Study On The Luminescence Performance Of Room Temperature Phosphorescent Carbon Dots

Room temperature phosphorescence(RTP),as an significant photoluminescence phenomenon,has attracted widespread attention due to its long luminescence lifetime,large stokes shift and good environmental stability.Traditional RTP materials include organic metal complexes and pure organic compounds,which have problems such as complex preparation,poor stability,or high cytotoxicity.Carbon dots(CDs),as a new type of carbon based nanoluminescent material,has attracted widespread attention due to their excellent photophysical properties,good biocompatibility,low cost,and easy preparation,making them an ideal room temperature phosphorescent material.However,because the spin forbidden transition usually leads to the low cross efficiency between the systems in which the electron transitions from the lowest excited singlet state(S1)to the lowest excited triplet state state(T1),and the triplet state exciton is unstable,which is easy to inactivate through non-radiative transitions such as vibration and rotation,resulting in short luminescence lifetime of CDs,low phosphorescence quantum yield,and usually phosphorescence performance in low temperature or inert gas.In addition,the vast majority of reported RTP CDs have a single color and only emit phosphorescence in the short wavelength region of blue or green,which limits the further application of RTP CDs.This article addresses the above issues by combining heteroatom doping,matrix assisted methods,and strategies to adjust excitation wavelength,matrix type,and energy transfer to achieve the regulation of the phosphorescence characteristics of RTP CDs.The major research content is as follows:(1)Aiming at the problems of short phosphorescence life and low quantum yield of RTP CDs,we introduced heteroatoms to promote the cross between S1 and T1 systems.At the same time,we introduced the rigid matrix magnesium phosphate to stabilize the T1 exciton and inhibit the non-radiative transition to design N,O-CDs@IP composite.The successful preparation of the material was demonstrated through basic characterization such as TEM,XRD,FT-IR,and XPS,and the optical properties and applications in fingerprint detection and multi-level anti-counterfeiting were investigated.The results indicate that N,O-CDs@IP composite has ultra-long lifetime and ultra-high PhQY.Meanwhile,due to the dense band structure of graphene in N,O-CDs,N,O-CDs@IP composite exhibit wavelength dependent excitation characteristics,as the excitation wavelength changes from 254 nm to 365 nm,N,O-CDs@IP composite exhibits different RTP colors,transitioning from blue(482 nm)to green(518 nm),phosphorescence lifetime from 2.04 s to 1.15 s,and PhQY from 24.70%to 19.88%.The wavelength dependent properties of phosphorescence in N,O-CDs@IP composite have achieved multicolor regulation of RTP CDs,and their preliminary applications in fingerprint recognition and advanced information encryption have shown good application prospects.(2)RTP lifetime is one of the important parameters of RTP CDs.This chapter uses PVA and B2O3 matrices to regulate the phosphorescence lifetime of CDs,and constructs a CD@PVA and CD@B2O3 composites.The successful preparation of the material was demonstrated through basic characterization such as TEM,XRD,FT-IR,and XPS.Subsequently,the optical properties of the material and the interaction mechanism between CDs and the matrix were investigated,and its application in multi-level anti-counterfeiting was explored.The results indicate that the modulation of phosphorescence lifetime from 0.50 s to 1.45 s is achieved due to the different mechanisms of interaction between CDs,PVA,and B2O3.At the same time,due to the two different luminescence mechanisms of CDs embedded in the rigid matrix B2O3,they exhibit blue RTP(440 nm)and green thermal activated delayed fluorescence(TADF)(550 nm),achieving the regulation of afterglow color and providing new ideas for the phosphorescence lifetime and light color control of RTP CDs.(3)Energy resonance transfer is an effective means of achieving light color regulation.This chapter utilizes the phosphorescence emission spectrum of CDs@SiO2 overlaps with the absorption spectrum of InP/ZnSe/ZnS,and the CDs@SiO2-InP/ZnSe/ZnS composite.The successful preparation of the material was demonstrated through basic characterization such as TEM,XRD,FT-IR,and XPS for CDs@SiO2 and InP/ZnSe/ZnS.And examined the optical performance of CDs@SiO2,InP/ZnSe/ZnS and CDs@SiO2-InP/ZnSe/ZnS shows that the control of RTP CDs phosphorescence color from green(525 nm)to orange red(610 nm)has been achieved through energy resonance transfer strategy,providing a way and strategy for the regulation of RTP CDs afterglow color in the red or even near-infrared region.