Multicolor Luminescence Of Crystal-Induced Carbon Dots And Its Application

Carbon dots(CDs),as a new type of fluorescent nano–luminescent materials,not only have the advantages of excellent optical properties,stability and biocompatibility,but also have a wide range of raw materials for their production and preparation.It has important application value in many fields,such as LED optoelectronic devices,ion detection,anti–counterfeiting patterns,cell detection,etc.Aiming at the problems of fluorescence quenching under the agglomeration of CDs,and the difficulty of realizing fluorescence tunable solid–state carbon dots.This dissertation aims to find a method for the preparation of high–efficiency multicolor emission of solid–state carbon dots and its fluorescence regulation mechanism.In the form of element doping and matrix crystallization,crystalline polychromatic solid carbon dots were obtained,the structural composition and luminescence mechanism of CDs were analyzed,and the application of CDs in the fields of latent image recognition,anti–counterfeiting and LED devices was carried out.The details are as follows:(1)Preparation and application of crystal–induced orangered fluorescent carbon dots.Using phthalic acid and thiourea as raw materials,one–step microwave pyrolysis method was used to prepare crystalline CDs(CDots/PA)with orangered luminescence and a quantum yield of 17%.Morphological and structural characterization results confirm that the crystalline structure plays a key role in the luminescence of CDots/PA,and the fluorescence spectrum of CDots/PA shows that the luminescence of the carbon dots is composed of multiple emission peaks(550–750 nm).The phthalimide–like crystal structure of dispersed CDs becomes the key to prevent their fluorescence quenching.Based on its excellent luminescence properties,the material has been applied in two aspects of LED and latent image recognition.(2)Multicolor fluorescence mechanism and application of crystal–induced carbon dots.Similarly,phthalic acid and thiourea were used as raw materials,and the crystalline CDs were prepared by the solvent(methanol)thermal method by controlling the reaction conditions.As the reaction temperature increased,the CDs exhibited five luminescent colors.Among them,the orange and yellow carbon dots have the best luminescence effects,with corresponding fluorescence quantum yields of 21.78 % and 67.75 %,respectively,while the QYs of the yellow carbon dots is the highest among the currently reported solid–state S,N co–doped carbon dots.A series of characterizations found that the temperature–affected crystal structure changes lead to changes in the morphology and surface structure of CDs,which fundamentally determine the changes in the emission color and effect of CDs.Using the luminescent properties of orange and yellow CDs,the application of white light emitting diode(WLED)devices based on these CDs as phosphors was carried out.In addition,the anti–counterfeiting application research was also carried out by using the chemical effect of the two–color carbon dots on sodium hydroxide.