Fig. 4.

(a) Plot of relative fluorescence intensity of FWCDs solution in different metal solutions. (b) Fluorescence decay curves of FWCDs in the absence and presence of Fe³⁺ under excitation of 342 nm. Fe50, Fe100 and Fe250 refer lifetime decay of FWCDs in the different Fe³⁺ concentrations of 50, 100 and 250 μM, respectively. (c) UV–vis absorption spectra of Fe³⁺ and FWCDs, and photoluminescence excitation/emission curves of FWCD.