Synthesis Of Concentration-Dependent Multicolor Carbon Dots And Their Applications In LED

Fluorescent carbon dots（C Ds）have many advantages such as wide source of raw materials,easy synthesis,low toxicity,wide range of adjustable spectrum and high stability.CDs are one of the members of the large family of carbon-based nanoluminescent materials.However,there are still the following problems in the study of CDs:First,traditional CDs has a serious aggregation-induced fluorescence quenching phenomenon,which greatly limits its application in the field of light-emitting devices.Second,the fluorescence emission mechanism is unclear and there is still a lack of unified cognition.Thirdly,the long-term operation of white LED applications is faced with problems such as color deviation and luminous drift,which seriously restrict the further development and application of CDs.Therefore,it is of great scientific significance and value to carry out research on the above problems.In this paper,a series of novel CDs without fluorescence quenching were synthesized by high temperature microwave reaction with different amino acids using citric acid as carbon source precursor.The fluorescence of C Ds was continuously adjustable in the full spectral range.Combined with structural analysis and theoretical calculation,the luminesce nce mechanism of CDs was studied.Finally,a variety of monochromatic LED and high-quality white LED were prepared by combining CDs with LED of different concentrations.The main research contents and achievements of this paper are as follows:1.A new type of fluorescent CDs was prepared.The CDs is concentration-dependent and the emission spectrum is continuously adjustable in the full visible spectrum.C Ds was further studied by TEM,SEM,AFM,XRD,XPS,FT-IR,UV-Vis,PL,QY and other characterization techniques The results show that the prepared CDs are rich in carboxyl group and has graphite nitrogen structure.By adjusting the surface structure and graphite nitrogen content of CDs,the peak emission position of CDs can be extended from blue light to red light.The graphite nitrogen content of CDs are closely related to its concentration.Therefore,polychromatic fluorescent CDs in the full visible spectral range can be obtained by adjusting the concentration.2.Through relevant theoretical calculation,the results indicate that the effective band gap(Ε₂))changes caused by graphite nitrogen and carboxyl groups on the surface of CDs,and the change of band gap is the main reason for the continuous tunable luminescence of CDs in the full visible spectrum.3.Six kinds of monochrome LED and three kinds of cold white,positive white and warm white LED with high color rendering index were prepared by combining various concentrations of CDs as luminescent conversion layers with 405 nm LED.The color gamut area of each monochromatic LED reached 91.76%of that of the National Television Standards Board（NTSC）,the color rendering index of cold white,positive white and warm white LED reached 90.1,93.4 and 90.6,respectively.It clarifies that the CDs prepared in this paper has important potential application value in monochrome and white light source.