An “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(vi) and dopamine resulting from the inner filter effect (IFE).
A facile, economical and green one-step hydrothermal method for N-doped CDs was presented by using citric acid as carbon source and urea as nitrogen source. The fluorescence of N-doped CDs quenched dramatically from curcumin via inner filter effect.