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Near-infrared emitting colloidal two-dimensional (2D) PbX (X = S, Se) nanoplatelets (NPLs) have emerged as interesting materials with strong size quantization in the thickness dimension. They act as model systems for efficient charge carrier multiplication and hold potential as intriguing candidates for fiber-based photonic quantum applications. However, synthetic access to the third family member, 2D PbTe, remains elusive due to challenging precursor chemistry. Here, we report a direct synthesis for 2D PbTe NPLs with tunable photoluminescence [PL, 910–1460 nm (1.36–0.85 eV), PL quantum yields 1–15%], based on aminophosphine precursor chemistry. Ex situ transamination of tris(dimethylamino)phosphine telluride with octylamine is confirmed by 31P nuclear magnetic resonance and yields a reactive tellurium precursor for the formation of 2D PbTe NPLs at temperatures as low as 0 °C. The PL position of the PbTe NPLs is tunable by controlling the Pb/Te ratio in the reaction. Grazing-incidence wide-angle X-ray scattering confirms the 2D geometry of the NPLs and the formation of superlattices. The importance of a postsynthetic passivation of PbTe NPLs by PbI2to ensure colloidal stability of the otherwise oxygen-sensitive samples is supported by X-ray photoelectron spectroscopy. Our results expand and complete the row of lead chalcogenide-based 2D NPLs, opening up new ways for further pushing the optical properties of 2D NPLs into the infrared and toward technologically relevant wavelengths.

Corona-producing cirrus clouds were generated and measured under chamber conditions at the AIDA cloud chamber in Karlsruhe. We were able to measure the scattering properties as well as microphysical properties of these clouds under well-defined laboratory conditions in contrast with previous studies of corona-producing clouds, where the measurements were conducted by means of lidar and in situ aircraft measurements. Our results are in agreement with those of previous studies, confirming that corona-producing cirrus clouds consist of a narrow distribution of small (median D_p=19–32  μm) and compact ice crystals. We showed that the ice crystals in these clouds are most likely formed in homogeneous freezing processes. As a result of the homogeneous freezing process, the ice crystals grow uniformly in size; furthermore, the majority of the ice crystals have rough surface features.