Preparation And Properties Of New Type Of Composite Materials For White LED Encapsulation

With the rapid development of light-emitting diode(LED)industry,the researches of white LED are becoming more and more important.However,the commercial white LED phosphors have the drawbacks of high cost and poor performance.As a new type of carbon nanomaterials,carbon dots(CDs)are expected to replace the traditional fluorescent materials in white LED due to the excellent fluorescence property of CDs.Current researches focus on the preparation of fluorescent CDs with the properties of high fluorescence quantum yield(QY)and adjustable photoluminescence.In this dissertation,the adjustable fluorescent CDs were prepared by two methods,which are hydrothermal method and pyrolysis method under the condition that the silane coupling agent acted as the nitrogen source and citric acid acted as the carbon source.Then epoxy resin was used as solid matrix to produce fluorescent resin materials.The fluorescence properties of different CDs were investigated,and the CDs had applied to the preparation of white LED.The main contents are illustrated as follows:(1)The carbon dots@zirconia(CDs@ZrO₂)nanoparticles were prepared via one-pot hydrothermal reaction process under high temperature and pressure,which using citric acid,Zr OCl₂·8H₂O and 3-(2-aminoethyl)3-aminopropyltrimethoxysilane(AEAMPS)as the reactants.The size of the CDs@ZrO₂ was about 50 nm.The quantum yield of the CDs@ZrO₂ was up to 23.8%.The CDs@ZrO₂ nanoparticles exhibited tunable emission wavelength from 450 nm to 535 nm emission by regulating the content of citric acid in the feed.The preparation of solid epoxy resin with the adjustable fluorescence could be realized by doping CDs@ZrO₂ nanoparticles into resin.The luminescent LED prepared by CDs@ZrO₂had significant white light emission with color coordinates of(0.30,0.37)and its color rendering index(CRI)was 67.1.In summary,the solid-state nanoparticles with tunaled emission had been developed by a valuable strategy,that is,one-pot method,for white LED.(2)Silane functionalized carbon dot(Si-CD)was synthesized vis a high temperature pyrolysis method by adding citric acid into the AEAPMS.This method was easy to operate and be industrialized.The size of Si-CD was around 5 nm,and the fluorescence QY was as high as 53.0%.The emission wavelength of Si-CD aqueous solution were 435 nm under a low concentration and 540 nm under a high concentration.By doping Si-CD into epoxy resin,the composite materials had high light transmittance(>80%)and strong fluorescence emission.Meanwhile,the preparation of epoxy resin with different fluorescence emission had been realized.