A Solvent-free Route For The Preparation Of Multicolor Carbon Dots And Their Application In Light Emitting Devices

Carbon dots(CDs),as an environment-friendly material,have attracted much attention of research workers due to their merits,such as low cost,good compatibility,low cytotoxicity and wide range of synthetic materials.At present,the preparation of CDs with long wavelength emission and tunable fluorescence has become the research focus.In this paper,a series of multicolor CDs with excellent fluorescence properties were prepared by solvent-free synthesis method.The physical and chemical properties and morphology of multicolor CDs were characterized by UV-Vis spectrometer,fluorescence spectrometer,transmission electron microscopy(TEM),fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)and Raman spectroscopy(Raman)in detail.The luminescence mechanism of multicolor CDs was also studied.Three CDs emitting blue,green and red light were prepared by solvent free method from phenylenediamine.The three CDs have good dispersibility and contain a variety of functional groups such as-OH,C=N/C=O,-NH and-COOH on the surface.The PL emission peaks of B-CDs,G-CDs and R-CDs are located at 474 nm,500 nm and 704 nm,respectively.Meanwhile,the quantum efficiency of R-CDs can reach 21.96%.FTIR,XPS and XRD analyses show that the different optical characteristics of B-CDs,G-CDs and R-CDs are caused by their different C=O/C=N functional group and graphitized nitrogen content,which eventually leads to the red shift of the emission wavelength of CDs.In addition,a white light-emitting diode(WLED)closing to natural light is prepared.The corresponding color coordinate(CIE)of WLED is(0.33,0.34),which is close to the standard white light.Full-color fluorescent CDs were fabricated by solvent-free method using potassium chloride(KCl)as catalyst and o-phenylenediamine(o-PD)as raw material.By changing the reaction conditions and the amount of potassium chloride,full-color fluorescent CDs with emission wavelength covering 458-615 nm were synthesized.Four typical B-CDs,G-CDs,Y-CDs and R-CDs were characterized.The results show that the prepared CDs have a similar particle size distribution.The quantum yields of B-CDs,G-CDs,Y-CDs and R-CDs are 14.35%,11.88%,13.79% and 12.96%,respectively.The red shift of CDs is related to the graphitization degree and graphitic nitrogen content.In addition,a WLED device with a color coordinate of(0.34,0.33)was prepared by using CDs-polyvinyl alcohol composite material and a 365 nm chip.The emission of the WLED can be extended to the entire visible light region.These results provide some theoretical basis and technical support for the preparation of fullcolor fluorescent CDs and the application of light-emitting devices.The paper has 45 figures,19 tables and 126 references.