Bright, Lead-Free, Colloidal Perovskite Nanoplatelets Enabled by Rare-Earth Metal Halides

Metal halide perovskite semiconductors show strong potential for next-generation optoelectronic devices including solar cells, light-emitting diodes, and lasers. This semiconductor class is distinguished by its bandgap tunability, sharp color purity, and inexpensive solution processing. Previously, by engineering the metal halide perovskite’s cation, metal, and halide composition as well as the thickness, colloidal perovskite nanoplatelets demonstrated tunable light absorption and emission – showcasing their promise for broad optoelectronic applications.¹ Additionally, two-dimensional organic-inorganic hybrid perovskite nanosheets with formula PEA₂PbX₄ (PEA = Phenethylammonium; X = Cl, Br, I) demonstrated tunable light emission and absorption across the visible spectrum.² While the use of lead or tin within colloidal perovskite nanoplatelets/nanosheets has been well studied, other metal cations could enable new non-toxic pathways for optoelectronic devices in the deep blue and violet regimes.<br/><br/>In this work, we introduce europium within metal halide perovskites to synthesize bright, lead-free, colloidal perovskite nanoplatelets. Specifically, we focus on n = 1 and n = 2 europium-based nanoplatelets governed by the formula L₂[AEuX₃]_n-1EuX₄, where L is an organic ligand, A is a cation, and X is a halide anion. The photoluminescence spectra of the europium-based perovskite nanoplatelets are centered in the deep blue to violet range (i.e., between 400 and 460 nm) – demonstrating a new route towards non-toxic high energy visible light emission. Additionally, by changing solvents, we unlock further tunable luminescence from the europium-based perovskite nanoplatelets. These results demonstrate the potential of europium-based colloidal perovskite nanoplatelets for deep blue and violet light-emitting optoelectronic devices and encourage further investigations on the rare-earth metal-based colloidal perovskite nanoplatelet material class broadly.<br/><br/><br/><b>References</b><br/>1. M. C. Weidman, M. Seitz, S. D. Stranks, W. A. Tisdale, “Highly Tunable Colloidal Perovskite Nanoplatelets through Variable Cation, Metal, and Halide Composition,” <i>ACS Nano</i> 2016, 10, 8, 7830-7839.<br/><br/>2. S. Yang, W. Niu, A.-L. Wang, Z. Fan, B. Chen, C. Tan, Q. Lu, H. Zhang, “Ultrathin Two-Dimensional Organic-Inorganic Hybrid Perovskite Nanosheets with Bright, Tunable Photoluminescence and High Stability,” <i>Angew. Chem. Int. Ed.</i> 2017, 56, 4252.