1：Experimental Design and Method Selection

The ld-CQDs were synthesized using lac dye as a precursor by a one-pot ethanol thermal method. The method avoided the use of strong acids and alkali, and reduced the numbers of required preparation steps.

2：Sample Selection and Data Sources

Lac dye was purchased from Kunming Xilaike Bio-technology CO. Ltd. All reagents were analytical pure and purchased from Aladdin Industrial Inc. Ltd. The water used was ultrapure water.

3：List of Experimental Equipment and Materials

High-pressure reactor (KOFD1-10/3 model), Transmission Electron Microscope (Tecnai G2 TF30), Scanning Electron Microscope (XL30E SEM), Fourier Transform Infrared Spectroscopy (Tenson 27), X-ray photoelectron spectrometer (PHI5000 Versaprobe-II), Elemental analyzer (Vario EL III), Thermogravimetric analyzer (STA 2500 Regulus), Particle Size Measurement (Nanotrac Wave II), Atomic Force Microscope (5500), Spectrofluorometer (FS5), UV-Vis spectrometer (Cary Series), Fluorescence spectrometer (F-4600), Laser scanning confocal microscopy (FV10i), Fluorescent inverted microscope (IX71).

4：Experimental Procedures and Operational Workflow

0.84 g of lac dye was added to 600 ml of anhydrous ethanol, stirred for 30 min, and then reacted in a high-pressure reactor at 243℃ for 24 hours. The mixture was centrifuged at 12,000 rpm for 30 min, filtered by an organic membrane of 0.45 μm, and the solid powder obtained from the filtrate after vacuum distillation.

5：Data Analysis Methods

The fluorescence intensity and quantum yield were measured. The effect of acid or alkali conditions on the fluorescence intensity of ld-CQDs was investigated. The composites of ld-CQDs/silicon dioxide were prepared and their fluorescence properties were analyzed.