Large-scale Preparation Of Solid-State Fluorescent Carbon Dots With Aggregation Induced Full-Color Emission And Their Applications

Full-color fluorescent carbon dots(CDs)have received much attention from researchers due to their numerous advantages such as easy preparation,fascinating optical properties,good biocompatibility,and low cost,and have been most explored in imaging,sensing,light-emitting devices,and security systems.The current research mainly focused on the preparation of CDs with full-color emission in the solution state,while the reports on the solid-state fluorescent(SSF)CDs are few due to the aggregation-caused quenching(ACQ)effect and the complex fluorescence mechanism.In addition,CDs usually suffer from long reaction time,complicated purification process,and low production yield,making it still a great challenge to prepare full-color solid-state fluorescent CDs on a large scale,which seriously hinders the practical application and development of CDs in the solid-state fields such as multi-color display and lighting.Recently,aggregation-induced emission(AIE)phenomena have been observed in a few pure CDs.Such CDs have self-quenching resistant solid-state emission and could be effectively purified with a simple method.These unique advantages endow this strategy with huge potential in the large-scale synthesis of CDs with intense SSF.However,there is still a lack of theoretical and experimental understanding of carbon dots with AIE phenomenon,and one-step preparation of full-color carbon dots with AIE effect has not been reported.In this work,highly efficient SSF CDs with aggregation-induced full-color emission were synthesized by heating an ethanol solution of o-phenylenediamine(oPDA)and 1,2,4,5-pyromellitic dianhydride(PMDA).The emission color of CDs can be modulated from blue to red by changing the reaction time and the precursor ratios.The photoluminescence quantum yields(PL QY)of these CDs are within 27.9-55.3%.The red emission carbon dots(R-CDs)have a QY 27.9%,which is much higher than most values reported by other works.The optical properties and structural compositions of CDs are characterized using UV-Vis spectrum,FTIR,steady-state/transient fluorescence spectroscopy,TEM,SEM,AFM,XPS,laser Raman,NMR,etc.It is found that CDs consist of graphitized core and amorphous shell,and the organic functional groups enriched on CDs surface have AIE properties.Based on their superior solid-state luminescence performance,short reaction time,easy purification process,and high production yield(85%),the kilogram-scale preparation of full-color SSF CDs was achieved for the first time.It was also found that the fluorescence redshift of CDs results from the F(?)rster resonance energy transfer(FRET),which is caused by increasing number of aromatic rings on the CDs surfaces.Based on these data analysis,the growth process and luminescence mechanism of these CDs are proposed accordingly.At last,taking advantage of their AIE effect and excellent solid-state luminescence,a series of application studies were carried out with these CDs.First,the construction of wateradded color-changing letters was tried to realize the encrypted transmission of information.Second,multicolor and white light-emitting devices were constructed,demonstrating their application potential in solid-state lighting.Finally,the R-CDs were applied to the field of fingerprint recognition,and high-definition imaging of fingerprints on a variety of materials was successfully achieved.This research provides a new strategy for massively synthesizing full-color SSF CDs,strongly promoting the development of CDs in basic research and practical applications.There are 56 figures,12 tables and 120 references in this thesis.