<p>Carbon dots (CDs) are suitable for metal ion detection owing to their distinct optical tunability, structural controllability, and varied fluorescence response mechanisms. This research produced blue-fluorescent carbon dots (B-CDs) and red-fluorescent carbon dots (R-CDs) by a one-step microwave-assisted technique. B-CDs specifically recognized Cu²⁺ in an aqueous system, while R-CDs exhibited a distinctly selective response to Fe³⁺. Composite carbon quantum dots (B/R-CDs) with purple fluorescence were synthesized by integrating B-CDs and R-CDs, achieving superior dual-metal ion detection capabilities. Using B/R-CDs with dual fluorescence emission peaks, and by monitoring the changes in their ratio fluorescence signals, the designed ion detection system can simultaneously detect Cu²⁺ and Fe³⁺ in aqueous solutions. The detection process for the two metal ions corresponds to distinct dynamic quenching behaviors of the B/R-CDs. Specifically, Cu²⁺ and Fe³⁺ form unique coordination structures with the functional groups of the B/R-CDs, leading to different energy level arrangements. This not only enables the discriminative detection of the two metal ions by the B/R-CDs but also ensures immunity from interference by other metal ions. The synthesized dual-emissive B/R-CDs material can be prepared as a single reagent for the quantitative detection of two trace metal ions. Furthermore, test strips and test inks developed with it as the primary component enable semi-quantitative and visual detection.</p>