Note than the different overall shape of the spectra reported in Figure , differ from those reported in our previous studies. This is attributed to the fact that in our previous study a light was directly shined on the sample during measurement and the samples were not left exposed to the light of a photobox. Since the samples are here placed in the UV-vis spectrophotometer, it can be anticipated that less light is received by the samples, which leads to slower formation of the NPs in particular when ethanol is used. The samples using glycerol or [ethanol+glycerol] are less affected by this change in experimental setup. See details in SI on the influence of light environment, e.g. Figures . This observation stresses the benefit of small amount of glycerol to improve the robustness of the synthesis, for instance to light conditions. These results stress further that controlling the initial stages of the synthesis are key to achieve finer size control.