Boosting the Photoluminescence Quantum Yield and Stability of Lead-Free CsEuCl₃ Nanocrystals via Ni²⁺ Doping

Colloidal CsPbX₃ (X = Br, Cl, or I) perovskite nanocrystals (PNCs) have emerged as low-cost, high-performance light-emitting materials, whereas the toxicity of lead limits their applications. Europium halide perovskites offer promising alternatives to lead-based perovskites due to their narrow spectral width and high monochromaticity. Nonetheless, the photoluminescence quantum yields (PLQYs) of CsEuCl₃ PNCs have been very low (∼2%). Herein, Ni²⁺-doped CsEuCl₃ PNCs have been first reported, exhibiting bright blue emission centered at 430.6 ± 0.6 nm with a full width at half-maximum of 23.5 ± 0.3 nm and a PLQY of 19.7 ± 0.4%. To the best of our knowledge, this is the highest PLQY value reported for CsEuCl₃ PNCs so far, an order of magnitude higher than in previous work. DFT calculations demonstrate that Ni²⁺ enhances PLQY by concurrently increasing the oscillator strength and removing Eu³⁺ which hinders the photorecombination process. B-site doping offers a promising approach to enhance the performance of lanthanide-based lead-free PNCs.