Preparation Of Carbon Nanomaterials By Laser Method And Research On Their Ultraviolet Optical Properties

Compared with organic fluorescent dyes and semiconductor quantum dots, the carbon nanomaterials, as the new fluorescent materials have numerous advantages, such as stability, resist photo-bleaching, easy preparation, low toxicity, and environmentally friendly. Based on the above, carbon nanomaterials were widely used in optoelectronic devices, biomarkers, imaging and analysis detections, etc. Recently, more and more scientists are attracted to research and exploration the preparation, performance, mechanism and application of the fluorescent carbon nanomaterials due to the unique and innovative properties. However, the as-prepared fluorescent carbon dots(CDs) primarily focus on the visible region of blue, green and yellow, and the theory of fluorescent CDs remains greatly controversial. Based on the previous achievements, in this thesis, we have synthesized fluorescent carbon nanomaterials with the fluorescent properties of ultraviolet(UV) and deep ultraviolet(DUV) by a simple one-step method. In addition, we conducted further investigation and exploration on their luminescence properties, mechanism and influential factors.Firstly, the pure, soluble and stable CDs and carbon shell fluorescent nanomaterals, exhibiting UV and DUV fluorescent properties, were successfully obtained via the facile one-step laser irradiation or ablation graphite powder and metal target in liquid, respectively. Importantly, there remains no change in the emission peaks with the variable excitation wavelength.Secondly, the fluorescent CDs can be fabricated under different conditions by changing laser wavelength, liquid medium and surfactant concentration. The CDs prepared under 532 nm wavelength laser and the laser pulse of 200 mJ per pulse have the smaller size, while the CDs prepared in aqueous medium have no fluorescence. The CDs prepared in ammonia which located at the violet region of 425 nm with a red-shift. With the increasing surfactant concentration, a fluorescent blue-shift from the UV region of 370 nm to the DUV region of 290 nm was observed due to the extensively decreasing CDs size. According to the experimental analysis, we propose the fluorescence mechanism of the UV and DUV fluorescent CDs.Finally, the carbon shell structure nanoparticles were synthesized with different metal cores via laser ablation different metal targets in the organic solvents. Subsequent acid etching experiments demonstrate that there was a significant enhanced effect originated from the metal cores on carbon shell fluorescence, and the improvement degree was different along the change of metal species. For vanadium, chromium, iron and aluminum, the enhanced factors of carbon shell fluorescence are 2.58, 4.85, 3.79 and 3.85, respectively. Finally, we exhaustively investigate and put forth the surface enhancement mechanism between metal core and carbon shell fluorescence.