Solution-processable Carbon Dots With Efficient Solid-state Red/Near-Infrared Emission

Carbon dots(CDs)is a new type of luminescent nanomaterials.The unique core structure and the abundant amino,hydroxyl,carboxyl,and other functional groups on the surface endow CDs with unique luminescent properties,great water-soluble ability,low toxicity,and good light stability.As a result,carbon dots have development potential in many research fields,such as optoelectronics,biomedicine,and energy.However,an important problem faced by carbon dots in the development process is that most carbon dots have luminescence in solution,and fluorescence quenching occurs in the solid-state because of the energy transition or the electric non-radiative transition between closing particles.This phenomenon is called aggregation-caused quenching(ACQ).The existence of the ACQ effect greatly limits the development of carbon dots,especially the study of solid-state fluorescent carbon dots.Therefore,the study of solid-state fluorescent carbon dots with the anti-ACQ effect is of great significance.In this article,we used the red-emitting carbon dots synthesized by the previous work of our research group as raw materials to obtain carbon dots with deep red light and near-infrared light emission in the aggregated state by surface modification of branched polymer,followed by characterizing the carbon dots.Preliminary research on its film properties and applications in the field of photoluminescence LED devices and in vivo bioimaging was done i n the end.the specific work is as follows:1.solid-state fluorescent carbon dots(P-CDs)with deep red and nearinfrared emission were synthesized by the solvothermal method using branched polyethyleneimine(b-PEI)and carbon dot precursors as raw materi als.The characterization of P-CDs morphology and chemical structure was studied.2.We characterized the optical physics of P-CDs.The luminescence in the red and near-infrared region of P-CDs could be observed in both solution and solid states.The fluorescence quantum efficiency of the aggregate state was 21%,which was equivalent to the fluorescence quantum efficiency of the solution,proving that the surface modification successfully overcomes the ACQ effect.Notably,It was the first report of the near-infrared fluorescent solid-state carbon dots.The mechanism of the luminescence of the aggregated state of carbon dots was studied by the excited state dynamics characterization.3.We characterized the film-forming properties of P-CDs in different planes.The P-CDs performed great film-forming properties on a hydrophilic substrate and proved their application potential in the field of electroluminescence.After that,we applied P-CDs to the preparation of photoluminescence LED devices.Deep red and white LED devices were obtained easily.The properties of these LED devices w ere also characterized.Finally,using P-CDs as imaging reagents in near-infrared fluorescence imaging in vivo can realize fluorescence imaging of mouse stomach.