Study Of Pyrolysis Prepartion,Regulation And Applicationof Carbon Dots-Based Afterglow Materials

As an emerging room temperature afterglow(RTA)material,carbon dot(CDs)based materials have gained significant attention in numerous potential applications,like optical sensing,multimodal anti-counterfeiting,biological imaging,and optoelectronic devices,due to their excellent afterglow properties,low toxicity,and facile preparation.The activation of RTA emission from CDs has made remarkable achievements in recent years,but achieving afterglow regulation of CDs material remains a significant difficulty.At present,the multicolor afterglow adjustment method of CDs materials lacks flexibility and simplicity,which is not conducive to their application under complex conditions.Furthermore,the development of tunable afterglow lifetime approaches for CDs has been rarely reported caused by a lack of systematic theoretical supervision.In light of the above-mentioned issues,this thesis systematically studies the pyrolysis preparation process of CDs-based afterglow materials through the control of pyrolysis temperature and heavy element doping,which is committed to realizing multi-color RTA of CDs-based afterglow materials and afterglow lifetime adjustment.This study will serve as a foundation for future research on the regulation of RTA properties in CDs based materials.Finally,preliminary applications of the new CDs materials were investigated.The following is the paper’s specific content:(1)The raw materials for the preparation of the CDs-based RTA materials were hydroxyethylurea(H-urea)and boric acid(BA).Three CDs-based afterglow complexes(c-CNBMs,g-CNBMs,and y-CNBMs)were synthesized by varying the pyrolysis temperature.The afterglow colors of these complexes change dynamically in the cyan,green,and yellow ranges as the pyrolysis temperature rises.Further investigation reveals that the RTA emission of the complex is responsible the n-σ* transition of the B-C/B-N bond,the π-π*transition of C=C/C=N and the n-π* transition of C=O/C=N.Besides,a gradual red shift in the RTA emission results from the production of several longer-wavelength RTA emission centers with longer wavelengths,such as C=C,C=O,and C=N,which are embedded in the solid matrix(boric oxide,B2O3)as a result of the pyrolysis temperature increasing.This work provides a feasible method for producing metal-free,long-lived,scalable CDs-based RTA materials with multicolor RTA emission.In addition,this multicolor RTA modulation method of in situ pyrolysis of carbonized carbon source precursors provides the possibility to design CDs-based RTA materials with thermal stimulus-responsive multicolor afterglow.(2)On the basis of the above pyrolysis method for preparing multi-color afterglow CDs-based afterglow materials,a series of halogen-doped CDs-based afterglow materials with tunable afterglow lifetimes ranging from 32 ms to 1.092 s are successfully prepared by adding halogen potassium salts(KX,X=F,Cl,Br,and I).Comparing the structure and photophysical properties of CDs-based afterglow materials before and after halogen doping,it is found that with the increase of the atomic number of doped halogen,the excessive carbonization of CDs gradually reduces the relative content of luminescent centers,and the luminescent center related to the amide nitrogen sufferes a more powerful static quenching effect.Eventually,the afterglow lifetimes of the resulting materials(i.e.,CNBMs-X,X=C,F,Cl,Br,and I)are gradually shortened.In orderto realize rational design,high-efficiency and long-lived RTA emission of CDs-based RTA materials.,this work provides a new strategy for regulating the afterglow emission lifetime of CDs-based RTA materials through doping of halogen elements,combined with heavy atom interaction and carbonization degree control of CDs.(3)The CDs-based afterglow materials prepared in the previous stage were used as the research object,and their potential application in optical anti-counterfeiting and information encryption were explored preliminarily.First,their applications in multicolor trademark anti-counterfeiting were investigated based on the cyan,green and yellow afterglow emission characteristics of three CDs-based afterglow complexes of c-CNBMs,g-CNBMs,and y-CNBMs.Then,a new security ink with thermal stimuli-responsive color-changing RTA was prepared using c-CNBMs as the raw materials,along with its applications in thermal stimuli-responsive optical anti-counterfeiting.Finally,thnks to the difference in afterglow lifetimes of the resulting halogen-doped composites(i.e.CNBMs-X,X =C F,Cl,Br and I),it was successfully applied to time-resolved dynamic information encryption applications.