Multicolor carbon dots with concentration-tunable fluorescence and solvent-affected aggregation states for white light-emitting diodes

Multicolor emissive carbon dots(M-CDs)have tremendous potential applications in manifold fields of bioimaging,biomedicine and light-emitting devices.Until now,it is still difficult to produce fluorescence tunable CDs with high quantum yield across the entire visible spectra.In this work,a type of M-CDs with concentration-tunable fluorescence and solvent-affected aggregation states was synthesized by solvothermal treatment of citric acid(CA)and 1-(2-pyridylazo)-2-naphthol(PAN)and the formation mechanism was monitored by different reaction time and raw material ratio.The fluorescence spectra of M-CDs in organic solvents can range from 350 to 750 nm by adjusting the concentration.M-CDs possess different aggregation states in water and organic solvents,accompanied by different fluorescence emission,which is attributed to the different surface states of various component CDs in M-CDs.Moreover,the obtained products can be uniformly dispersed into polymethylmethacrylate(PMMA)solutions as well as epoxy resins to fabricate transparent CDs/PMMA films and CDs/epoxy composites,which can effectively prevent the aggregation and produce multicolor and white light-emitting diodes(WLED).In addition,the prepared WLED with Commission Internationale de L’Eclairage(CIE)of(0.29,0.31)by using M-CDs/epoxy resin as packages,demonstrating the M-CDs exhibit potential applications for light-emitting devices.