Synthesis And Applications Of Carbon-dots-based Composites With Luminescence

Among luminescent materials,carbon dots?CDs?are widely used in biological imaging,fluorescent probes,solar cells and photocatalysis due to their high photoluminescence quantum yields,good chemical stability,photostability,good biocompatibility,low toxicity and eco-friendly nature.Based on these advantages,CDs can be used for white light emitting diodes?WLEDs?.However,efficient CDs-based composites are difficult to achieve,which could be understood in terms of the aggregation-induced luminescence quenching of CDs in the aggregated state.To solve this problem,suitable matrices are utilized to ensure the monodispersity of CDs in the solid state.In this paper,based on the green light-emitting carbon dots and red light-emitting carbon dots,an easy and low-cost synthesis method of CDs was obtained.As well as,composites based on CDs were obtained in a convenient way.The details are as follows:1.The green emissive carbon dots@montmorillonite?g-CDs@MMT?composites were synthesized based on green emissive carbon dots and MMT clays in a convenient method by embedding g-CDs into the MMT clays.Due to the confinement of g-CDs in the layered structure of the MMT clay matrix,g-CDs are uniformly dispersed in the resulting g-CDs@MMT solid-state composites.This efficiently prevents the aggregation-induced solid-state luminescence quenching of g-CDs,and a photoluminescence quantum yield of 11%could be achieved by the g-CDs@MMT composites under a 405 nm light.Additionally,the g-CDs@MMT composites exhibit low-toxicity,excellent thermal stability,photostability,resistance to organic solvents,and a small particle size.All of these advantages enable applications in fabricating white light-emitting diodes with different color temperatures,where the g-CDs@MMT composites are applied as the color conversion layer.Furthermore,by using the g-CDs@MMT composites as a fluorescence labeling marker,the latent fingerprint detection on a variety of object surfaces could be realized.2.The green emissive carbon dots@NaCl composite?g-CDs@NaCl?were fabricated through a convenient,low cost and eco-friendly way by embedding green emissive carbon dots?g-CDs?in NaCl crystals.With the protection of NaCl host,the g-CDs@NaCl composite exhibit good photostability,significant resistance to organic solvents,and improved photoluminescence quantum yields up to 25%.White light-emitting diodes with tunable color temperatures have been realized based on the g-CDs@NaCl composite.3.Carbon dots@BaSO₄?g-CDs@BaSO₄?composites are fabricated in an easy and low-cost process by sequentially assembling Ba²⁺and SO₄^2-ions onto the surface of carbon dots through electrostatic attraction.CDs act as the nucleus to attract these reactive ions and provide the luminescent centers in the composites.This strategy is versatile for a variety of negatively charged CDs with different emission colors.The advantage of the resultant composites is that their luminescence exhibits excellent thermal and photostability,as well as remarkable resistance to strong acid/alkali and common organic solvents.These merits allow for the fabrication of CDs-based light-emitting diodes using the g-CDs@BaSO₄ composites as a color conversion layer.4.The enhanced red emissive CDs-based composites with photoluminescence quantum yields?PLQYs?of 25%were prepared by embedding red emissive CDs?PLQYs of 23%?into polyvinyl pyrrolidone?PVP?.Because of the protection of PVP,the composites could preserve strong luminescence under long-term UV excitation or being mixed with conventional packaging materials.By applying the red emissive phosphors as the color conversion layer,WLEDs with high color rendering index of92 are fabricated.