Synthesis And Application Of Carbon Dot-based Composite Long Afterglow Materials

As an emerging member of the"carbon family",carbon dots(CDs)are usually defined as small carbon nanoparticles smaller than 10 nm.CDs possess the excellent properties of carbon nanomaterials,such as cheap and readily available raw materials,mild reaction conditions,low toxicity,Good biocompatibility,high quantum yield,chemical inertness,excellent electron transfer performance,etc,its superior performance has become a hot topic in the field of materials chemistry.Different from the traditional carbon dot materials with short-lived fluorescent luminescence properties,the long afterglow carbon dot materials with persistent luminescence properties are widely used in anti-counterfeiting technology,optoelectronic devices,bioimaging,sensing,etc.due to their high quantum efficiency and unique optoelectronic properties.It shows broad application prospects in the field of application.In this paper,CDs@Si O₂ composites,water-phase stabilized CDs@Si O₂ composites,and CDs-RhB@Si O₂ composites were synthesized by hydrothermal method,and the materials were applied in different fields such as anti-counterfeiting,sensing,and optoelectronic devices.This paper is mainly divided into the following three parts:Through the calcination method,we successfully tune the degree of carbonization of the carbon dots,and thus tune the different afterglow luminescence properties of the CDs@Si O₂ composites.The CDs@Si O₂-Raw composite was synthesized using hexamethyleneimine(HDMI)as the organic carbon source under hydrothermal conditions,and the material exhibited thermally-induced delayed fluorescence with a lifetime of 252 ms.By further calcination at 550 ^oC,the synthesized CDs@Si O₂-550exhibited room-temperature phosphorescence emission with a lifetime of 451 ms.The long-lived afterglow emission benefits from the efficient interaction of carbon dots and silica functional groups,which can stabilize the triplet state for long-lived emission.The different room temperature phosphorescence and thermally-induced delayed fluorescence emission are caused by the structural changes of carbon dots,and carbon dots with larger conjugated?-domain structure and higher degree of carbonization are obtained through the calcination process,which leads to the red emission of carbon dots.shift and larger?E_ST,resulting in room temperature phosphorescence emission.This chapter introduces a facile method to modulate the afterglow emission of carbon dot materials and demonstrates its multiple anti-counterfeiting applications.On the basis of the previous chapter,we further controlled the size and degree of hydrolysis-polymerization of CDs@Si O₂ materials by etching,dialysis,etc.,and synthesized water-phase stable CDs@Si O₂-Raw-L composites.The material exists stably for a long time in the aqueous phase and exhibits TADF luminescence with a lifetime of up to 434 ms.At the same time,its fluorescence and afterglow luminescence showed p H-responsive behavior:as the p H value changed from 10.5 to 12.0,the fluorescence intensity and afterglow intensity of CDs@Si O₂-Raw-L composite showed a linear relationship with p H value.This enables the material to be used in dual-mode p H detection.Furthermore,we introduced two luminescent materials,carbon dots and rhodamine B in situ into the hydrothermal synthesis system,and successfully synthesized a series of CDs-RhB@Si O₂ composites.By controlling the amount of rhodamine B added,the dual fluorescence emission positions of carbon dots and rhodamine B in the synthesized composites can be controlled,thereby effectively adjusting the luminescence behavior of the composites.Composite luminescent material for near-red light.The material exhibits applications in the field of solid-state white LEDs optoelectronic devices.