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Nearly Monodisperse Insulator Cs4PbX6 (X = Cl, Br, I) Nanocrystals, Their Mixed Halide Compositions, and Their Transformation into CsPbX3 Nanocrystals
journal contributionposted on 2017-02-14, 00:00 authored by Quinten A. Akkerman, Sungwook Park, Eros Radicchi, Francesca Nunzi, Edoardo Mosconi, Filippo De Angelis, Rosaria Brescia, Prachi Rastogi, Mirko Prato, Liberato Manna
We have developed a colloidal synthesis of nearly monodisperse nanocrystals of pure Cs4PbX6 (X = Cl, Br, I) and their mixed halide compositions with sizes ranging from 9 to 37 nm. The optical absorption spectra of these nanocrystals display a sharp, high energy peak due to transitions between states localized in individual PbX64– octahedra. These spectral features are insensitive to the size of the particles and in agreement with the features of the corresponding bulk materials. Samples with mixed halide composition exhibit absorption bands that are intermediate in spectral position between those of the pure halide compounds. Furthermore, the absorption bands of intermediate compositions broaden due to the different possible combinations of halide coordination around the Pb2+ ions. Both observations are supportive of the fact that the [PbX6]4– octahedra are electronically decoupled in these systems. Because of the large band gap of Cs4PbX6 (>3.2 eV), no excitonic emission in the visible range was observed. The Cs4PbBr6 nanocrystals can be converted into green fluorescent CsPbBr3 nanocrystals by their reaction with an excess of PbBr2 with preservation of size and size distributions. The insertion of PbX2 into Cs4PbX6 provides a means of accessing CsPbX3 nanocrystals in a wide variety of sizes, shapes, and compositions, an important aspect for the development of precisely tuned perovskite nanocrystal inks.
band gapCs 4 PbBr 6 nanocrystalsCsPbX 3 NanocrystalsMixed Halide Compositionsenergy peakbulk materialsperovskite nanocrystal inksPbBr 2halide coordinationhalide compositionsPbX 2size distributionsPbX 637 nmCsPbBr 3 nanocrystalshalide composition exhibit absorption bandsMonodisperse Insulator Cs 4 PbX 6nanocrystals displayexcitonic emissionCs 4 PbX 6absorption spectraaccessing CsPbX 3 nanocrystalshalide compoundsabsorption bands