Controllable Preparation And Application Of Multicolor Luminescent Carbon Dot

Multicolor carbon dots(MCDs),as a novel carbon-based fluorescent nanomaterial,have attracted much attention due to their excellent biocompatibility,tuneable photoluminescence(PL),high quantum yield and unique electronic and physicochemical properties,and have been widely used in the fields of biological imaging,light-emitting diodes,sensing,and anti-counterfeiting.In recent years,researchers have been looking for suitable preparation,modification,or functionalization methods to regulate the luminescence properties of carbon dots.The strategies include changing the carbon precursors,reaction conditions(such as temperature,time,precursor ratio,etc.),reaction environment(solvent,p H,etc.),post-treatment(column chromatography separation,etc.),or others(excitation wavelength,concentration,pressure,etc.).However,because the luminescence mechanism of carbon dots varies with different synthesis methods or carbon precursors,there is no rules to follow to prepare multicolor carbon dots,especially red carbon dots.Therefore,how to regulate the structure and fluorescence property of carbon dots by effective and systematic synthesis methods is still an urgent problem to be solved.In view of this,in this paper,according to the photoluminescence mechanism of multicolor carbon dots,the controllable preparation of multicolor carbon dots can be realized by selecting appropriate carbon precursors or reaction conditions.By summarizing the luminescence rules of multicolor carbon dots,the size and graphite N content of carbon dots play important roles in regulating the fluorescence of CDs.The prepared multicolor carbon dots can realize the quantitative detection of p H and show potential application in biological imaging and solid-state luminescence.The research work are as follows:(1)The synthesis of red,yellow and blue carbon dots and their application as solid state luminescent materials in LED.Multicolor fluorescent carbon dots with red(R-CDs),yellow(Y-CDs),and blue(BCDs)emissions were prepared by choosing proper aromatic precursors with different amounts of benzene rings through a simple solvothermal method.The characterization showed that the prepared carbon dots were spherical with a size under 10 nm,rich surface functional groups,and good stability.The emission wavelengths were located at 440,530,and 580 nm under the excitation of 370 nm.The relative fluorescence quantum yield(QY)of MCDs was 11%,59%,and 33%,respectively.The related characterization demonstrated that the redshift in the photoluminescence was caused by the synergistic effect of the increasing graphitic nitrogen content,quantum size effect and surface oxidation state.By mixing the three prepared CDs into a PVA matrix,the transparent and flexible films produced relucent blue,yellow,and red emissions under 365 nm UV light,and solid-state quenching was effectively avoided.LEDs were fabricated by using B-CDs,Y-CDs,and RCDs/PVA with a semiconductor chip.These CDs-based LEDs produced bright blue,yellow,and red light with CIE color coordinates of(0.16,0.02),(0.38,0.58),and(0.50,0.49)were successfully manufactured utilizing the prepared MCDs as the solid luminescent materials.The results showed that the synthesized CDs can be potentially applied in multi-color monitors as a promising candidate for light-emitting diodes(LEDs).This work blazes a novel trail for the controllable preparation of multicolor fluorescent carbon dots.(2)Acid-regulated polychromatic luminescent carbon dots and their applications in p H sensing and cell imaging.In this work,by using basic fuchsin as carbon source,nitric acid,and water as reaction medium,multicolor carbon dots with blue,yellow and red luminescence were successfully prepared via regulating the acidity of the reaction environment.In this reaction process,the carbonization,surface modification and nitrogen doping of multicolor carbon dots were realized by a simple one-step hydrothermal method.The detailed characterization showed that the prepared carbon dots were abundant in hydroxyl,carboxyl,amino,pyrrolidine,pyridine and graphite nitrogen groups.These rich functional groups endowed MCDs with excellent water solubility and high reactivity.At 380 nm excitation,the emission wavelengths of the three carbon dots were 445,535 and 610 nm,respectively,and the quantum yield(QY)was 21%,50% and 46%,respectively.Further experiments showed that the luminescence characteristics of the synthesized multicolor carbon dots depend on the quantum size effect and graphitization effect.Meanwhile,a linear relationship can be obtained between emission wavelength and particle size,and emission wavelength redshifted with the increase of conjugate area.Subsequently,the multicolor carbon dots were successfully applied to He La cell imaging,with excellent imaging effect and low cytotoxicity.At the same time,the fluorescence emission intensity of the yellow luminescent carbon dots also showed a strong p H dependence.In the range of p H 2.0-12.0,the fluorescence intensity decreases with the increase of p H.By utilizing this property of Y-CDs,the in vitro p H sensing had been successfully realized,which showed a promising application in the detection of intracellular p H.