Studies On The Fabrication,Tunable Luminescent Properties And Mechanism Of Carbon Dots And Composites

Carbon dots?CDs?,were also named carbon quantum dots or carbon nanodots.As a new type of fluorescent nanomaterials,CDs have attracted more and more attention in recent years because of their remarkable physical optical properties and wide application prospect.For instance,CDs show great potential application in the field of biosensing,bioimaging,clinical testing,diagnosis and treatment,because their high efficiency,excellent stability,green and environmental protection,low bio-toxicity and excellent bio-compatibility and so on.Also,CDs can be expected to take the place of the traditional rare earth phosphors and commercial blue chips to fabricate green,efficient and cheap LED because of their wide precursor,low cost and facile synthesis method.But there are still some shortage for CDs,the most important one is most of reported CDs are blue emitters,the long wavelength one,such as yellow,orange,and red emission CDs show low efficiency and unclear mechanism.Based on above consideration,in this thesis,we explored different approach to tune the emission wavelength of CDs,including rare earth ions doping,surface modification using organic emitting materials?polydopamine?,tuning the emission wavelength of CDs by solvation effect and control of the surface groups.In addition,the related mechanism and application has also been explored.The main contents are as follows:Firstly,a new type of Eu³⁺ doped CDs composites by one-step hydrothermal methods.The composites show unique dual photoluminescence and this characteristic has been developed to a ratio-metric pH sensors which shows good accuracy and linear relationship in the relative large range.Moreover,by co-doping with Tb³⁺,the composites can realize white light emission,and the color can be tuned by varying the proportion of Eu³⁺,which can be expected to fabricate WLED.Secondly,we prepared a new sort of CDs contained fluorescent nanoparticles?CDs-FONs?through co-polymerization of DA and CDs for the first time.The prepared CDs-FONs shows good mono-dispersity and excellent biocompatibility.By controlling the reaction time,different CDs-FONs were also prepared which showed similar structure but tunable emission.The investigation on the different CDs-FONs indicated that the tunable emission of CDs-FONs was from the energy transfer effect between CDs and porous PDA.The transfer efficiency increased with reaction time,leading to the change of emission color.At last,the CDs-FONs were applied to the cell imaging successfully and showed great potential for bio-application.Thirdly,we prepared luminescent CDs by solvothermal method based on p-phenylenediamine?PPD?in various solvents.The prepared CDs demonstrate solvents tuned emission which originate from the molecular states.Further investigation on the mechanism demonstrate that CDs show the tunable emission from green to red-orange in polar aprotic solvents because of different weak hydrogen bonding effect,and the red emission occurs only in protic solvents because of strong hydrogen bonding effect.Based on such conclusion,CDs were applied to fabricate the continuously tunable solid states luminescent CDs-polymer successfully.Lastly,citric acid and four different precursors containing nitrogen were chosen to prepare CDs by hydrothermal and solvothermal methods in the same reaction condition separately.The results indicated that only CDs with blue emission could be obtained by the hydrothermal way,but emitters with different long wavelengths were obtained through the solvothermal way.The structural analysis indicated that the blue emission originated mainly from hydrophilic surface groups concentrated in CDs prepared by hydrothermal way,and these groups largely decreased in the CDs prepared in toluene,resulting in the suppressed blue emission channels and improved long wavelength emission related to surface states.This work is expected to be used to explore more and more efficient CDs emission in long wavelength.