The Synthesis Of High Fluorescence Quantum Efficiency Carbon Nanodots And The Study On Its Biological And Laser Applications

Nano luminescent materials have good and unique optical properties.After many years of extensive research and rapid development,new high-performance nanometer luminescent materials have been emerging,which shows important application prospects in optoelectronics and biomedicine.The research of carbon-based nanomaterials,including graphene,carbon nanotubes,and fullerenes,are the frontiers in nanoscale science and technology,which has been attracting worldwide attention.In recent years,researchers have found a new kind of carbon nano material with bright fluorescence,named as carbon nanodots(CDs).Compared with the traditional metal and semiconductor quantum dots,CDs has the advantages of simple synthesis process,low cost,good water solubility and biocompatibility,low toxicity,excellent fluorescence performance and good stability and electron transport capacity,and shows a good application prospect in biological imaging,photocatalysis,sensors and optoelectronic devices and other fields.1,In view of low fluorescence quantum efficiency(QY)of CDs,this paper proposed a better solution.The CDs with nitrogen doping and surface hydroxyl functional modification were obtained by dehydration condensation and carbonation of citric acid with amino-containing hydroxyl compounds by one-step microwavesynthesis method.The QY of the CDs can reach 99%.The characterizations of a series of CDs demonstrated that the graphite nitrogen doping and surface hydroxyl-rich modification is the reason to achieve high QY.2,In this paper,solid-state fluorescent carbon nanodots(SFCDs)with anti-aggregation caused quenching(ACQ)was developed by one-step microwave synthesis.The QY was up to 40% in solid state without any support system.SFCDs can stain the most representative fourteen bacterial species within 1 min,the dyeing effect was better than the commonly used commercial fluorescent dyes.3,In this paper,a new kind of CDs was synthesized with a concentration dependent transformation from aggregation caused quenching(ACQ)to aggregation emission(AE)(the CDs was named QECDs).The characterizations shows that the lowest excited energy level of the monodispersed QECDs matched the absorption energy level of the QECDs aggregates,so that the F?rster energy transfer occurs between the two levels,and enhanced the yellow emission of the QECDs aggregates.4,It is the first time to found that the CDs with excitation(?ex)independent characteristics are more likely to realize amplified spontaneous emission(ASE)of low thresholds than those of other CDs under laser pumping.It was found that oxygen-containing groups(C-O-C/C-O-H)was so rare in?ex-independent CDs by Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)analysis,indicating that the C-O-C/C-O-H related excited state is less in n-?* gap,so that the electrons in the excited state are centralized in ?*?n transition,making it easier to achieve population inversion.The theoretical analysis demonstrated that the radiation transition rate and the stimulated emission cross section of the ?ex-independent CDs are significantly higher than those of ?ex-dependent CDs.In addition,the ASE was first realized in all-solid CDs films with planar waveguide structure,which laid the foundation for all solid-state laser devices based on CDs.