Aqueous dispersions of graphene oxide (GO) have been found to emit a structured, strongly pH-dependent visible fluorescence. Based on experimental results and model computations, this is proposed to arise from quasi-molecular fluorophores, similar to polycyclic aromatic compounds, formed by the electronic coupling of carboxylic acid groups with nearby carbon atoms of graphene. Sharp and structured emission and excitation features resembling the spectra of molecular fluorophores are present near 500 nm in basic conditions. The GO emission reversibly broadens and red-shifts to ca. 680 nm in acidic conditions, while the excitation spectra remain very similar in shape and position, consistent with excited state protonation of the emitting species in acidic media. The sharp and structured emission and excitation features suggest that the effective fluorophore size in the GO samples is remarkably well defined.

Here we report an approach to roll out Li-ion battery components from silicon chips by a continuous and repeatable etch-infiltratepeel cycle. Vertically aligned silicon nanowires etched from recycled silicon wafers are captured in a polymer matrix that operates as Li þ gel-electrolyte and electrode separator and peeled off to make multiple battery devices out of a single wafer. Porous, electrically interconnected copper nanoshells are conformally deposited around the silicon nanowires to stabilize the electrodes over extended cycles and provide efficient current collection. Using the above developed process we demonstrate an operational full cell 3.4 V lithium-polymer silicon nanowire (LIPOSIL) battery which is mechanically flexible and scalable to large dimensions.polymer electrolyte | core-shell nanowires | energy storage | flexible electronics | waste management S ilicon is a promising anode material in lithium batteries due to its high specific capacity and low operation voltage (1). However, the major concern in using Si-based anodes is the huge volume expansion during the lithiation that leads to a fast degradation of the electrode material and a reduced life cycle of the battery with limited use in real life Li-ion applications. The advent of nanotechnology and successful incorporation of nanostructured materials in energy storage devices has further grown an interest in revisiting Si as an active anode material. The enhancement in the electrochemical performance of nanostructured Si anodes provides novel platforms for the ubiquitous presence of Si in Li-ion batteries (2-4). Through nanostructuring, the active Si pulverization was minimized yielding stable capacity retention. However, this was found insufficient to maintain a uniform electrical interface and adequate mechanical contact between the active Si particles and the conductive additives, calling for the development of new binder materials (5-7). Avoiding binders or conductive additives and enabling a direct contact between Si and the current collector is the other way to maintain the electrical conductivity and mechanical integrity of the electrode. This requires special designs of the current collector complying with the ensuing active material deposition. The optimal alternative so far is provided by the use of nanowires, nanotubes, or hierarchical assemblies directly grown, assembled, or bonded onto the current collector (8-12).Current collectors integrated with Si anodes have been successfully fabricated through chemical or physical vapor deposition methods, room temperature metal assisted chemical etching (MACE), as well as through various top-down methods (8,9,(12)(13)(14)(15). One of the major drawbacks of the respective configurations is the relatively low tap density of the Si nanostructures leading to low mass loading of active material and low volumetric capacities. Moreover, excess of current collector is usually employed in this configuration rendering them less attractive for high-throughput battery manufacturing (16). Low compactio...

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