Enhanced photoluminescence and stability of water-soluble ZnSe:Cu quantum dots enabled by Al3+ co-doping and multilayer ZnS shell engineering

Water-soluble Cu-doped ZnSe quantum dots are promising low-toxicity emitters, yet their applications are limited by defect-mediated nonradiative recombination, Cu-induced charge imbalance and lattice distortion, and poor long-term stability. Here, we develop a synergistic strategy combining substitutional Al 3 ⁺ co-doping with stepwise growth of a multilayer ZnS shell through sequential precursor injections. Al 3 ⁺ incorporation compensates the charge imbalance associated with Cu⁺ doping, while the multilayer ZnS shell enables progressive surface passivation and enhances carrier confinement via a graded interface. The optimized ZnSe:Cu,Al/ZnS/ZnS/ZnS quantum dots exhibit a 258% increase in photoluminescence (PL) intensity, a 10.52% enhancement in photoluminescence quantum yield (PLQY), and a 98% extension of the average lifetime (τ avg ) compared with ZnSe:Cu QDs. Notably, ZnSe:Cu,Al/ZnS/ZnS/ZnS QD powders retain 92% of their initial PL intensity after 300 days of storage under ambient conditions, demonstrating excellent long-term stability. This work provides a defect-engineering strategy for the rational design of highly luminescent and stable water-soluble ZnSe-based quantum dots.