Preparation,Luminescence Mechanism And Application Of High Efficiency Solid-State Carbon Dots With Multicolor Emission

As a new member of the carbon family,carbon dots(CDs)not only inherit the advantages of good biocompatibility and abundant raw material sources from traditional carbon materials,but also exhibit outstanding luminescence characteristics,such as,tunable emissive wavelength and light bleaching resistance.They show great application prospects in many fields.Therefore,CDs have been paid wide concern and given deep explanation since firstly found in 2004.In order to solve problems including serious self-quenching of aggregated CDs,complicated process for resisting fluorescence quenching and lack of tunable full color solid-state fluorescence,this dissertation aims at exploring simple reaction system and post-treatment means to construct solid CDs with tunable solid-state luminescent emission by screening reaction sources,synthesis process and dispersion matrix.On the basis of heteroatomic doping strategy,small molecule precursors with conjugated structure including p-phenylenediamine and phloroglucinol were selected as carbon sources,and ethylenediamine,urea and boric acid as dopants.CDs with efficient multicolor luminescence in solid state were obtained by adopting facile one-step hydrothermal method and microwave method along with optimizing the preparation process.The relationship between structure,surface composition and spatial arrangement of CDs and performance of agglomerated luminescence was investigated.Finally,their application in multicolor and white LED was realized.The main work includes following four parts:(1)Preparation and solid-state fluorescence mechanism of high efficiency solid-state orange emissive carbon dots/silica.To overcome self-quenching of carbon dots(CDs)in solid state and provide a universal strategy for efficient luminescence of CDs in solid state,this work reports a novel method of physical embedding of solid-state CDs into a silica matrix.CD/silica composites were prepared through injecting N-(3-(trimethoxysilyl)propyl)ethylenediamine into a CD aqueous solution.CD/silica film and powder exhibited a high quantum yield of 38.2%and 41.7%.A mechanism of photoluminscence(PL)quenching in solid-state CDs and PL resuming in CD/silica composites was proposed.These CD/silica composites possess excellent film-forming ability,thermostability and ultraviolet(UV)stability.Finally,light emitting diode(LED)was constructed by combining CD/silica and ultraviolet(UV)chip.(2)One-step synthesis and dual-emission luminescence mechanism of high efficiency solid-state yellow/orange emissive carbon dots.To directly obtain long-wavelength emissive CDs with high solid-state QY,CDs were synthesized by one-step microwave method with phloroglucinol as carbon source,ethanediamine as nitrogen dopant and boric acid as boron dopant in water.CDs exhibit high solid-state QY and dual emission.The orange emissive nitrogen and boron co-doping CDs exhibit a solid-state QY of 31.7%and dual emission at 484 and 585 nm.The yellow emissive nitrogen and boron co-doping CDs exhibit a solid-state QY of 39.0%and dual emissions at 484and 565 nm.Nitrogen and boron co-doping can synerg istically improve content of graphitic N and B–O,which is beneficial to high solid-state QY.In addition,dual emission of CDs come from carbon core and surface defect.Finally,LED was constructed by combining CDs and UV chip.(3)One-step synthesis and red emission mechanism of solid-state red emissive carbon dots.To further broaden emissive wavelength of CD powder and to obtain red-emissive CDs,dimethyl formamide/water mixtures are selected as solvents,phloroglucinol,ethanediamine and boric acid as raw materials.CD powder exhibits red emission at 623 nm with a solid-state QY of2.6%.The I_G/I_Dof CDs is up to 7.95,indicating high graphitization,which is responsible to red emission of CDs.The emission of CD powder possesses remarkable red-shift of 198 nm with respect to that of dilute solution(0.05mg/m L).CDs exhibit aggregation-induced emission red shift.Finally,on basis of unique concentration-dependent PL of CDs,multicolor LED was constructed by using different concentrations of CD solution as the fluorescence film combining with the UV chip.(4)One-step synthesis and luminescence mechanism of solid-state full-color tunable carbon dots.To obtain tunable full-color solid-state CDs and further to investigate their multicolor fluorescence mechanism,CDs were prepared using phloroglucinol and urea by one-step microwave method.Tunable full-color solid-state PL of CDs was realized by regulating reactant ratio and microwave power.The emission of CDs gradually shifts from 445 to643 nm,and QY of five typical CDs with blue(B),green(G),yellow(Y),orange(O)and red(R)emission reaches up to 48.2%,26.0%,18.5%,13.7%and 5.7%,respectively.It is the first time to realize full-color solid-state CDs without additional disperse matrices.G-,Y-,O-,R-CDs exhibit aggregation-induced emission red shift.While,B-CDs show unique crystallization-induced luminescence enhancement.Finally,CDs are utilized as phosphors combing with UV chip to fabricate and multicolor LED and white LED with with tunable correlated color temperature.On the basis of above study,it is found that the spatial arrangement and surface functional groups of CDs impose great influence on their aggregated fluorescence.To be specific,efficient steric effect is necessary for solid-state emission,and increased graphitic N and B–O is beneficial to solid-state emission.Further,increase in particle size and graphitization of CDs caused by high carbonization can collaboratively promote the redshift of solid-state CDs.Finally,the fabrication of LED was realized on the basis of multicolor solid-state CDs.