The Design,Preparation And Performance Of Carbon Dots Afterglow Luminescent Complexes

Carbon dots,which have broad application prospects in the fields of biological imaging,photocatalysis,chemical sensing and anti-counterfeiting due to their wide source of raw materials,simple preparation methods,high photostability,adjustable emission spectrum and good biocompatibility.The abundant emission centers of carbon dots not only have excellent fluorescence properties,but also can obtain delayed fluorescence or room-temperature phosphorescence when fixed with rigid matrix,which makes the development of carbon dots based afterglow composites attract extensive attention.Carbon dots is an ideal choice to replace the traditional rare earth ion as the electron,hole capture and excited emission center,construct the composite material system,and develop a new type of long afterglow luminescent material.However,the existing carbon dots afterglow composites still have the following defects:1)The afterglow time is very short(usually less than 10 s).2)Single wavelength of UV excitation and emission.3)Easy deliquescence,poor storage stability,etc.In this paper,based on the traditional theory of long afterglow materials,by adjusting the design of the current carbon dots-matrix composite system,we explore the preparation and performance control strategies of new carbon dot-based afterglow composites.In this paper through the matrix composite carbon dots to fixed the luminescence center,preparation,on the basis of afterglow materials at room temperature,developed a simple and efficient treatment methods to realize carbon dots more luminous center model(covalent bond,hydrogen bond,the confined effect of physics)fixed together,not only realize the universality of the carbon dots at room temperature afterglow material preparation,at the same time using carbon dots and covalent bonds between composite matrix control excitation between the singlet and triplet energy band gap,for the first time the carbon dots of the mixture of near infrared rays and delayed fluorescence emission.Then,based on the theory of preparing traditional long afterglow luminescent materials,the carbon dots based long afterglow emission composites were prepared by adjusting the design of the current carbon dots based composite system.The matrix with rich defects was used as energy storage unit,and the carbon dots was used as light excitation and emission unit,respectively.The afterglow duration of carbon dots based long afterglow emission composites was up to 2 hours.The specific content has the following two parts:(1)A method of microwave-assisted heating urea was proposed to convert it in situ to cyanuric acid and compound it with CDs to realize the triplet fixation of carbon dots and the regulation of afterglow performance.Detailed characterization confirmed that a new covalent bond(C-N)was formed between o-CDs and CA.On the one hand,the formation of the covalent bond stabilizes the triplet state of o-CDs with the help of hydrogen bond and physical confining effect.On the other hand,it reduces the energy difference(?EST)between the singlet state(Si)and the triplet state(Ti)of o-CDs,effectively promoting the intersystem crossing(ISC)and reverse intersystem crossing of excitons The RISC process is an important prerequisite for obtaining TADF and RTP dual multi-mode afterglow emission.In addition,the different attenuation life of TADF and RTP makes the short-lived NIR-RTP be masked by green TADF,which is more concealment than the NIR afterglow emission of a single mode,and has great application potential in safety protection.(2)On the basis of the above work,an appropriate carbon dots(m-CDs)are selected as the excitation and emission unit to compound with cyanuric acid to construct the energy transmission system.The obtained carbon dots matrix composites emission cyan afterglow after UV excitation.The afterglow attenuation follows the law of power exponent,and the visible time is up to 2 hours.Research data shows that:mCDs and cyanuric acid form a new excited state complex,and the derived new excited state energy level is between the excited triplet energy level of m-CDs and cyanuric acid,Induces a charge separation state,realizes the storage and slow release of excited energy,and obtains long afterglow emission.In addition,we also demonstrate the application of the long-life luminescent CDs@CA material as a luminous coating for emergency sign display and the preparation of luminous pearl.The research results in this part provide a reference for realizing the long afterglow emission of carbon dots and developing a new generation of rare earth-free LPL materials.