Synthesis Of CuInS₂/ZnS Quantum Dots And Application In White Light Emitting Diodes

Compared with previous solid-state lighting,white LED?WLED?have the advantages of small volume,long life,high efficiency,energy saving,environmental protection and so on.They can become the best choice for new generation lighting sources.Nowadays,WLED are generally constructed from blue GaN LED chips with rare earth phosphors.Due to the absence of the red spectrum region,the traditional phosphor-converted WLED has a low color rendering index?usually less than 80?and a high color temperature?typically higher than 5000 K?,which limits it's application.Therefore,more and more attention has been paid to the exploration of new fluorescent materials with low cost,high efficiency and high color rendering index.Quantum dots?QDs?are a new type of semiconductor fluorescent material,which have the advantages of small particle size?avoidance of light scattering?,adjustable emission peaks,high color gamut,low-cost solution processing,and high fluorescence efficiency.In recent years,the cadmium compounds QDs were the most widely used in the application in illumination and displays.However,the high biological toxicity of these QDs limits it's application.Therefore,as the down conversion materials,it needs to develop new non-toxic QDs with high fluorescence quantum yield.CuInS₂/ZnS QDs are important semiconductor materials of I-III-VI family.They have advantages of low toxicity,small particle size,adjustable luminescence peak and wide half peak width.However,the CCT of WLED based on CuInS₂/ZnS QDs is higher than 5000 K when they have high CRI,which is not conducive to the comfort of human eyes.Based on this,the research idea of this paper is to prepare red CuInS₂/ZnS QDs with high quantum yield by simple solvothermal method.The CuInS₂/ZnS QDs were mixed with epoxy resin to prepare the fluorescent conversion film,or the QDs and commercial green light phosphors were mixed with the resin.By optimizing the proportion,the WLED devices were constructed with low CCT and high CRI.Based on the above research ideas,the following three parts were specifically carried out in this dissertation.?1?Synthesis and properties of high efficient CuInS₂/ZnS QDs via solvothermal methodCuInS₂/ZnS QDs were prepared via solvothermal method by adjusting the factors:the ratio of copper to indium,nucleation temperature,zinc source in growing shell,and oleic acid usage.The best synthesis conditions were introduced with the ratio of copper to indium is 1:2,nucleation temperature is 180°C,the amount of zinc source is 6 mmol,and the amount of oleic acid is 4 mL.Under this condition,CuInS₂/ZnS QDs with the average size of 4.8 nm and the fluorescence quantum yield up to 85.06%were obtained.The structure,morphology and spectral properties of the QDs were characterized by steady-state fluorescent spectroscopy,UV-vis absorption spectroscopy,TEM,XRD,XPS,and FTIR.It shows that the QDs have excellent fluorescence properties,which provided the materials for the preparation of high quality warm white light.?2?Preparation and application of CuInS₂/ZnS QDs fluorescent filmsThe CuInS₂/ZnS QDs with PL peak of 622 nm were mixed with epoxy resin.This process can isolate with water and oxygen in the air,which will improve the stability of the QDs.In order to make up for the deficiencies of the traditional white LED red light region,the films with different concentrations of QDs were used to adhere to commercial cool white LED chips,which can effectively improve the color temperature of cold white chips.The correlated color temperature is reduced to 3685 K from 5563 K and the color rendering index of the white LED is greatly improved to 90 from 72.The detailed performance parameters of warm white light are followed:the color coordinate CIE is?0.367,0.302?,the color rendering index CRI is 90,and the color temperature CCT is 3685 K.?3?WLED devices constructed with the hybrid of QDs and phosphorsThe CuInS₂/ZnS QDs with PL peak of 619 nm were mixed with a commercial green silicate phosphor?Ba,Sr?₂SiO₄:Eu²⁺.Then it was dispersed in the UV-curable resin for encapsulation,which was set aside for point coating on the blue GaN chip as converter.The white light can be obtained from the blue?GaN LED chip?,the green(?Ba,Sr?₂SiO₄:Eu²⁺phosphor)and the red light?CuInS₂/ZnS QDs?.The effects of the ratio of UV curable resin to fluorescent materials,the ratio of QDs to?Ba,Sr?₂SiO₄:Eu²⁺phosphor on the white LED were studied.After optimization,the best performance index of WLED devices were obtained with CIE of?0.365,0.375?,CRI of 90 and CCT of 4360 K.