Investigation On The Synthesis Of Graphene Quantum Dots And Their White LED Application

As a new type of carbon nanomaterials,graphene quantum dots have gained tremendous attention because of their excellent electrical conductivity and large specific surface area.It also has some characteristics of quantum dots,such as quantum confinementeffect,edge effect,small size effect and so on.The band gap of graphene is zero,when the graphene fragments are samll enough to cause excition confinement and a quantum size effect,the bandgap is opened.Luminesce on excitation,making its application in the field of optoelectronics possible.In this paper,the synthsis of dopant graphene quantum dotswere studied.Nitrogen and sulfur co-doped graphene quantum dots(S,N-GQDs)and chlorine-doped graphene quantum dots(Cl-GQDs)were synthsised.The effects of heteroatom doping(mainly nitrogen and sulfur co-doping and chlorine doping)and preparation parameters(hydrothermal temperature,hydrothermal time,and doping ratio)on the optical properties of graphene quantum dots were discussed.The obtained S,N-GQDs and Cl-GQDs were characterized by TEM,AFM,XPS,FTIR,Raman,XRD,PL,EL and other characterization methods.Under the optimal conditions,the S,N-GQDs with a uniform particle sizeof 7nm,which equals 1 to 2 layers of grapheme sheet.It shows no obvious excitation dependence,blue emission when excited at 360 nm.Quantum yield is up to 46.8%.Cl-GQDs are smaller than S,N-GQDs.The average size is only 1.5nm,while the thickness is 2 to3 layers of grapheme sheet.The wavelength of Cl-GQDs has obvious excitation dependency,there are two emission peaks,and the emission color is white light,which is uncommon.The S,N-GQDs/YAG: Ce3+/PVA films were prepared by mixing blue-emitting S,N-GQDs and yellow-emitting phosphor YAG: Ce3+ in the polyvinyl alcohol matrix.Cl-GQDs/silicone luminescent thin films were prepared by mixing chlorine-doped graphene quantum dots with silicone resin.When the dosage of YAG: Ce3 + is 0.1 g,the film emits white light under the excitation of 360 nm,the color coordinates CIE is(0.301,0.323),the transmittance is as high as 76%,which meets the requirements of optoelectronics.Cl-GQDs/silicone resin luminescent films were prepared by the combination of Cl-GQDs and silicone resin.When the dosage of Cl-GQDs was 1 ml,the luminescence intensity of the Cl-GQDs/silicone resin film was the strongest,while the CIEcoordinate is(0.28,0.33),the film transmittance is 76%.Finally,S,N-GQDs/YAG:Ce3+/PVA film and Cl-GQDs/silicone luminescent film were combined with ultraviolet chips to construct remote fluorescent white LED device.The electroluminescent properties of the device were evalued.The luminance intensity of the device increased with increasing injection current,while the CIE coordinate of the device decreased with increasing current.In addition,the stability of remote white LED devices under different operating currents is very good,satisfying the requirements of high-quality white lighting field.