Study On Synthesis And Luminescence Mechanism Of Fluorescence Carbon Nanodots With Narrow Emission Peak

Carbon nanodots(CDs)have attracted more and more attention because of their environmental friendliness,wide sources of raw materials,simple preparation methods and low biological toxicity.The synthesis methods and raw materials of carbon nanodots are also more and more diverse,but their complex core structure,abundant surface functional groups,and heterogeneous particle size may cause changes in their luminescent center and full width at half maxima(FWHM).The origin is more chaotic and seriously hinders its development and application.In this paper,the factors affecting the luminescence of carbon nanodots were studied in detail from the synthesis methods and luminescence mechanism of carbon nanodots and the regulation of conjugate size.The luminescence behavior of carbon nanodots(CDs),which was prepared by microwave-assisted heating method using phloroglucinol as a precursor,the ethanol solution of CDs is an orange solution under sunlight,and emits yellow-green fluorescence under purple light.The structural characteristics of the carbon nanodots were characterized by TEM,AFM,XPS and FT-IR.The XRD patterns indicated that the carbon nanodots were graphite oxide-structured nanoparticles,and XPS and FT-IR spectra indicated carbon nanodots.It consists of only three elements of carbon,hydrogen and oxygen,and its surface contains oxygen-containing functional groups such as epoxy(-COC-),hydroxyl(-OH)and ester(-OOCH).Moreover,the light stability of the carbon nanodots was studied by strong UV laser irradiation,and a relatively pure carbon nanodots(CDs-i)emitting light from the intrinsic core states were obtained.Based on steady-state fluorescence spectra and transient absorption spectroscopy,three luminescent centers,namely surface states,surface molecular fluorophores and carbogenic core,were found in CDs.The emission spectra showed excitation-independent peaks concentrated at 484 nm,526 nm and 550 nm.Emissions from surface molecular fluorophores and surface states exhibit weaker photostability,which undergo fluorescence quenching after prolonged exposure to UV laser light.In contrast,UV light induces deoxidation of the surface of carbon nanodots.The emission from the carbogenic core not only shows a very stable emission and a narrow FWHM value of 38 nm,but Its emission intensity is slightly enhanced after UV light irradiation.Based on this difference in photostability,we shown how the surface of CDs deoxidizes under prolonged exposure to UV light,resulting in a relatively pure,narrow intrinsic emission with an increase in fluorescence quantum efficiency from 13% to 17%.