Study On The Synthesis And Optical Properties Of Carbon Dots And All Inorganic Perovskite Quantum Dots

There are many kinds of quantum dots.This paper mainly studies the quantum dots of the carbon dots and the all inorganic perovskite quantum dots.Carbon dots（CDs）emerged as a new type of fluorescent nanomaterials,are applied in drug detection,drug delivery,biological imaging and gene transfer because of their high fluorescence activity,variety,biocompatibility and low toxicity.However,there are many deficiencies in carbon dots,including blue light emission,emission wavelength control and low quantum efficiency of red light carbon dots.Therefore,we study the regulation of its emission wavelength to the long wave region.The effects of reaction solvents on the emission wavelength of CDs were studied with four classical precursors（citric acid and nitrogen containing organic compounds）.Water and toluene was selected to represent the hydrohobic and hydrophilic reaction medium,respectively.The CDs in toluene solvent exist in both blue and yellow emission bands,and can be adjusted to the yellow emission band by changing the precursor.There is only one blue light emission band in the water.Further research shows that the spectral change results from the nitrogen content and functional group makes the electron transition from the carbogenic or defect state to the surface state and energy from carbogenic state or defect state to the surface state.In addition,solid states luminescent CDs-polymers were fabricated,which proved the emission characteristics of CDs continuous and controllable.This work provides a new strategy for the study of the generation of long wavelength light emitting diodes.All inorganic perovskite quantum dots（CsPbX₃）with power transmission characteristics,emission wavelength tunability,narrow emission peak（color purity;particle size distribution is uniform）with excellent luminescent properties,can realize the visible light emission spectrum and has the advantages of high luminous efficiency up to 90%,are applied to the light emitting diode（LED）,photodetector,the memristor and solar cell fields.In view of the fact that the fluorescence quantum yield（PLQY）of CsPbCl₃ quantum dots（QDs）emitted by blue violet light is very low,this problem has been studied and achieved good results.We first considerably enhanced the PLQY of the CsPbCl₃ QDs from 3.2 to 10.3%by the introduction of potassium ions（K⁺）.Then,various lanthanide elements（La,Y,Eu,Lu）were further doped into K_xCs_1-xPbCl₃ QDs.The lanthanide doped K_xCs_1-xPbCl₃ QDs still demonstrated emissions around 408 nm and the PLQY was further improved to 31%.At last,we carried out anion exchange by gradual substituting chlorine with bromine.Efficient and tuneable emissions ranging of 408-495 nm were obtained,with maximum PLQY of 90%.This work provides a new approach to improve the efficiency of blue-violet light.