<![CDATA[Carbon dots (CDs) derived from citric acid have gained significant attention because of their excellent photoluminescence properties and low toxicity. However, the optimization of nitrogen doping concentration to improve fluorescence efficiency remains insufficiently explored. In this study, CDs and nitrogen-doped carbon dots (N-CDs) were synthesized hydrothermally from citric acid using ethylenediamine (EDA) at concentrations of 5%, 10%, and 15% (v/v). The influence of EDA concentration on the optical properties and fluorescence efficiency of N-CDs was systematically investigated. FTIR analysis confirmed the presence of O–H/N–H, C=O, C–O, and C–N functional groups, indicating successful nitrogen incorporation into the carbon structure. UV–Vis spectra exhibited characteristic absorption peaks corresponding to π→π* and n→π* transitions, while PL analysis revealed blue emission in the range of 445–447 nm. Nitrogen doping enhanced fluorescence intensity and quantum yield through improved surface passivation and reduced non-radiative recombination. Among the synthesized samples, N-CDs with 10% EDA showed the highest quantum yield of 43.98%, indicating the optimum doping concentration. In contrast, excessive EDA addition at 15% slightly decreased optical performance because of possible defect formation and fluorescence quenching effects.]]>
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