Redox-Tuned Three-Color Emission in Double (Mn and Cu) Doped Zinc Sulfide Quantum Dots

The photoluminescence characteristics of colloidal Mn2+ and Cu2+ (double) doped zinc sulfide (ZnS) quantum dots (Qdots) could be drastically influenced by reactions with redox reagents. Importantly, experiments revealed Cu+ in ZnS nanocrystals rather than Cu2+, in conjunction with Mn2+, as the emitting dopant. Thus, as-synthesized aqueous Qdots emitted orange (with peaks at 460 and 592 nm) due to the host and Mn2+ dopant emissions. However, upon treatment with a reducing agent, the color changed to yellow with dual peaks positioned at 520 and 590 nm due to Cu+ and Mn2+ dopant emissions. The characteristics could be changed reversibly with appropriate redox reagents. Further, treatment with excess of an oxidizing agent led to blue emission with a single peak at 450 nm.