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.