Composite Fabrication And Application Of Multicolor Carbon Dot

Carbon dots（CDs）,as a new generation of fluorescent nanomaterials,have the advantages of wide source of synthetic materials,low cost,excellent optical properties,good biocompatibility and low toxicity.Therefore,They are widely used in LED photoelectric devices,metal ion detection,optical sensors,cell labeling and other fields.However,so far,carbon dots still face many problems:1.Most of the CDs luminescence with high fluorescence quantum efficiency are blue or green with short wavelength,while the high fluorescence quantum efficiency carbon dots located in the long wavelength region（such as yellow light,red light）are less.2.Solid-state carbon dots cause fluorescence quenching due to agglomeration,which seriously hinders the practical application of CDs as fluorescent materials.Therefore,based on the development of CDs,the band gap and energy level of CDs are regulated by doping elements,and the multicolor fluorescent CDs are prepared by adjusting solvent and other conditions.And solid carbon dots are synthesized by matrix coating.Finally,its applications in ion detection,luminescent film,fingerprint identification and photoluminescence devices are realized,as follows:（1）A facile one-pot synthesis of CDs doped S and N element was prepared using theophylline（TH）as the N dopant,Ammonium1-pyrrolidinedithiocarbamate（A1P）as the S dopant mainly and citric acid（CA）as carbon source.By tuning the thermal-pyrolysis temperature and molar ratio of reactants,optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents.Based on the excitation spectrum,emissive spectrum,fluorescence lifetimes,and FT-IR of these CDs,it is proved that the fluorescence of CDs is determined by the different surface states of S and N elements on the carbon core surface.In terms of the applications,blue CDs（B-CDs-1）exhibits high sensitivity for ion detections of Ag⁺and Fe³⁺,which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs.Moreover,blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film,which exhibits stable fluorescence with a CIE coordinate of（0.32,0.33）and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field.In order to obtain long wavelength carbon dots,citric acid（CA）as carbon source and thiourea（TU）as the N dopant were dissolved in the mixed solution of DMF/HCl and DMF/Na OH respectively.The blue,green and red carbon dots were prepared by changing the reaction conditions.However,the fluorescence quenching of solid carbon dots was caused by the aggregation of solid carbon dots.Therefore it is necessary to find new materials to inhibit the fluorescence quenching of solid carbon dots.（2）We present a facile method to synthesize S,N-codoped and Si-coupled solid-state carbon nano dots composites（S,N-CNDs/silica）by one-pot solvothermal route of Citrate（CA）,Thiourea（TU）and（3-aminopropyl）triethoxysilane（APTES）with the assistance of suitable solvent.Leveraging regulating the content of dopant and the volume ratio of H₂O and Et OH solvents,which results in different surface structures of CNDs and CNDs/silica composites during the cross-linked coupling reaction,the PL emissions of resulting composites shifts from blue to olivine to classify into blue,green,olivine corresponding to the fluorescence quantum yields（FLQYs）of 10%,51%,and 9%,respectively.Clearly,the green emitting CNDs/silica composite（G-CNDs/silica）is the highest value,which promises to apply to detect latent fingerprints and fabricate LED devices.The result shows rich details in latent fingerprints can be recognized by the imaging of G-CNDs/silica powder and the WLED device using G-CNDs/silica as green phosphor obtains a very high color rendering index（CRI）of 94.2 at the CIE=（0.34,0.33）.