Synthesis and Characterization of Size-Tunable Colloidal InSb Quantum Dots with Optimized InP Shelling and Surface Passivation for Stable SWIR Emission

Abstract

Colloidal quantum dots (CQDs) offer unique advantages arising from size-dependent electronic structures and solution-processability, making them attractive materials for next-generation optoelectronic devices. Among the accessible spectral ranges, the short-wave infrared (SWIR, 1–2.5 μm) region has gained particular attention due to its intrinsically low scattering, high imaging contrast, strong penetration through haze and atmospheric interference, and minimal autofluorescence in biological tissues. Indium Antimonide (InSb) is a promising III–V semiconductor for long-wavelength SWIR emission owing to its narrow bandgap and large exciton Bohr radius, which allow strong quantum confinement and significant bandgap tunability even at relatively large particle sizes. However, colloidal InSb QDs have historically suffered from weak surface bonding and kinetic imbalance during growth, often leading to poor size control, while rapid surface oxidation creates deep trap states that strongly quench photoluminescence (PL). In this study, I introduce an integrated synthesis and surface-engineering strategy that effectively overcomes the intrinsic challenges of InSb quantum dots. By combining a single-source precursor with a continuous-injection approach, I achieved highly uniform InSb cores with precisely tunable long-wavelength optical properties, spanning 950 to 1550 nm. Using a single-source precursor combined with a continuous-injection approach, I synthesized highly uniform InSb cores with precisely tunable first-exciton absorption spanning 950–1550 nm. Immediately after core growth, an InCl₃ post-treatment was applied to stabilize the surface: Lewis-acidic In³⁺ species act as Z-type ligands to passivate electron-rich Sb dangling bonds, while Cl⁻ functions as a compact X- type ligand that helps displace weakly bound oxygen species and suppress further Sb–O formation. This cooperative passivation improves the optical quality and colloidal stability of the cores and provides a more robust surface for subsequent shell growth. To further suppress nonradiative pathways, I grew an InP shell on the InSb cores. By optimizing both the effective shell thickness and, critically, the shell-growth temperature, the PL intensity increased substantially and the emission peak became much sharper, consistent with improved shell crystallinity and reduced interfacial defects. The optimized shelling protocol was general across multiple core sizes and enabled long-wavelength SWIR emission, including PL beyond 1.5 μm and extending to ~2.0 μm for larger cores. Overall, the combination of InCl₃ surface reconstruction and optimized InP shell growth provides a reliable route to stabilizing InSb QDs and achieving long-wavelength SWIR emission up to 2000 nm. Through InCl₃ post treatment and well-defined shelling process, I was able to suppress deep surface and interfacial trap states, ultimately enabling stable SWIR emission reaching up to 2000 nm, a wavelength rarely accessible in colloidal III–V systems. Furthermore, introducing a thiol based ligand exchange dramatically improved oxidative stability. The treated QDs retained their PL for over 40 minutes under ambient conditions, demonstrating a level of robustness that is uncommon for narrow-bandgap III–V nanocrystals. Altogether, this comprehensive synthetic framework establishes a reliable route to high-quality, long- wavelength InSb-based emitters, pushing the performance of colloidal SWIR quantum dots beyond what has previously been achieved. Overall, this work provides a practical and reproducible pathway for producing InSb-based colloidal QDs that simultaneously achieve long-wavelength SWIR emission and high chemical stability. These advances position InSb/InP QDs as promising platform materials for a wide range of SWIR applications, including autonomous-vision and night-vision sensors, high-sensitivity SWIR photodetectors, medical and security imaging, and long-distance optical communication.