Preparation Of Multicolor Carbon Quantum Dots And Their Tunable Electroluminescent And Photoluminescent Properties

Carbon quantum dots?CQDs?are one class of quasi-zero-dimensional carbon nanoparticles with particle size less than 10 nm,which possess not only environmentally friendly characteristics of carbon materials?nontoxicity to the environment and human body?,but also excellent optical properties of semiconductor quantum dots.Hence,CQDs have broad prospects in the filed of quantum dot-based electroluminescent light emitting diodes?QLEDs?and white light emitting diodes?WLEDs?.On one hand,for QLEDs,to meet the demand for anti-quenching ability in the solid state,high fluorescence quantum yield,good film forming ability and semiconductor characteristics of CQDs emitting layers,this thesis aims at realizing controllabe synthesis of CQDs with these characteristics by selecting suitable carbon sources and surface modification additive.On the other hand,for WLEDs,to meet the demand for environment-friendly high-color rendering index?CRI?and adjustable correlated color temperature?CCT?,this thesis aims to develop a cost-effective,simple and controllable process for fabricating high performance WLEDs by selecting suitable chip and CQD phosphor.To solve the problem that efficient long wavelength?green,yellow,orange,red?emissive CQD phosphors are scarce,this thesis aims to obtain multicolor long wavelength CQDs through efficient synthesis and isolation.Through the analysis of their fluorescence properties,the luminescence mechanism of multicolor long wavelength CQDs is explored.The detailed contents and results are as follows:1.CQDs as luminescent layers for QLEDs.First,long-chain passivated fluorescent carbon quantum dots?L-CQDs?with an average diameter of 6.7 nm and a graphite structure were synthesized by a one-step solvothermal approach using phthalic acid with a benzene ring conjugated structure as the carbon source and hexadecylamine as a nitrogenous additive.The synthesized L-CQD toluene solution exhibits excitation-independent photoluminescence emission and bright blue light emission under UV excitation with a quantum yield of 13%.The L-CQDs also have anti-quenching ability in solid state and good film-forming ability.Finally,QLED were fabricated with L-CQDs as the emitting layer,which emits blue light at 4–8 V driving voltages,and the turn-on voltage is about 5.5 V and a maximum luminance reaches 5.4 cd m^-2.2.CQDs as phosphors for WLEDs.The mixture of CQDs was prepared by one-step solvothermal method using phthalic acid and o-phenylenediamine as the raw materials.The fluorescent CQDs with green,yellow and orange emission?denoted as G-,Y-,and O-CQDs,respectively?were isolated from CQD mixture by column chromatography.All the three CQDs only have one emission center.The different PL emission of G-and Y-CQDs is determined by the quantum size effect.The PL emission of O-CQDs is mainly derived from surface defect states formed by surface oxidation,with different PL emission process from G-and Y-CQDs.In addition,solid state luminous red-green-blue CQD fluorescent film is achieved through the simple mixing of red,green,and blue CQD solution without the need of curing agent and dispersants.WLEDs with high CRI?83–88?and tunable CCT?3466–7368 K?were fabricated by adjusting the volume ratio of the three CQD solutions.