Phase-Selective Synthesis of Zn₃Sb₂ and ZnSb Quantum Dots via Temperature-Controlled Zn-Loss-Mediated Reconstructions

Group II-V Zn-Sb semiconductors have attracted attention as a class of materials that combine relatively low toxicity, excellent thermoelectric properties, and narrow band gaps. However, the colloidal synthesis of quantum dots (QDs) with precisely controlled phase and stoichiometry at the few-nanometer scale has remained very limited. In this study, we demonstrate the colloidal synthesis of Zn₃Sb₂ and ZnSb QDs with accurately controlled stoichiometry by simply tuning the reaction temperature, without using any additional reducing agents. Zn₃Sb₂ QDs (2.7 ± 0.1 nm) exhibit an optical band gap of 1.22 eV, whereas ZnSb QDs (6.6 ± 0.3 nm) show a band gap of 0.86 eV. Based on these values, we construct the band alignment between Zn₃Sb₂ and ZnSb QDs. We further propose a Zn-loss-driven phase-transition mechanism from Zn₃Sb₂ QDs to thermodynamically more stable ZnSb QDs. This phase-transition behavior and the associated electronic structure provide important insights into phase stability and composition control strategies in Zn-Sb nanocrystals. Moreover, the broad NIR absorption, narrow band gaps, and facile composition/phase tunability of Sb-based group II-V Zn-Sb QDs suggest that they are promising low-toxicity material platforms for energy and optoelectronic applications such as NIR photodetectors, solar cells, and thermoelectric devices.