Figure 6.

(a) Relative fluorescence intensity of aqueous N–CDs at λ_em = 465.5 nm in the presence of 50 µM of various individual metal ions, (b) PL emission spectra of aqueous N–CDs in the presence of different concentration of Cu²⁺ (0, 15, 30, 50, 70, 90 and 120 µM), (c) a linear correlation of I₀/I ratio and the concentration of Cu²⁺, where I₀ and I represent the fluorescence intensity in the absence and in the presence of Cu²⁺ ion, respectively and (d) UV-Vis absorption spectra of N–CDs before (red line) and after (black line) the addition of 700 μM Cu (II). Inset shows the corresponding photo images of sensing under UV lamp.