(a) FTIR spectra where bands in general are associated to carboxyls or carbonates (from 1550 cm−1 to 1391 cm−1), to hydroxyls (from 1093 to 739 cm−1) and to ZnO (at 550 cm−1). (b) UV-Vis spectra for low, medium and high GQD concentrations, Dl, Dm and Dh, respectively, Zc(l), ZcDh:0 and (c) UV-Vis spectra for Zc-3, ZcDl-3, ZcDm-3 and ZcDh-3; insets in (b) and (c) are the Tauc plot for these samples. Note: the UV-vis spectra were measured after the PL time experiments from section 3.2 were achieved.