Fabrication And Luminescence Mechanism Of Red Light Carbon Dots From Amaranth

Carbon dots(CDs)will be widely used in many fields such as nanomedicine,biological imaging,biosensors,photoelectric devices and photocatalysis due to the advantages of excellent fluorescence characteristics,optical stability,biocompatibility and water solubility.At present,the preparation and functional methods of CDs have been made a lot of achievements.The synthesis of bright blue and green fluorescent CDs has many methods,is also very easy to make,but the red CDs(R-CDs)can only emit weak fluorescence,preparating also relatively difficult,especially the fabrication of the near infrared up-conversion fluorescence CDs,so far still faces a bigger challenge.In order to solve this problem,and from the perspective of environmental protection,this thesis choose the amaranth(commonly known as millet food)as carbon source,by adopting the combination of hydrotherm and pyrolysis methods,through high temperature dehydration,carbide,synthetic CDs,then using different types,different concentrations of chemical modifier on the modification and functionalization,making them become a water soluble and dispersancy good R-CDs.The method made of R-CDs is simple,low cost of raw materials,zero pollution in the preparation process,no harm to human body and the environment,and the R-CDs produced have high added value and are widely used.Some innovative research results of this thesis are as follows:1.To cheaply amaranth as carbon source buyed from the market,by using the combined method of hydrothermal reaction and pyrolysis,dehydrating and carbonizing organic matter of amaranth to form CDs and then,using different types of different concentrations of modifier on the function,make it be near infrared fluorescent CDs with water-soluble and the up-conversion function.It has found that the impurity level of CDs plays a key role for the up-convrsion red-light emission,and modifier types and concentrations have a great influence for fluorescence wavelength and intensity of CDs.2.CDs modified using ethanol solution,it was found from the fluorescence test that CDs has the performance of red fluorescence emission with the narrow band.Under the excitation of 320-420 nm or 740-900 nm light irradiation,CDs can emit red fluorescence,the fluorescence peak is located at 672 nm,half peak width(FWHM)of 25 nm.XPS test results show that the CDs dispersed in ethanol solution include N impurity,the N atom content is 7.14%.There are a large number of hydrophilic oxygen-containing groups at the surface and edge of CDs,such as-O-C=O and –OH,it makes CDs be superior water-soluble.3.CDs modified using 10 mg/ml NaOH solution,it was found from the fluorescence test that CDs have the same excellent performance of red fluorescence emission,and can emit red fluorescence under 320-420 nm or 740-900 nm excitation light,the fluorescence peak is located at 662 nm,half peak width(FWHM)of 25 nm.TEM observation show that the average size of CDs is 4.59 nm,particle size distribution between 2-9 nm,CDs dispersed evenly in the solution,high crystallinity and crystal lattice the stripe is clear,spacing of about 0.218 nm,corresponding to the(100)plane of graphite.4.CDs modified with NaOH solutions of different concentrations(10 mg/ml,15 mg/ml,20 mg/ml,25 mg/ml,30 mg/ml)had different absorption peaks.However,it is worth noting that when the concentration of NaOH solution modified CDs varied between 10 mg/ml-30 mg/ml,there were obvious ultraviolet characteristic absorption peaks around 275 nm that did not vary with the concentration of the modifier.The absorption peaks were caused by the ?-?* transition of the C=C double bond.In addition,when the concentration of NaOH solution changes,it is still accompanied by its unique weak absorption characteristics around 315 nm,418 nm,440 nm and 660 nm,among which the absorption at 315 nm is caused by the n-?* transition of the C=O double bond.Other absorption peaks are closely related to impurities in CDs,which cause red fluorescence emission in CDs.5.CDs preparated from the amaranth emit the fluorescence at the same peak position of near 672 nm under both 740-900 nm and the 320-420 nm exciting light.Since their Stokes displacement is larger,the probability CDs to absorb more phonon at the same time is small,so estimate the up-conversion fluorescence mechanism of CDs may be two-photon /multiphoton process.6.In this thesis,CDs preparated from amaranth all have up-convrsion fluorescence,the fluorescence emission peak near 672 nm,belongs to the red light/near-infrared region,its up-convrsion mechanism may be induced by the interaction among electrons at the surface state of CDs with phonons and photons.The up-convrsion mechanism are great potential application in the fields of cell remarking and biological imaging,especially for in vivo imaging and treatment of tumor,has obvious advantages.