The Studies Of Effective Synthesis,property Regulation And Application Of Room Temperature Phosphorescent Carbon Dots

As an emerging luminescent functional material,carbon dots(CDs)exhibit great application potential in the fields of ion detection,biological imaging,information encryption because of their low preparation costs,simple synthesis methods,adjustable optical properties,good photobleaching resistance and good biocompatibility,and therefore they have received extensive attention from researchers at home and abroad.In recent years,great breakthroughs have been made in the study of the photoluminescence properties of carbon dots,and different emissive features,such as fluorescence to long-life phosphorescence and delayed fluorescence have been gradually realized.Nevertheless,the research on room temperature phosphorescence of carbon dots is still in its infancy with many problems and challenges:1)Most of the reported phosphorescence from carbon dots in the literatures depends on the protection by matrices,which limits the range of phosphorescence applications.Although there are few reports about room temperature phosphorescence of matrix-free"pure"carbon dots,the phosphorescence emission still dominated by blue and green light.The preparation of long-wavelength(yellow,red,and near-infrared)phosphorescent emitting carbon dots is difficult,which seriously hinders the further application of phosphorescent properties of carbon dots;2)At present,the phosphorescent excitation wavelength of carbon dots is still limited to ultraviolet ligh t.In practical applications,the limitation of the phototoxicity of the excitation light source is not conducive to the performance advantage of carbon dots.Therefore,there is an urgent need to prepare room-temperature phosphorescent carbon dots with characteristics such as visible light excitation,long-wavelength emission,and adjustable emission color.In view of this,the research in this thesis is focused on the regulation of"pure"carbon dot s phosphorescence excitation and emission wavelengths.Based on the previous research results to achieve"pure"carbon dot s room temperature phosphorescence,a single carbon has been achieved through the control of the carbon dot s microstructure.Multi-color room temperature phosphorescence emission(i.e.,excit ation wavelength dependent phosphorescence)regulation of dots and preparation of visible-light excitation,long-wavelength(orange-red)emission type phosphorescent carbon dots.The carbonization degree control and luminescent center regulation of microst ructure control were examined in detail.The effect mechanism of carbon dots room temperature phosphorescence,a preliminary summary of the generation process of phosphorescent carbon dot s,and the mechanism of phosphorescence emission and regulation is pr ovided,which provides a reference for the subsequent research on the regulation of carbon dot s phosphorescence performance.Finally,the preliminary application of the obtained new phosphorescent carbon dots was explored.The specific content of the paper is as follows:1.Study of the Regulation and Control of Multicolor Room Temperature Phosphorescence Property of Single Carbon DotsAccording to reports,when functional groups such as carbonyl(C=O),carboxyl(-COOH),are effectively fixed at the edge of the carbon dots,the purpose of stabilizing the triplet state can be achieved,thereby achieving phosphorescence emission.According to the guidance of this part of the theory and related mechanisms,in the synthesis part of the carbon dots of this system,the precursors that can produce such luminescent functional groups by carbonization were screened,and finally succinic acid and diethylene triamine were used as the carbon precursor raw materials,Through hydrothermal carbonization,a new room temperature phosphorescent carbon dot s with different emission wavelength(multicolor)was successfully synthesized.The phosphorescence lifetime of this carbon dots is up to 0.86 s(the naked-eye lifetime can be up to 5?6 s),and with the change o f excitation wavelength,the emission wavelength of phosphorescence shifts from 500 nm(green)to 585 nm(yellow).In addition to the long-wavelength(580 nm)phosphorescence emission,the preparation of self-protected multicolor room temperature phosphorescent carbon dots was also realized for the first time.In-depth studies have found that when the carbonization degree of carbon dots is adjusted,the micro-morphology of carbon dots and the content of luminescent functional groups will change regularly.I n addition,the optical properties of carbon dots will also change accordingly.Through the analysis and summary of the relevant data and the subsequent confirmatory experiments,it is inferred that under the crosslinking of the carbon chain around the carbon dots,the C=O/C=N group can form various conjugates in the hydrothermal process,and can act as an emission center with different energy gaps,and the C=O/C=N group can improve spin-orbit coupling and promote the ISC process,thereby effectively filling triplet excitons.The entangled carbon chain can also serve as a matrix for fixing the emission center,thereby forming stable triplet substances by forming hydrogen bonds and thereby fixing other groups on the carbon chain(for example,-OH/-NH₂).As the excitation wavelength changes,different emission centers will dominate the RTP process and therefore display different colors.Based on the unique optical properties of this carbon dot s,the anti-counterfeiting ink made with this carbon dots as a raw material can be applied to new anti-counterfeiting fields such as photo-stimulating information encryption.2.Study of the adjustment of phosphor excitation and emission wavelength of carbon dotsIn order to further expand the application scope of phosphor escent carbon dots and break the shackles of existing phosphorescent materials.In this system,environmentally friendly amino acids were used as precursors.After preliminary screening,aspartic acid was selected as the precursor,and microwave method was used as the carbonization method.During the carbonization process,aspartic acid carbonized itself under the action of ammonia,forming a carbon dots with a phosphorescence lifetime of 240 ms.Under the excitation of visible light(420 nm LED),the carbo n dots emits orange-red phosphorescence(585 nm).As the excitation wavelength increases,the longest emission wavelength can reach 650 nm.Under the premise of self-protection,the control of the excitation wavelength and emission wavelength of this carbon dots has been successfully achieved.Through compared the three different state materials of the precursor aspartic acid,moderately carbonized carbon dots,and deeply carbonized carbon dots,inferring that during the carbonization process,aspartic acid formed a cross-linked structure.The different luminescence centers such as C=N and C=O on the surface are fixed to make it have excellent fluorescence and phosphorescence properties.Through the regulation of the luminescent center,it can be found that a large number of C=N functional groups can enhance the characteristics of the carbon dots excitation wavelength dependent phosphorescence.The unique optical properties of the carbon dot s make it free from problems such as phototoxicity.Therefore,its application of information encryption and anti-counterfeiting will be more valuable.