Preparation And Luminescence Properties Of Carbon Nanoparticles And Associated Composite Nanostructures

Compared with the conventional group Ⅱ-Ⅵ compound semiconductor quantum dots(QDs),the carbon nanoparticles do not contain heavy-metal atoms,thus they are more biocompatible and do not pollute the environment;their source materials are abundant on earth and thus they are inexpensive.Compared with the silicon QDs that belong to the same group,the carbon nanoparticles can be synthesized by using a variety of simple methods.The luminescence properties of the carbon nanoparticles are special and complex;as a result,these nanoparticles have exhibited wide application potential in the areas of biomedicine and optoelectronics.In this thesis we report the synthesis of the C8-structured carbon QDs by using carbonization of sucrose with assistance of oleic acid.Their photoluminescence(PL)properties can be altered through surface functionalization.The PL mechanisms are investigated.We have designed and fabricated light-emitting devices(LEDs)based on C8 QDs.We study their carrier transport and recombination properties.We fabricate the Fe3O4@C core-shell magnetic nanoparticles by using the hydrothermal method.The selected-area electron diffraction and the X-ray diffraction confirm the C8 structure of the synthesized carbon nanoparticles.These carbon nanoparticles exhibit PL spanning a wide spectral region(390-640 nm).The PL spectra comprise two emission peaks centered at 430 and 520 nm.It is found that the green emission peak vanishes after addition of NaOH into the Cs QD solution followed by irradiation with UV light for 8 h.The comparative study of the surface structures and light absorption properties of the pristine QDs and the treated QDs reveals that the green emission originates from the ester group-related surface defect.The inorganic/organic hybrid LEDs based on C8 QDs exhibit unique electroluminescence properties.The color of the electroluminescence of the LED changes from blue to green and red when the bias changes.Through analysis of the structure,energy-level distribution,and J-V curve of the device in conjunction with analysis of the PL properties of the carrier-transport layers and the QD layer,we reveal the underlying physical mechanism behind the electroluminescence of the devices.We find that when the bias varies,the carrier potential barrier at the interface of the device changes,which leads to variation of the mechanism of the carrier transport,and the recombination spatial region of the electrons and holes in the device also changes:as the bias increases,this recombination region shifts from the electron transport layer to the QD layer,and such a transition results in change of the emission color from blue to green and red.We fabricate the Fe3O4 nanoparticles with diameters of 7-20 nm by using the co-precipitation method.These Fe3O4 nanoparticles serve as seeds for further synthesis of the Fe3O4@C core-shell magnetic nanoparticles by using the hydrothermal method.Sucrose is used as the carbon source material.The transmission electron microscopy,the X-ray diffraction,and the Raman spectroscopy together confirm that the synthesized particles are core-shell-structured magnetic nanoparticles.There exist mainly carbon-and oxygen-associated chemical groups on the surface of the composite nanoparticle.The encapsulation of the carbon shell improves the stability of the Fe3O4 nanoparticles.The good conductivity of the carbon shell may help to improve the capacity and stability of circulation of the Li battery equipped with anode of the Fe3O4 nanoparticles.