synthesis of a unique interleaved expanded graphite-embedded sulphur nanocomposite (S-EG) by melt-diffusion strategy. The SEM images of the S-EG materials indicate the nanocomposites consist of nanosheets with a layer-by-layer structure. Electrochemical tests reveal that the nanocomposite with a sulphur content of 60% (0.6S-EG) can deliver the highest discharge capacity of 1210.4 mAh g À1 at a charge-discharge rate of 280 mA g À1 in the first cycle, the discharge capacity of the 0.6S-EG remains as high as 957.9 mAh g À1 after 50 cycles of charge-discharge. Furthermore, at a much higher charge-discharge rate of 28 A g À1 , the 0.6S-EG cathode can still deliver a high reversible capacity of 337.5 mAh g À1 . The high sulphur utilization, excellent rate capability and reduced overdischarge phenomenon of the 0.6S-EG material are exclusively attributed to the particular microstructure and composition of the cathode.

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The detection of nanotube carbons in solution by (13)C NMR is reported. The highly soluble sample was from the functionalization of (13)C-enriched single-walled carbon nanotubes (SWNTs) with diamine-terminated oligomeric poly(ethylene glycol) (PEG(1500N)). The ferromagnetic impurities due to the residual metal catalysts were removed from the sample via repeated magnetic separation. The nanotube carbon signals are broad but partially resolved into two overlapping peaks, which are tentatively assigned to nanotube carbons on semiconducting (upfield) and metallic (downfield) SWNTs. The solid-state NMR signals of the same sample are similarly resolved. Mechanistic and practical implications of the results are discussed.

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