Preparation Of High-performance Fluorescent Carbon Dots For Luminescent Devices

Carbon dots are a new carbon-based fluorescent nanomaterial discovered in the 21st century.They have good biocompatibility and chemical stability which are common to the carbon-based materials and have shown great potential in many application fields.With the widespread application of luminescent devices in human production and life,carbon dots,a green and non-toxic fluorescent material,can play a significant role in luminescent devices by replacing the conventional fluorescent materials which are hard to get or harmful to human body and environment.However,there are still some problems in this kind of material,such as the generally low quantum yield,prone to aggregation quenching and poor oil solubility,which are not conducive to the further application in luminescent devices.To this end,in accordance with these problems,we designed solutions and synthesized a series of high-performance fluorescent carbon dots.The major work is as follows:（1）In order to obtain fluorescent carbon dots with high quantum yield,through solvent-free reaction and solvothermal reaction,we used hexachlorotri-polyphosphazene to catalyze the reaction of o-phenylenediamine and m-phenylenediamine to generate blue,green,yellow and red emission carbon dots rich in phenazine and pyridine structures.Their quantum yields reached 68.1%,80.4%,64.3%and 32.8%,respectively.Monochromatic LEDs and white-light LEDs were produced by these carbon dots and both of them have excellent device performance.Monochromatic photoluminescence LEDs have high luminous efficiency and good monochromaticity.White photoluminescence LED has positive white light emission（CIE coordinates:（0.31,0.32））and a high color rendering ability（CRI=95.4）while achieving a luminous efficiency of13.6 lm W^-1,so they can be used in lighting and display fields.（2）In order to prepare high quantum yield deep-blue carbon dots,we used o-phenylenediamine and phloroglucinol as precursors for hydrothermal reaction to introduce more oxygen-containing functional groups and reduce the graphitization degree of carbon dots,and ultimately achieve high quantum yield（43.8%）and deep-blue light emission(λ_em=400 nm)of carbon dots.The photoluminescence LED prepared based on the carbon dots can achieve deep-blue light emission with a luminous efficiency of 17.3 lm W^-1（CIE coordinates:（0.17,0.11））.The carbon dots can be combined with yellow light carbon dots to prepare white light photoluminescence LED(CIE coordinates:（0.28,0.34）;luminous efficiency:20.2 lm·W^-1),meaning that they can be used for large-scale preparation of carbon dots based whitelight devices.（3）To solve the problem that CDs are prone to have aggregation-induced fluorescence quenching and poor oil solubility,we selected triphenylamine and tris（4-iodophenyl）amine as precursors and obtained carbon dots with oil solubility and solid-state fluorescence through a one-step solid-phase reaction.and the carbon dots were successfully used in the preparation of electroluminescent devices.Using the carbon dots as the host of the light-emitting layer,a monochrome light electroluminescent LED was prepared,with a maximum luminance of 227 cd·m^-2 and a maximum current efficiency of 0.47cd·A^-1.In addition,based on the good oil solubility of carbon dots,they were dispersed in the host material poly（N-vinylcarbazole）to fabricate white light electroluminescent LED with a maximum luminance of 1503 cd·m^-2 and a maximum current efficiency of 0.63 cd·A^-1.And it is at a higher level in carbon dot-based white electroluminescent LEDs.