IR absorption spectroscopy of carbon dots from citric acid and ethylenediamine: the relationship between their photoluminescence and structure

In this study, the change in the structure of carbon dots from ethylenediamine and citric acid during their hydrothermal synthesis was studied and the relationship between the structure of nanoparticles and the intensity of their photoluminescence was revealed. For this purpose, a series of carbon dots was synthesized with a precursor ratio of ethylenediamine : citric acid of 2 : 1 at a temperature of 140$^\circ$C and changing the synthesis time from 0.5 to 6 h. Based on the data of IR absorption spectroscopy, photoluminescence spectroscopy and optical absorption spectroscopy, three stages were identified in the synthesis: a chemical reaction at the stage of mixing precursors, the synthesis of highly efficient molecular luminophores when the synthesis time reaches 1 h, carbonization of molecules and the formation of a copolymer framework of carbon dots when the time of synthesis reaches 3 h. It has been established that the formation of a high quantum yield of photoluminescence of carbon dots occurs mainly at the second stage of synthesis.