Air-Stable Short-Wave Infrared Tin Telluride and Tin Telluride/Zinc Telluride Core–Shell Colloidal Quantum Dots

Abstract

To date, colloidal quantum dots (CQDs) with absorption in the short-wave infrared region (SWIR, 1–2.6 μm) typically consist of hazardous cadmium, lead, or mercury chalcogenides, which limit commercial acceptance. Environmentally friendly alternatives are therefore required to ensure minimal damage to ecosystems during fabrication, use, and disposal. A promising hazardous-element-free SWIR absorbing nanomaterial candidate is tin chalcogenide. We have developed tin telluride (SnTe) CQDs, with a size ranging from ∼17 to 26 nm and corresponding absorption peak from ∼2.3 to 2.5 μm, indicative of size-dependent quantum confinement. Air-stable tin salts (tin chloride or tin acetate) were employed instead of the typical air-sensitive bis(bis(trimethylsilyl)amino tin(II). The synthesis was systematically investigated by optimizing the ligand type (1-dodecanethiol was used to replace oleic acid to prevent oxidation), injection method, growth temperature, reaction time, and feed molar ratio between tin and tellurium precursors. To improve stability in air, a ZnTe shell was successfully synthesized via cation exchange reaction at 70 °C with zinc acetate. The SnTe/ZnTe core–shell nanocrystals were fully characterized, revealing the formation of a protective ZnTe shell with a thickness of two to three monolayers, resulting in long-term stability in air (up to 1 month). These air-stable CQDs may offer a low-toxicity alternative nanomaterial for low-cost solution-processable fabrication of SWIR optoelectronics.