1：Experimental Design and Method Selection:

A one-step hydrothermal method was used for synthesizing N-GQDs using graphene oxide (GO) as precursor, ethylenediamine (EDA) as the nitrogen source and reducing agent, and hydrogen peroxide (H2O2) for oxidative cutting.

2：Sample Selection and Data Sources:

Precursor GO was synthesized by a modified Hummers method from graphite powder.

3：List of Experimental Equipment and Materials:

Transmission electron microscopy (TEM, JEM-2100F, JEOL Ltd., Japan), atomic force microscopy (AFM, Dimension Icon, Bruker Crop., USA), X-ray photoelectron spectroscopy (XPS, ESCALAB 250XI, Thermo Fisher Scientific Inc., USA), UV Vis spectrometer (UV-3200, Mapada Instruments Co., Ltd., China) and fluorescence spectrophotometry (Varian Cary-Eclipse, Agilent Technologies, Inc., USA). Fourier transform infrared (FTIR) spectra were collected using a Nicolet iS10 spectrometer (Thermo Fisher Scientific Inc.).

4：Experimental Procedures and Operational Workflow:

The mixture was transferred into a 50 mL para-polyphenol autoclave and heated at 200 ℃ for 3 h. After cooling to room temperature, the resulting dark-brown product was filtered through a

5：22 μm microporous membrane to remove the black gelatinous substance. The obtained dispersion was dried in an oven to obtain the powder, which was then used in subsequent characterizations. Data Analysis Methods:

The quantum yield (QY) of N-GQDs was measured using a one-point method and calculated using Rhodamine B as a reference.