Stable Photoluminescence Of CNQDs Achieved By Chemical Tailoring

Fluorescent semiconductor materials,especially highly fluorescent metal-free nanomaterials have attracted much interest for comprehensive applications,such as those in quantum devices and bio-medicine field.These materials primarily include carbon dots(C-dots);carbon nanotubes,fullerene and oxidized graphene.To enhance the fluorescence of semiconductor materials and achieve tunable photoluminescence,many researches focus on modifying these materials,such as surface modification to carbon nanodots,embedding carbon nanodots into carbon nitride matrix,chemical exfoliation to graphene following with surface passivation and functionalization.Although C-dots have gained remarkable achievements in the field of photoluminescence including high quantum yield which can even reach 80%and a wide range of emission from 380 to 600 nm,it is still rewarding to search for new metal-free materials with high fluorescence efficiency.In the last decade,layered graphitic carbon nitride has attracted enormous attention as a metal-free polymeric semiconductor possessing a suitable band gap beneficial for wide application in photocatalysis field.However,many researches manifests that the photoluminescence property of carbon nitride originates from the conjugated tri-s-triazine structure of C-N sp2 clusters and relatively low quantum yield limits its application in fluorescent devices and bioimaging field.Even so,we can conclude from the theoretical and experimental analysis that amino groups combined with C-N network as edge groups can effectively increase its conjugation,leading to ? and ?*states entering sp2 band structure and probably achieving a new photoluminescence situation with high quantum yield.Herein,we research on the photoluminescence of carbon nitride on the basis of this assumption and the results are as follows:1.Through chemical tailoring for bulk graphitic carbon nitride(g-C3N4)with ethanediamine,we obtain carbon nitride quantum dots(CNQDs)solution with average particle size of 1.4 nm.According to the SAED and XRD results,original crystal structure of g-C3N4 is not broken after chemical tailoring to CNQDs.XPS and FTIR spectra exhibits that there are many amino groups on the surface of CNQDs,consistent with our experimental assumption.Further results of PL,PLE and TRPL characterization for CNQDs manifest the strong 520 nm green emission with quantum yield as high as 76%.Besides,these CNQDs show excellent structure and fluorescence stabilities under room temperature and present no fluorescent decay even under 10-h strong light irradiation.2.To apply these high quantum yield CNQDs in practice,MTT assays are performed to understand their biotoxicity.Under different concentrations of CNQD solution to incubate cells for 24 h,all the MTT results show over 80%cell viability and demonstrate the low biotoxicity and good biocompatibility of CNQDs.Further results about bioimaging show the distinct cells incubation with CNQDs under the 405 nm light excitation and reveal their potential applications in bioluminescence field.On the other hand,coating the gallium nitride with CNQDs can achieve a highly efficient transfer from blue LED to green LED.