Eu3+ doped Cs–Bi–Cl perovskite quantum dots with diverse crystal structures for metal ion detection

The accumulation of heavy metal ions in the human body sharply affects health, drawing global attention. Consequently, there is an urgent need to develop environmentally-friendly and non-toxic metal ion fluorescent sensing probes. Herein, two fluorescent probes based on Cs–Bi–Cl perovskite quantum dots (PeQDs) with distinct structures, namely Cs3BiCl6:Eu3+ (3-1-6-E) and Cs3Bi2Cl9:Eu3+ (3-2-9-E), were successfully synthesized by using the ligand-assisted re-precipitation (LARP) method for detecting Cu2+ and Fe3+ ions in ethanol. Both PeQDs exhibit polychromatic emission, including feature emission around 505 nm and distinctive emission from Eu3+ ions in the long-wavelength region, making them suitable for ratiometric fluorescent probes. Significantly, both probes displayed excellent linear relationship with correlation coefficients of 0.998 (3-1-6-E) and 0.985 (3-2-9-E), respectively. The limit of detection (LOD) reached 6.23 μM (3-1-6-E) and 4.55 μM (3-2-9-E). Notably, the 3-2-9-E quantum dots (QDs) successfully detected Fe3+ ions in ethanol, owing to their unique photo-quenching and photo-recovery phenomena. The detection results exhibited excellent linear fitting, with a correlation coefficient of 0.996 and a low LOD of 3.6 μM. Furthermore, compared to undoped PeQDs, Eu3+ ion-doped PeQDs demonstrate strongly enhanced luminescence intensity and excellent photo-stability. This work expands the potential applications of lead-free PeQDs while simultaneously improving their luminescent properties.