Optical Properties Adjustment And Application Of Carbon Quantum Dots

Carbon nanomaterials have attracted the global boom of research since Walter A. Scrivens et al. isolated fluorescent carbon nanoparticles by preparative eletrophoretic method for the purification of single-walled carbon nanotubes derived from arc-discharge soot in2004. Carbon Quantum Dots (CQDs) is a kind of florescent carbon nanomaterials with qusi-speriral in shape, the size below 10 nm that possess monodisperse system.CQDs, as an emerging material, are superior to the traditional semiconductor quantum dots in their availability, excellent biocompatibility, high stability, anti-photodegradation, and low toxicity. So far, CQDs have shown various functions in catalysis, photocatalysis, photovoltaics, bioimaging, metal ion detection, and upconversion photoluminescence. Numerous preparation methods including laser ablation, electrochemical oxidation, confined combustion and chemical oxidation have been reported. However, expensive precursors, demanding reaction conditions, time-consuming purification processes and low luminescent quantum yield (<10%) are still in challenge. Similar to other nanomaterials, doping heteroatom into CQDs could create defect levels as recombination centers to alter the charge transfer and adjust device performance. Typically, N-doped carbon quantum dots have received considerable attentions due to the introduction of N level has an essential role in higher quantum yields and efficiently electron transfer. However, almost all chemical methods of doping N need further passivation or surface modification, which are complicated to remove the great deal of impurities and also not environmentally friendly. It is highly desirable to develop a facile one-pot method for the preparation of N-CQDs.In this work, we fabricated a facile and green hydrothermal approach to prepare nitrogen contained carbon quantum dots (NCQDs) with bright photoluminescence in one pot. Through the characterization and analysis, one-and two-photon fluorescence of NCQDs was discussed. The main researching contents are listed as following:1. Three kinds of CQDs were synthesized using different precursors and methods and the optical images of them can be displayed under 365nm UV lamp. The morphology and structure of the synthesized CQDs were characterized by TEM, FITR and XPS spectrum, which confirmed the success doping of nitrogen into CQDs.2. One-and two-photon fluorescence was measured to further explore the optical properties of the synthesized CQDs. The synthesized CQDs exhibited the bright green colour optical image under Ti:Sapphire Femtosecond Laser (Coherent, Libra-F-HE) with 800nm as excitation wavelength. The quadratic relationship between fluorescence intensity and excitation power suggested the truly two-photon excitation. Then we have tried to analyze and discuss the interesting phenomena:the blue one-photon fluorescence and green two-photon fluorescence.3. Finally, in view of the high quantum yield and stability, we have studied the fluorescence response of nitrogen doped CQDs to different metal ions. In our experiment, we have observed that Fe3+ions had a remarkable quenching effect on the fluorescence, while the other metal ions had little change. The mechanism were demonstrated and discussed.