2.4. Calculation of Fluorescence Quantum Yield

The relative fluorescence quantum yield (QY_FL) was calculated with a standard procedure, [30,31] which is based on the comparison of the integrated luminescence intensities and absorbance values of the relevant sample (different CDs) with that of a reference fluorophore, with the following equation:

In Equation (1), Grad is the gradient from the plot of integrated fluorescence intensity versus absorbance and η is the refractive index. Quinine sulphate was chosen as a reference fluorophore of known quantum yield (QY_FL = 0.54) [32]. Fluorescence was measured with a Horiba Jovin Yvon Fluoromax-4 spectrofluorimeter. Absorbance measurements were made with a UNICAM Helios Gamma, using quartz cells.