Preparation Of Solid Fluorescent Carbon Dots And Its Application In WLED

Carbon dots(CDs)is a new type of luminescent zero-dimensional carbon nanomaterial composed of carbon core and surface groups.Since they were first reported in 2004,they have been used as candidates with the potential to replace expensive,environmentally polluting or non-renewable feedstocks in conventional fluorescent materials due to their fascinating properties of abundance of precursors,non-toxicity,economy and superior optical properties.In the fields of photoelectric display,biomedicine,energy storage and so on,CDs shows great application potential and has attracted extensive attention of scientific researchers.So far,there are still many problems that need to be solved in the study of carbon dots:1.Almost all the CDs reported have involved fluorescence from solutions.Due to the resonance energy transfer and directπ–π*interactions between CDs in the aggregate state,solid-state CQDs usually exhibit severe self-quenching.2.CDs fluorescent characteristics are greatly affected by the reaction environment(reaction temperature,reaction time,etc.)synthesis method and precursors,and moreover,the mechanism of CDs formation and luminescence mechanism is still unclear,needs further research and analyzed.3.The preparation of most carbon points is limited to laboratory conditions,and the solid carbon dots obtained by each preparation are only at milligram level.4.The formation mechanism and fluorescence mechanism of CDs are still unclear and need further analysis and research.Therefore it is very important to prepare solid-state fluorescence CDs with clarify synthesis mechanism,fluorescence mechanism and realization large-scale preparation to promote the development of carbon dots and their commercial application.Therefore,the purpose of this paper is to promote the commercial application of carbon dots,in order to solve the above problems as a starting point.The main research contents are as follows:1.Carbon dots based composite phosphors suitable for White Light Emitting Diode(WLED)were prepared by two-step method:Firstly,liquid CDs were prepared by hydrothermal method using 1,2-diaminobenzene and polyethylene glycol as precursors,ultra-pure water as solvent.Then,liquid CDs were combined with monodisperse mesoporous silica nanoparticles(MSNS)to obtain CD@MSNS composite phosphor.This work uses the currently commonly strategy of combining carbon dots with matrix materials to solve the quenching of solid fluorescence of carbon dots by increasing the distance between CDs.The phosphor obtained not only has good photostability and thermal stability,but also achieves fluorescence enhancement(PLQY increases from 36.9%of liquid to 62.5%).Through the test and characterization of CDs,MSNS particles and CD@MSNS phosphor,the principle of solid-state fluorescence and the combination of CDs and MSNS particles were analyzed.The results show that CD@MSNS is an ideal yellow phosphor for WLED.By combining the phosphor with 455nm blue light chip,successful fabricated WLED devices with color rending index(CRI),correlated color temperature(CCT),luminous efficiency and color coordinate(CIE)of 80.9,5117 K and 40.6 lm/W,(0.3003,0.3731),respectively.2.The existing preparation method was improved,and combined with the knowledge of chemical reactions,using acidic tartaric acid and alkaline diethylenetriamine as precursors,anhydrous ethanol was used as solvent,and there was no need for separation and purification.The solid fluorescent carbon point with anti-self-quenching was prepared by atmospheric air heating in one step.The universality of the experimental idea was verified.Macro quantization experiment was carried out.Under laboratory conditions,120 g CDs could be synthesis in 3 h.By analyzing the morphology,optical properties,structure and chemical composition of CDs obtained at different preparation temperatures,the formation mechanism and fluorescence mechanism of CDs were investigated.The effects of relative content of sp~2-C and sp~3-C,types and quantities of functional groups on the fluorescence of carbon points were explored.The prepared CDS was used as phosphor combining with 450 nm blue light chip to fabricated WLED device with high color stability under different current densities and close to the standard E light source.Under the current density of 20～100 m A,the color temperature is5500～5800K,the color rendering index is 82.5～83.5,and the color coordinate are(0.32～0.34,0.31～0.33).3.Based on the work of the second part,we want to further expand the practical application field of CDs.With boric acid as B source,tartaric acid as C source,diethylenetriamine as N source,anhydrous ethanol as solvent,solid fluorescent carbon dots with fluorescence almost covering the whole visible region were prepared by a two-step method.Firstly,B,N co-doped carbon dots were synthesis by using the preparation method in the second part.Then,the carbon points are heated in Muffle furnace at different temperatures to obtain CDs with different fluorescence.Under the same excitation wavelength,the series of CDs have a large fluorescence span,and the orange red fluorescent CDs have a large Stokes shift,which can well meet the application of color LED,biological imaging and other fields.Through analyzing the characterization of carbon points at different heat treatment temperatures,the effect of B element was analyzed,and the causes of fluorescence changes of carbon points were explained.