Aminophosphine-Based InP Quantum Dots for the Detection of Zn²⁺ and Cd²⁺ Ions in Water

Water is considered a pivotal molecule for colloidal III–V indium phosphide (InP) quantum dots (QDs) and significantly affects the QD crystal growth and photoluminescence (PL) stability. Herein, we demonstrate a positive aspect of water for aminophosphine-based InP QDs, that is an enhanced PL quantum yield (QY) of ∼50 times and red-shifted optical absorption (∼15 nm) after a water post-treatment of InP QDs occurring in seconds at room temperature. The phenomenon is caused by water-activated ligand exchange between the oleylammonium chloride ion pair ([OAmH+]–Cl–, X-type bound ion pair ligand) and oleylamine (OAm, L-type ligand), followed by QD surface passivation by existing Zn2+ metal ions. A similar phenomenon is also observed for intentionally added Cd2+, which increases PLQY ∼15 times together with 55 nm red-shift in the optical absorption. Taking advantage of the rapid PL response and feasible preparation process, an InP QD fluorescent probe has been demonstrated for selectively detecting Zn2+ or Cd2+ in water. The water-activated surface phenomenon for aminophosphine-based InP QDs may provide insight into the QD surface dynamics and environmental sensing applications.