Lead‐Free Europium Halide Perovskite Nanoplatelets

ABSTRACT Metal halide perovskites possess desirable optical, material, and electrical properties which have had substantial impact on next‐generation optoelectronics. However, given the toxicity of lead, alternative lead‐free perovskite semiconductors are needed. By fully replacing lead with rare‐earth elements, one can simultaneously address toxicity concerns while accessing alternative photophysical behavior in lead‐free systems. Here, we demonstrate the synthesis of 2D europium halide perovskite nanoplatelets governed by the formula L 2 EuX 4 where L is an organic ligand and X is a halide anion. By changing the halide composition, these nanoplatelets emit in the deep‐blue for PEA 2 EuBr 4 and violet/ultraviolet for PEA 2 EuCl 4 , with photoluminescence centered at 446 and ≈400 nm, respectively. The PEA 2 EuBr 4 nanoplatelets reach PLQYs of 11.4% and 12.8% in the solid‐ and solution‐state, while the PEA 2 EuCl 4 nanoplatelets reach PLQYs of 7.7% and 4.5%, respectively. We find that Eu 2 + readily oxidizes to Eu 3 + , particularly near the film surface, which likely contributes to reduced emission efficiency through defect‐mediated nonradiative pathways. Encapsulation improves optical stability, and further improvements may be achieved through ligand engineering, improved surface passivation, and better control over oxidation. These results show that Eu‐based nanoplatelets provide a lead‐free route toward high‐energy emissive materials, charting new pathways for optoelectronics in this energy regime.