The Preparation Of Tunable Fluorescent Carbon Dots And Their Application In White LED

Due to the excellent quality in terms of luminescence,chemical stability,low toxicity,biocompatibility,carbon dots(CDs)have been attracting intensively attention over the past decade.The common as-synthesized CDs solution present blue to green luminescent,the highest reported that PL quantum yields(QY)of blue and green CDs solution are more than 80%,50% respectively.In spite of a handful reports have reached red emission,the achievement of high QY long-wavelength CDs(LCDs)solution is still a great challenge compared with short-wavelength CDs.Whether CDs can be designed like quantum dots,so as to tune full color photoluminescence(PL),which is a crucial requirement successfully executing CDs in the most application.In this paper,a series of tunable CDs were synthesized by hot-injecting and solvothermal methods.In addition,solid-state composites materials were fabricated to prevent the aggregation-induced solid-state fluorescence quenching.Then a series of characterization methods were used to investigate the microstructure and luminescence properties of these CDs.And finally,white LED devices were fabricated by matching with commercial GaN blue chips to discuss the application value of CDs.According to the above research points,the research content of this paper is divided into the following sections:1.LCDs were synthesized by hot-inject methods.A facile approach is proposed for fabrication of Ag NPs/LCDs(Ag-LCDs)hybrids,wherein Ag NPs work as a fluorescent reinforcer to enhance PL intensity of LCDs.The largest enhancement was acquired through adjusting the volume ration between Ag NPs and LCDs.In this process,PL decay is considered as an important and simple characterization to speculate the metal enhanced fluorescence(MEF)mechanism.On the basis of result of small reduction in lifetime,we proposed that the mechanism may be predominantly derived from the localized effectric field effect and partly from the intrinsic radiative decay rate.Finally,WLED was fabricated by these films with controllable thicknesses.2.Full-color light-emitting CDs were synthesized by simple solvothermal methods,where anhydrous citric acid worked as C source,urea acted as N source,DMF worked as solvent.Although all samples showed uniform distribution of particles size and similar graphite structure,the surface chemical composition gradually varied among CDs,especially the oxygen contents and nitrogen contents.Detailed material characterization has revealed that this tunable emission is resulted from the changes of the chemical composition.It is believed that the surface oxidation become more severe at high temperature,resulting in the formation of higher oxygen and nitrogen,which are responsible for the long-wavelength emission.Meanwhile,flexible solid-state materials were successfully created by combination of organosilane(OSi)and CDs,which can be used to prevent the aggregation-induced solid-state fluorescence quenching.Finally,CDs were stacked on the phosphor in-glass(PiG)via tape-casting technology.WLEDs were constructed by these materials and GaN chips.3.A series of N-doped CDs with tunable luminescence were prepared by solvothermal method using o-phenylenediamine,p-phenylenediamine as carbon source and DMF as solvent respectively.The morphology and surface functional groups were studied by various analytical methods.The effects of carbon source concentration,solvent polarity and pH on the fluorescence peak and intensity of CDs were also studied.Finally,PVB is selected as the solid matrix,and a WLED is prepared by screen-printing the red carbon dot film on the glass-ceramic surface by screen printing.