The unique properties of indium antimonide (InSb) make nanostructures of this III-V semiconductor promising material platforms for a large variety of optoelectronic devices that could potentially outperform those based on other semiconductors. InSb possesses a narrow direct band gap (0.17 eV at 300 K), a giant g-factor (-51.3), strong spin-orbit coupling, and the highest room temperature electron mobility, lowest thermal conductivity, and smallest exciton binding energy of all semiconductors. These properties make it ideal for infrared detectors, ultrafast electronics, thermoelectric power conversion, spintronics, and quantum computing. Moreover, owing to the large exciton Bohr radius of InSb (61 nm), quantum dots (QDs) of this material are obtained already at relatively large nanocrystal sizes and allow widely tunable bandgaps in the near-IR spectral range through size control. Given the inherent advantages of colloidal synthesis methods, this would allow the use of colloidal InSb QDs as building blocks in low-cost, solution-processed optoelectronic devices, such as field-effect transistors, photodetectors, thermoelectric devices, LEDs, and solar cells, as well as non-toxic labels for deep-tissue imaging.

Despite the unparalleled potential of colloidal InSb QDs, their synthesis has proven to be very challenging, and thus remains underdeveloped with respect to that of II-VI, IV-VI, and other III-V QDs, despite recent advances [1-3]. In this work, we use Lewis acid-base interactions between Sb(III) and In(III) species formed at room temperature in situ from commercially available compounds (viz., InCl₃, Sb[NMe₂]₃ and a primary alkylamine) to obtain InSb adduct complexes. These complexes are successfully used as precursors for the synthesis of colloidal InSb QDs ranging from 2.8 to 18.2 nm in diameter by fast co-reduction at sufficiently high temperatures. Our findings allow us to propose a formation mechanism for the QDs synthesized in our work, which is based on a non-classical nucleation event, followed by aggregative growth. This yields ensembles with multimodal size distributions, which can be fractionated in sub-ensembles with relatively narrow polydispersity by post-synthetic size fractionation. The QDs exhibit photoluminescence with small Stokes shifts and short radiative lifetimes, implying that the emission is due to band-edge recombination and that the direct nature of the bandgap of bulk InSb is preserved in InSb QDs. Finally, we constructed a sizing curve correlating the peak position of the lowest energy absorption transition with the QD diameters, which shows that the band gap of colloidal InSb QDs increases with size reduction following a 1/d dependence.