Abstract
<title>Abstract</title> <p> This work reports a fundamental breakthrough in the design of ligand-free, thermally robust quantum light emitters for silicon-integrated optoelectronics and deep-tissue imaging. We demonstrate that magnetite (Fe <sub>3</sub> O <sub>4</sub> ) colloidal quantum dots (CQDs) can be synthesized via thermodynamically guided (110) facet-assembly in an aqueous phase. Subsequent sulfurization at 140°C converts these templates into greigite (Fe <sub>3</sub> S <sub>4</sub> ) CQD molecules while preserving their facet-fused architecture. Simultaneous absorption/emission spectroscopy reveals the formation of electronic minibands resulting from resonant wave-function overlap between fused CQDs, enabling intense near-infrared (NIR) emission at 1771 nm. This "CQD molecule" architecture offers four transformative advantages: (1) Scalability: A robust, aqueous synthesis demonstrated at 0.5 m <sup>3</sup> volumes; (2) Ligand-free coupling: Facet-guided fusion enables closer proximity and stronger electronic coupling than traditional ligand-exchange methods; (3) Magnetic stabilization: The spinel ferrimagnetic lattice protects exciton spins, suppressing dephasing and enabling room-temperature quantum coherence; and (4) Biocompatibility: A toxic-element-free composition suitable for sensitive biomedical applications. This approach provides a viable pathway for integrating high-performance quantum emitters directly into existing semiconductor foundries via covalent sulfur-bridge immobilization. </p>