Europium-Doped Lead-Free Cs3Bi2Br9 Perovskite Quantum Dots and Ultrasensitive Cu2+ Detection

Pollution triggered by highly toxic heavy metal ions has become of worldwide critical concern; thus, it is urgent to develop an eco-friendly and nontoxic fluorescence probe for metal ions sensing. The lead-free all-inorganic perovskite quantum dots (PeQDs) could be ideal candidates but are limited by their low photoluminescence quantum yield (PLQY). In this work, we successfully fabricated Eu3+-doped lead-free Cs3Bi2Br9 PeQDs employing a modified ligand-assisted reprecipitation method. The Cs3Bi2Br9:Eu3+ PeQDs demonstrate multicolor emissions including the exciton emission of the PeQDs and the D-5(0)-F-7(J) transition for Eu3+ ion. Compared to the bare Cs3Bi2Br9 PeQDs, the Eu3+ -doped PeQDs display highly improved PLQY from 18% to similar to 42.4% and excellent water stability. Finally, nontoxic and highly efficient Cs3Bi2Br9:Eu3+ PeQDs were employed as a highly sensitive fluorescent probe for Cu2+ ion detection in water, which demonstrates a good linear range from 5 nM to 3 pM with a correlation coefficient of 0.996 and a low detection limit of 10 nM. Our work not only provides a new strategy to improve the optical performance of lead-free PeQDs but also expands their applications for metal ions sensing.