2.3. Fluorescence Quantum Yield Calculation

Fluorescence quantum yield (QY_FL) was calculated with a standard procedure, based on the comparison of the integrated luminescence intensities and absorbance values of the synthesized CDs with a reference (which depends on the emission wavelength of the sample) quinine sulfate with the following equation:

where Grad is the gradient from the plot of integrated fluorescence intensity versus absorbance and η is the refractive index [47]. Quinine sulfate was chosen as a reference fluorophore of known quantum yield (QY_FL = 0.54) [48]. Absorbance measurements were made with a UNICAM Helios Gamma, using standard quartz cells.