Professor Lan Sheng's team and collaborators of South China Normal University made an important breakthrough in the rapid and controllable preparation of fluorescent carbon quantum dots

Carbon nanomaterials, such as nano diamond, fullerene, carbon nanotubes, graphene and carbon quantum dots, have attracted extensive interest and in-depth research due to their unique properties and potential applications Carbon quantum dots were first discovered by accident in the process of purification and separation of carbon nanotubes Carbon quantum dots with size less than 10 nm are considered to be the most potential biomaterials to replace semiconductor quantum dots (containing heavy metals) due to their low cost, non-toxic and biocompatibility In addition, carbon quantum dots have a very broad application prospect in light energy conversion and photovoltaic devices At present, the traditional method of preparing carbon quantum dots, no matter from bottom to top or from top to bottom, has the common disadvantage that the preparation time is long and the controllability is poor How to realize the rapid and controllable preparation of carbon quantum dots is one of the important challenges in this field Recently, an interdisciplinary research team composed of Professor Lan Sheng from the school of information optoelectronics science and technology of South China Normal University and Professor tie Shaolong from the school of chemistry and environment has made an important breakthrough in the rapid and controllable preparation of fluorescent carbon quantum dots They skillfully use the fanuo formed in the gold nanoparticle polymer（ Fano) resonance, the temperature field with high spatial localization was obtained Combined with the ultra short time of femtosecond laser pulse, the small-scale carbon quantum dots with high efficiency white light emission were successfully prepared It is a universal physical phenomenon that the Fano resonance originates from the coherent interaction between a discrete state and a continuous state The main material for the preparation of carbon quantum dots is a film made by dispersing gold nanoparticles in polyethylene (as shown in Fig 1a, b) In the process of solvent evaporation, gold nanoparticles are easy to self assemble to form polymers (as shown in Fig 1C, d) through convection effect Each polymer can contain several or more gold nanoparticles of different sizes The surface plasmon coupling between the gold nanoparticles in the polymer can produce a Fano resonance in its extinction spectrum (as shown in Fig 1D) By aligning the wavelength of incident light with the valley or peak of Fano resonance, not only strong electric field localization but also high temperature field localization can be generated (as shown in Fig 1E, f) This highly localized temperature field is one of the necessary conditions for the generation of small-scale carbon quantum dots Fig 1 (a) schematic diagram of carbon quantum dots produced by gold nanoparticles / polyethylene films under femtosecond laser irradiation; (b) schematic diagram of white light emitted by carbon quantum dots under mercury lamp irradiation; (c) transmission electron microscope photo of gold nanoparticles used to prepare gold nanoparticles / polyethylene films, illustrated with pictures of gold nanoparticles / polyethylene films; (d) The extinction spectrum of the gold nanosphere tetramer is illustrated in the diagram of the tetramer, in which the diameter of the Central Gold nanosphere is 5 nm, the diameter of the surrounding gold nanosphere is 17 nm, and their minimum spacing is 1 Nm; the symbol of the pulse shape in the extinction spectrum represents the femtosecond laser pulse with different excitation wavelengths; (E) the electric field distribution of the gold nanosphere tetramer under different excitation wavelengths; (f) the temperature field distribution of the gold nanosphere tetramer under different excitation wavelengths (source: Advanced Materials) gold nanoparticles / polyethylene film can be irradiated by focused femtosecond laser, which can produce carbon quantum dots of different sizes Its light-emitting wavelength covers the whole visible light band, presenting efficient white light emission The production of carbon quantum dots is considered as a two-step dehydration process Gold nanoparticles are not only the heat source, but also the catalyst of polymer dehydration process The carbon quantum dots can emit bright white light under the irradiation of low power femtosecond laser, low power CW laser and mercury lamp Compared with the traditional preparation methods, the advantages of this innovative carbon dot preparation strategy mainly include: 1) carbon quantum dots can be prepared in polymer rather than solvent; 2) Carbon quantum dots can emit light without additional modification or passivation; 3) the production position of carbon quantum dots is controllable, which makes it possible to prepare carbon quantum dot arrays for sensing; 4) the preparation time of carbon quantum dots is very short, which is generated immediately under femtosecond laser irradiation; 5) the size and density of carbon quantum dots can be controlled by adjusting the laser power In a word, the rapid and controllable preparation of the carbon quantum dots can be extended to other metal / polymer systems, and its potential applications include high-density optical information storage (as shown in Figure 2), nano display, nano white light source, biochemical sensor / detection, etc Figure 2 The image o f carbon quantum dots prepared by femtosecond laser pulses with different wavelengths, (A-C) is the light field image of microscope, (d-f) is the image excited by 465 nm mercury lamp, (G-I) is the single photon confocal image excited by 488 nm laser, (J-L) is the two photon fluorescence image excited by low power femtosecond laser, (M-O) Is the similarity and contrast of the two-photon image; the length of the scale in all images is 50 microns (source: Advanced Materials) the above research results were recently published online in the international authoritative journal advanced materials (if = 21.95, DOI: 10.1002 / ADMA 201901371) South China Normal University is the first completion unit, Guangdong technology Normal University and Jinan University are the cooperation units, Professor Lan Sheng's doctoral student Zheng yunbao is the first author, and Liu Haiying is the associate researcher As the co first author, Professor Lan Sheng and Professor tie Shaolong are co correspondents This research is supported by major national R & D plan project, National Natural Science Foundation project, major basic research and cultivation project of Guangdong Province, production university research project of Guangdong Province and high-level university construction project of Guangdong Province.