Research On The Preparation Of High-Efficiency Long-lived Afterglow Carbon Dot Based Composites And Their Applications

In recent years,carbon dots have come progressively to the attention of researchers.These novel nanoscale luminescence materials are recognized as the most promising new generation of luminescence materials due to their high chemical stability,green,non-toxic preparation process,and superior optical properties.In comparison with traditional shortlived carbon dots fluorescence materials,there has been a huge breakthrough in the field of inorganic non-metallic afterglow materials by long-lived afterglow carbon dots and their composites due to their exceptional time-resolved properties and excellent afterglow luminescence.In such a short span of a decade,the development of carbon-dot based afterglow materials has seen a leap forward,with over-and-over strategic approaches being proposed to gradually replace traditional fluorescence materials as an emerging research trend,particularly with blue and green light as typical long afterglow luminescent materials have matured in their preparation.In addition,conventional afterglow materials largely consist of toxic transition metals and heavy metal ions and the preparation process is cumbersome and complicated,which hinders their further practical application.The exploitation of facile,high-efficiency,and biocompatible green long afterglow carbon dot afterglow materials is of great research significance.In addition,carbon-dot based afterglow materials have also proven to exhibit considerable commercialization potential in the fields of OLED,data encryption,biological detection,fingerprint recognition,and textiles.The specific contents are as follows:1.Modulation and application of high-efficiency dual-mode afterglow carbon dot compositesHigh-efficiency long-lived afterglow carbon dot composite CB-Ⅰ was synthesized by a one-step hydrothermal method.It exhibits bright blue fluorescence and cyan afterglow under visible purple light excitation and achieves an ultra-high afterglow quantum yield of 35.07%.The photophysical properties of CB-Ⅰ were characterized by spectroscopy and it was discovered that CB-Ⅰ exhibits exceptional dual-mode afterglow characteristics of delayed fluorescence and room temperature phosphorescence under ambient conditions,and shows a gradual shift from delayed fluorescence-dominated emission to phosphorescence-dominated emission as the temperature decreases.Furthermore,the temperature-responsive color-tunable afterglow phenomenon was demonstrated by the different positions of the emission peaks of delayed fluorescence and room temperature phosphorescence.In addition,not only the synthesized CB-Ⅰ powder has superior optical stability,thermal stability,and air stability,but the afterglow of CB-Ⅰ also has excellent stability under the heating of 80℃ and the obvious blue afterglow can still be detected by the naked eye.To further illustrate the stable dual-mode afterglow properties of the CB-Ⅰcomposites,several sets of comparative experiments have been synthesized to support the results.Based on these experimental results,the combination of afterglow materials with excellent optical properties is applied to information encryption and anti-counterfeiting applications.This work demonstrates the rare dual-mode afterglow emission through theoretical and experimental data and provides a reliable basis for a deeper understanding of carbon dot afterglow materials.2.Heavy-atom effect facilitates the achievement of efficient long-lived room-temperature phosphorescence carbon dot compositesTo further investigate long-lived afterglow material systems,room-temperature phosphorescence MCD20 carbon dot composites were synthesized based on the same one-step hydrothermal method using gallic acid as the carbon source and boric acid as the protective matrix.The structural and optical characterization revealed that the MCD20 powder showed a single phosphorescence peak at 525 nm under 365 nm excitation,with a measured afterglow lifetime of 993.6 ms at this position and an afterglow luminescence of 9 s visible to the naked eye.In addition,the materials have stable yellow-green roomtemperature phosphorescence emission,and the measured quantum yield of phosphorescence reaches 38.62%.To achieve more efficient room-temperature phosphorescence luminescence,it is proposed to bring in heavy atoms to enhance the spin-orbit coupling values and promote the emission of phosphorescence.It is apparent that the phosphorescence quantum yields of the composites synthesized after the introduction of the atoms,chlorine,bromine,and iodine are significantly enhanced,particularly for MCD20-KBr with a phosphorescence quantum yield of 53.15%,which was an extremely high-value in the carbon-dot based afterglow material community.This work is not only an optimization and upgrade of the previous work,but also a reference for the heavy-atom effect to facilitate the construction of efficient room-temperature phosphorescence afterglow materials.3.Solid-liquid phase ultra-long lifetime room temperature phosphorescence carbon dot composites for anti-counterfeiting and bio-detection applicationsIn previous work,solid-state afterglow materials with excellent optical properties have been prepared by a one-step hydrothermal method,while room-temperature phosphorescence materials in liquid conditions are still rare.Consequently,the preparation of two carbon dot composites in both solid and liquid environments by a twostep process has enabled ultra-long-lived room-temperature phosphorescence luminescence at ambient conditions.Firstly,matrix-free L-NCDs were synthesized by a one-step hydrothermal method.Unfortunately,the L-NCDs were not characterized by morphological and optical characterization to exhibit recognizable afterglow emission at ambient conditions.Based on this,carbon dots were embedded in different matrices in a second step to achieve carbon dot composites with ultra-long green afterglow.On the one hand,the covalent bonding interactions between L-NCDs and boric acid via hightemperature hydrothermal reactions to form B-O and B-C have resulted in highly efficient solid-state long-lived afterglow materials,which emit ultra-long green afterglow of 12 s up to 1.63 s visible to the naked eye under UV irradiation.On the other hand,the continued confinement of carbon dots in silica nanospheres to form strongly covalent and hydrogen bonding interactions,enhancing the rigid structure of the cross-linked framework and protecting the emitting canter from the non-radiative deactivation process of the triplet state,which resulted in the preparation of green afterglow materials in an aqueous medium that exhibits an extremely long-lived lifetime of up to 1.30 s(nearly 7 s visible to the naked eye)at ambient temperature and atmosphere.In addition,distinctive carbon dot based room-temperature phosphorescence materials based on the preparation in solid and aqueous mediums have been successfully applied as bio-detection and anticounterfeit materials for multi-level information protection.