The schematic illustration for the selective detection of Al3+ using C-dots-R6G is presented in Scheme 2. The C-dots serve as the energy donor as well as the conjugation site for therhodaminemoiety. Thenanohybrid system showedonly blue emission at 410 nm from C-dots because unopened rhodamine could not absorb the energy from C-dots’ blue emission, leading to no FRET. Upon exposure to Al3+, the spirolactam ring in the rhodamine moiety opened, and the absorption of the open form of rhodamine overlapped the emission of C-dots, in which the rhodamine moiety could serve as the energy acceptor, finally emitting yellow. The addition of Al3+ to C-dots-R6G solution resulted in gradual decrease in the emission intensity at 410 nm with concomitant increase in the emission at 560 nm, exhibiting the blue-to-yellow emission color change. This could be clearly observed by the naked-eye under UV illumination (inset photos
in Scheme 2).