Nitrogen-doped carbon dots (N-CDs) were synthesized utilizing tryptophan and o-phenylenediamine as precursors, with ethanol and water serving as solvents, via a solvothermal method. The effects of the molar ratio of tryptophan to o-phenylenediamine (n(tryptophan)：n(o-phenylenediamine)) and the reaction duration on the synthesis of N-CDs were assessed based on the quantum yield measurements of the N-CDs. The morphology, structural composition, and thermal stability of the N-CDs were characterized and evaluated employing FTIR, XRD, TEM, XPS, and TGA techniques. The optical characteristics of N-CDs were investigated through fluorescence spectroscopy, quantum yield quantification, and fluorescence lifetime assessments. The outcomes demonstrated that the N-CDs synthesized with a n(tryptophan)：n(o-phenylenediamine) ratio of 1.5:1 and a reaction duration of 6 hours exhibited the optimal quantum yield (13.95%). The N-CDs possessed a spherical structure with an average diameter of 3.65 nm and a surface enriched in polar functional groups, including amino, hydroxyl, carboxyl, and carbonyl groups. The peak excitation and emission wavelengths of the N-CDs were 535 nm and 601 nm, respectively, with an absolute quantum yield of 21.39% at 535 nm. The solution of N-CDs displayed blue fluorescence under acidic conditions and a pink hue without fluorescence under alkaline conditions, indicating pH-sensitive color and fluorescence changes.