Fluorescent Carbon Point Preparation, Performance And Application Research Of Various Light Color Emission

Compared with the traditional fluorescent and organic dyes,carbon dots(CDs)have some unique advantages,including low toxicity,good water solubility,low photobleaching,good biocompatibility and so on.Owing to these merits,more and more attention is paid to carbon dots.However,some of the preparation methods are complex and the quantum yield is not high.The carbon dots which emit in red or even near infrared light are less.So,it is important to use a simple method to synthesize high quantum yield and various light emitted CDs.In the present study,to solve above problems,different preparation methods are used to synthesize high quantum yield CDs.On the one hand,yellowish green luminescent and high quantum yield CDs were prepared by pyrolysis method.On the other hand,various light emitted CDs were synthesized by a facile solvothermal method.The main research contents and conclusions are as follows:1.Yellowish green luminescent and high quantum yield CDs were synthesized through one-step pyrolytic method using citric acid and urea.The structure,morphology,and surface groups of the carbon dots were characterized.CDs are spherical and well dispersed without any aggregation in a narrow size distribution,whose average size is near 5nm.There are a large number of hydrophilic organic groups on the surface of CDs.The quantum yield of CDs reaches 78.3%.CDs show a strong emission at 533 nm with excitation at 291,260,460 nm.CDs exhibits excitation-independent photoluminescence behavior under excitation at 365~465 nm.However,they show excitation-dependent PL behavior under excitation of 465~525 nm.The optimum conditions of preparing CDs also were investigated.Citric acid and urea which the molar ratio is 1:4 were heated at 200 ? for 2 h.At the same time,the change in preparation process also was explored.CDs-precursor were obtained firstly,then the CDs were got.The effects of the pH value,organic solvents,inorganic ions and UV irradiation time on the photo-luminescence properties of C-dots were also analyzed.The results showed that the strong acid and strong alkali environment have great influence on the photo-luminescence properties.CDs solution emit in yellow-green light if the polarity of solvent is strong.The stronger the polarity of solvent is,the higher luminescence CDs solution emit.If the polarity of the solvents is week,CDs solution exhibit blue emission.CDs solution emit no light in polar solvent.CDs also exhibit high salt toleranceand and photostability.It was proved that CDs is low toxicity through the cultivation of algae.It exbitted great effect when the CDs are used in printing,anti-counterfeiting,composite materials and optoelectronic materials.2.Blue,yellow,red CDs were prepared by one-step solvothermal method by using citrazinic acid,thioacetamide and acetamide as raw materials.The particle size of the there CDs is below 5 nm.There are lots of groups on surface of CDs.Blue-CDs with 58.7% quantum yield show a strong emission at 458 nm with an optimum excitation at 354 nm.Yellow-CDs with 34.5% quantum yield show a strong emission at 562 nm with an optimum excitation at 494 nm.Red-CDs with 23.8% quantum yield show a strong emission at 655 nm with an optimum excitation at 621 nm.Blue-CDs and red-CDs exhibits excitation-independent photoluminescence behavior,but yellow-CDs are excitation-independent.The effects of inorganic ions and UV irradiation time on the photo-luminescence properties of there C-dots were also analyzed.CDs exhibit high salt toleranceand,good photostability and low toxicity.They also exbitted great effect when three CDs are used in printing,anti-counterfeiting,composite materials and optoelectronic materials.