Solving the Synthetic Riddle of Colloidal Two-Dimensional PbTe Nanoplatelets with Tunable Near-Infrared Emission

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.