Fabrication And Optoelectronic Properties Of All-inorganic Carbon Quantum Dots-based Light-emitting Devices

Carbon quantum dots(CDs)are a new class of nanomaterials with stable luminescence,low toxicity and good biocompatibility.Moreover,ease of functionalization of the surface and tunability of the emission wavelength has made the CDs a very promising candidate to substitute the toxic Cd and Pb-based inorganic semiconductor quantum dots.Although the synthesis and optoelectronic properties of CDs have been extensively studied at home and abroad,compositions and structures of the CDs are quite complicated owing to the various preparation methods of the CDs which leads to the unclear mechanism of CDs.Moreover,in the CDs-based light-emitting diodes(LEDs)reported at the present stage,the electroluminescence(EL)is often mixed with the composite luminescence of the organic semiconductors,making the origin of the luminescence of the CDs difficult to be clarified.Based on the research results of the CDs at present,this thesis has carried out the following research:(1)We proposed the preparation of red fluorescent CDs by a solvothermal method and a simple grinding method as well using spinach as carbon source.The luminescent properties of the red CDs were characterized by PL,PLE,absorption spectroscopy,infrared spectroscopy and TEM.The feasibility of using green plant spinach the carbon source and simple grinding method to prepare red fluorescent CDs was proved.(2)Blue fluorescent CDs were prepared by hydrothermal method using citric acid and urea as carbon sources.All-inorganic CDs-based LEDs with Ag/CDs/Si/In&Ga structure were designed for investigating the luminescence origination of the CDs.The device is designed to effectively prevent the influence of organic semiconductors on the origin of CDs.It was found that the different luminescence of the CDs are related to their carbon nuclei,the C=O and-NH2 groups,respectively.(3)We added PMMA to fabricate a PMMA/CDs composite film to study the optoelectronic properties of the device Ag/(PMMA/CDs)/Si/In&Ga.The experimental results showed that PMMA can effectively improve the flatness of the CDs and enhances the luminescence stability of the CDs.(4)We increased the urea content in the precursor and used DMF as the solvent to effectively promote the formation of-NH2 groups on the surface of the CDs during the solvothermal reaction.CDs with red fluorescent emission were achieved,as proved by the PL and EL spectra.It was confirmed that the luminescence of the CDs in the red region was related to-NH2.