Fig. 5. (a) UV-Vis absorption and PL spectra (λ_ex = 370 nm) of Mn(ii)-NGQDs and NG; (b) PL spectra of Mn(ii)-NGQDs recorded for progressively longer excitation wavelengths from 350 to 400 nm; (c) the effect of Mn²⁺ doping concentrations on the PL spectra (λ_ex = 370 nm) of Mn(ii)-NGQDs; (d) the effect of Mn²⁺ doping concentrations on the QY of Mn(ii)-NGQDs; (e) the effect of common metal ions doping on the PL spectra of NG; (f) the effect of common metal ions doping on the QY of NG.