title: Dilution-Induced Formation of Hybrid Perovskite Nanoplatelets.
abstract: Perovskite nanocrystals (NCs) are an important extension to the fascinating field of hybrid halide perovskites. Showing significantly enhanced photoluminescence (PL) efficiency and emission wavelengths tunable through halide content and size, they hold great promise for light-emitting applications. Despite the rapid advancement in this field, the physical nature and size-dependent excitonic properties have not been well investigated due to the challenges associated with their preparation. Herein we report the spontaneous formation of highly luminescent, quasi-2D organic-inorganic hybrid perovskite nanoplatelets (NPls) upon dilution of a dispersion of bulk-like NCs. The fragmentation of the large NCs is attributed to osmotic swelling induced by the added solvent. An excess of organic ligands in the solvent quickly passivates the newly formed surfaces, stabilizing the NPls in the process. The thickness of the NPls can be controlled both by the dilution level and by the ligand concentration. Such colloidal NPls and their thin films were found to be extremely stable under continuous UV light irradiation. Full tunability of the NPl emission wavelength is achieved by varying the halide ion used (bromide, iodide). Additionally, time-resolved PL measurements reveal an increasing radiative decay rate with decreasing thickness of the NPls, likely due to an increasing exciton binding energy. Similarly, measurements on iodide-containing NPls show a transformation from biexponential to monoexponential PL decay with decreasing thickness, likely due to an increasing fraction of excitonic recombination. This interesting phenomenon of change in fluorescence upon dilution is a result of the intricate nature of the perovskite material itself and is uncommon in inorganic materials. Our findings enable the synthesis of halide perovskite NCs with high quantum efficiency and good stability as well as a tuning of both their optical and morphological properties.
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Yu
authors.initials: Y
authors.lastname: Tong
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Ehrat
authors.affiliation: Chair of Applied Physics, Department of Physics, Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Department of Chemistry, Division of Molecular Imaging and Photonics, KU Leuven-University of Leuven , 3001 Leuven, Belgium.
authors.forename: Willem
authors.initials: W
authors.lastname: Vanderlinden
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Carlos
authors.initials: C
authors.lastname: Cardenas-Daw
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Jacek K
authors.initials: JK
authors.lastname: Stolarczyk
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Lakshminarayana
authors.initials: L
authors.lastname: Polavarapu
authors.affiliation: Chair for Photonics and Optoelectronics, Department of Physics and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München , Amalienstraße 54, 80799 Munich, Germany.|Nanosystems Initiative Munich (NIM) , Schellingstraße 4, 80799 Munich, Germany.
authors.forename: Alexander S
authors.identifier: 0000-0001-6168-2509
authors.initials: AS
authors.lastname: Urban
keywords: nanocrystals; nanoplatelets; osmosis; perovskite; quantum confinement; radiative and nonradiative decay