Preparation And Application Of Room Temperature Phosphorescence Carbonized Polymer Dots And Their Composite Materials

In recent years,long-lived room temperature phosphorescence（RTP）materials have received widespread attention due to their large Stokes shift and long afterglow emission,and have shown great application prospects in fields such as information protection,sensing,and biological imaging.At present,RTP materials mainly include inorganic hybrids,organometallic complexes,and some pure organic compounds.At present,RTP materials mainly include inorganic hybrids,organometallic complexes,and some pure organic compounds.Among them,RTP hybrids and complexes containing precious metals have drawbacks such as high physiological toxicity,high cost,and complex preparation processes,while RTP materials with pure organic compounds face the problem of short RTP lifespan.Therefore,this undoubtedly limits their application range.As a new member of non-metallic luminescent materials,carbon polymer dots（CPDs）have attracted widespread research interest since their first report due to their excellent biocompatibility,excellent photophysical properties,simple preparation methods,and wide range of raw materials.Recently,researchers have reported on RTP materials based on CPDs,which has enabled the study of the luminescent properties of CPDs to go beyond fluorescence emission,and also indicates that CPDs have become a promising new star in the RTP material family.Generally speaking,there are two key factors in constructing CPDs-based RTP materials:firstly,it is necessary to select appropriate reaction precursors to promote spin orbit coupling,and then generate abundant triplet excitons through the intersystem crossing（ISC）process.Secondly,a reasonable structure design is needed to prevent the non-radiative deactivation of the triplet state exciton.However,due to the strong non-radiative transition behavior and the spin forbidden ISC process required to generate RTP emissions,the preparation of RTP materials based on CPDs remains very challenging.This thesis successfully prepared CPDs with both fluorescence and RTP emissions,as well as three long-lived RTP composite materials based on these CPDs,and applied them successfully in the fields of information encryption,pattern anti-counterfeiting,fingerprint imaging,and light-emitting diodes（LEDs）.The main contents of this paper are as follows:（1）Preparation and application of room temperature phosphorescence nitrogen-phosphorus co-doped carbonized polymer dotsNitrogen-phosphorus co-doped carbonized polymer dots（Arg-CPDs）were prepared by microwave assisted heating using arginine and phosphoric acid as reaction precursors.The prepared Arg-CPDs showed strong blue fluorescence emission and yellow green RTP emission.Subsequently,the morphology and chemical structure of Arg-CPDs were comprehensively characterized by transmission electron microscope,atomic force microscope,X-ray diffraction,fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,nuclear magnetic resonance spectroscopy,thermogravimetric analysis and differential scanning calorimetry.It was proved that the highly cross-linked Arg-CPDs were quasi spherical with a particle size of 7.8 nm to 14.2nm,and its mainly composed of C,N,O,and P elements with rich functional group structures on their surface.Through continuous ultraviolet irradiation,high ionic strength,p H and temperature tests,Arg-CPDs aqueous solution has excellent fluorescence stability.The photophysical properties of Arg-CPDs were comprehensively analyzed by UV visible absorption spectrum,fluorescence spectrum and phosphorescence spectrum.The results showed that the fluorescence lifetime and absolute quantum yield of Arg-CPDs aqueous solution were 7.59 ns and 13.03%,respectively.More importantly,the RTP lifetime of Arg-CPDs powder is 149 ms,and the yellow green afterglow is visible to the naked eye for about 4 s,which is still very rare for realizing RTP emission of CPDs without matrix.In addition,we also found that Arg-CPDs aqueous solution is sensitive to changes in Hg²⁺concentration,and based on this feature,linear detection was achieved in the concentration range of 100-200μM.Finally,as a stable fluorescent and phosphorescent ink,the application of Arg-CPDs in the fields of information encryption and image anti-counterfeiting were proposed and demonstrated.（2）Preparation and application of room temperature phosphorescence nitrogen-phosphorus co-doped carbonized polymer dots composite materialsOn the basis of successfully preparing Arg-CPDs,the Arg-CPDs@Si O₂,Arg-CPDs@BA and Arg-CPDs@Urea composite materials were prepared by compounding Arg-CPDs with tetraethoxysilane,boric acid,and urea,respectively.The strong interactions between Arg-CPDs and these matrices were confirmed through analysis of their structure and composition.These rigid substrates effectively weaken the non-radiative transitions caused by vibrations of the luminescent groups of Arg-CPDs through physical confinement effects,thus achieving long-lived RTP emission even in aqueous solutions.The RTP lifetime of the Arg-CPDs@Si O₂,Arg-CPDs@BA,Arg-CPDs@Urea powder and Arg-CPDs@Si O₂ aqueous dispersion are 543 ms,983 ms,570 ms and 881ms through transient spectroscopy testing,respectively,and the visible afterglow of these materials exceeds 10 s at room temperature.In addition,Arg-CPDs@BA with a lifestime close to the second level has been successfully applied to phosphorescent fingerprint imaging.Finally,based on the solid-state luminescence characteristics of the three composite materials mentioned above,three high-performance white LED devices were successfully constructed by combining them with ultraviolet LED chips.These works investigated the synthesis of novel matrix-free CPDs-based RTP materials and their composites,and comprehensively studied their chemical structure and photoluminescence performance through various characterization methods.Subsequently,a series of potential applications were constructed based on their excellent photoluminescence performance.In summary,these works have important reference significance for expanding the preparation and application of CPDs-based RTP materials.