Controllable Synthesis And Performance Research Of Fluorescent Carbon Nanodots With High-efficiency

Carbon nanodots?CDs?are one of the hot topics in the field of nano-fluorescence materials with potential applications mainly due to their good bio-compatibility,high water solubility,excellent light stability and low cost.However,the reported CDs showed some problems of low photoluminescence quantum yield?PLQY?,complex synthesis routes,limited luminescent area and fluorescence quenching in solid state,which hinder their further development and application.Therefore,in this paper,CDs were adopted as the research object to study the synthesis,properties and applications of CDs to solve the above mentioned problems.Based on the easy preparation as the purpose,hydrothermal method was chosen as the synthetic way to prepare various CDs.In addition,blue emission CDs with high PLQY,CDs with full color emission and solid CDs with fluorescence non-quenching were respectively synthesized via adjusting different carbon sources,preparation conditions?temperature,concentration and time?and solvent system of hydrothermal reaction.Besides,to provide a basis for the application of CDs in related fields,the relationships among the composition,morphology,functional group,optical property and photoluminescence mechanism of the CDs were investigated and revealed.Finally,the prepared CDs were used in the fields of bio-imaging,fluorescence/magnetic resonance imaging?MRI?dual-mode imaging,ions detection,fluorescence ink and WLED devices,respectively.The details are summarized as follows:1.Firstly,CDs with PLQY as high as 37.4%and 48.5%were prepared via a simple hydrothermal process using green natural raw materials of oatmeal and sesame as precursors,respectively.The optimized products emitted strong blue fluorescence under excitation of 360 nm,showed good bio-compatibility and excellent light stability,and thus exhibited excellent fluorescence imaging effect in bio-imaging.Besides,the CDs derived from sesame showed potential applications in Fe³⁺detection and fluorescence ink.2.Highly blue photo-luminescent Gd³⁺doped CDs?Gd-CDs?with a high PLQY of 69.86%were directly synthesized via a simple hydrothermal treatment by optimizing the reaction temperature,reaction time and concentration of precursors,and using citric acid,diethylenetriamine and GdCl₃ as the carbon source,passivator,and gadolinium source,respectively.Besides,Gd-CDs showed much improved longitudinal relaxivity of 14.33 mM^-1 s^-1 in comparison with commercial Magnevist(4.5 mM^-1 s^-1).Excellent water solubility,good cell-membrane permeability and negligible cytotoxicity make Gd-CDs an ideal dual-modal fluorescence/MR imaging nanoprobe,suggesting its potential and significance in practical biological and clinic applications in the future.3.CDs with full color emission were synthesized by adjusting hydrothermal reaction system?reaction temperature,reaction time and solvent system of hydrothermal reaction?,and using isomers of o/m/p-phenylenediamine as carbon source,respectively.CDs with blue,green,yellow,orange and red emission showed PLQY of 22.48%,39.75%,15.1%,30.28%and 14.9%,respectively.Then,composition,morphology,functional group and fluorescence property of the all prepared CDs were explored to illustrate emission mechanism.Lastly,CDs with blue and green emission showed potential applications in Cr⁶⁺and Al³⁺detection,and detection limit can reach 5.4?g/L and 0.09 mg/L,respectively.Besides,CDs with orange emission showed potential applications in bio-imaging to successfully calibrate HeLa cells.4.Solid CDs with fluorescence non-quenching were synthesized via mixing starch with yellow emission CDs solution by physical and chemical adsorption between them.By optimizing the proportion of starch and CDs?50:1?,hybrid phosphor with high PLQY of 66.9%was obtained.Composition,structure and fluorescence property of the prepared solid CDs were studied in details.The results indicated that starch and CDs can form one core-shell structure,and the CDs absorbed in surface of starch can avoid their agglomeration,thus solving the problem of fluorescence quenching of CDs in solid state.Finally,WLED was fabricated by combining the prepared CDs based phosphor with a blue LED chip,which showed a high CRI of 79.7,luminous efficiency of 39.76 lm/W,color temperature of 8976 K and color coordinates of?0.2817,0.3095?.