Studies On Multicolor Modulation And Performance Of Fluorescent Carbon Dots

As a new type of fluorescent nanomaterial,carbon dots(CDs)have attracted much attention since its discovery.Compared with traditional fluorescent materials,the advantages of non-toxicity,plentiful raw material,various preparation methods and good fluorescence performance make fluorescent CDs spread rapidly in multi-domain applications.In recent years,the research results of CDs have emerged in an endless stream,from single blue fluorescence to multi-color or even full-spectrum visible light fluorescence.The development of various preparation methods has improved the fluorescence quantum yield of CDs that is equal to semiconductor quantum dots and perovskites.However,many problems on the preparation of multi-color CDs are also a major obstacle to the widespread application.How to determine the relationship between structure and fluorescence properties,and establish a multi-color fluorescence emission mechanism have become a research hotspot,which has important guiding significance for accelerating the application of carbon dots.Based on the above problems,this paper mainly explores two routes from multi-color synthesis and light-emitting diode(LED)applications to develop experimental protocols.First,we changed the preparation conditions to explore the influence on the structure and fluorescence properties of carbon dots.And preparing a variety of fluorescent emission CDs to explore the relationship and mechanism of multi-color fluorescence structure.Finally,the preparation of carbon-based fluorescent composite materials and light-conversion LEDs.The specific work content and results are as follows:(1)The CDs were prepared by one-step solvothermal method under different conditions,and the relative fluorescence quantum yield was up to 33.4%.The optimal excitation wavelength is 340 nm and the fluorescence emission wavelength is 430 nm.The CDs exhibited excitation wavelength independence.TEM and UV-Vis absorption spectroscopy showed that the prepared CDs contains sp~2conjugated graphite lattice with an average particle size of about 5 nm.FT-IR confirmed that CDs contain rich functional groups.In addition,the polarity of the solvent increases,and the fluorescence emission peak red shifted,indicating that the surface state of the CDs have a certain influence on the fluorescence emission.(2)B-CDs,G-CDs,Y-CDs,and R-CDs with fluorescence emission at 450 nm(blue),500 nm(green),540 nm(yellow),and 600 nm(red)were prepared by simple solvothermal method under different reaction conditions.The TEM indicated CDs exhibit a circular shape and the average sizes are 2.1 nm,2.6 nm,3.0 nm and 3.1 nm respectively.Raman and XRD confirmed the graphite-like structure exists in the carbon cores,which are connected with the red-shifted emission.In addition,FTIR and XPS showed an increase in sp~2 hybrid C=C and surface oxidation C=O content.According to the above analysis,a multi-color CDs emission mechanism model was established.(3)CDs/PVA and CDs/PDMS composite films were prepared by solvent evaporation method to solve the problem of solid-state fluorescence quenching of carbon dots.The emission wavelengths of CDs based LEDs are 430 nm(blue),520nm(green),576 nm(yellow),and 610 nm(red).Besides,B-CDs,G-CDs and R-CDs are mixed in a certain ratio to achieve bright white fluorescence under the UV light.Based on this,the white LEDs have color coordinates and color temperatures of(0.2963,0.3225)and 7452K,respectively,close to the pure white color coordinates(0.33,0.33),confirming that fluorescent carbon dots can replace rare earth phosphors to achieve white LED applications..