Vacancy-driven improvement of optical and ferromagnetism in Co2+/La3+ dual-doped ZnS quantum dots for spintronic and optoelectronic applications

This study presents a novel investigation of the combined effects of Co 2+ and La 3+ dual-doped ZnS quantum dots (QDs) on their microstructural, magnetic, and optical properties, relevant to spintronic and optoelectronic applications. A straightforward chemical approach (co-precipitation method) was used to synthesize Zn 0.90 Co 0.1-x La x S quantum dots (x = 0, 3, 5, and 7 at.%) capped with polyethylene glycol (PEG) to regulate the size of the QDs. A cubic single-phase structure with almost uniform spherical particles averaging around 6–7 nm in size was evidenced by X-Ray Diffractometer (XRD) and High-Resolution Transmission Electron Microscope (HR-TEM), complemented by Selected Area Electron Diffraction (SAED). The X-Ray Photoelectron Spectroscope (XPS) outcomes showed the incorporation of Cobalt and Lanthanum elements in both the (+2) and (+3) oxidation states, and also highlighted a substantial presence of sulfur vacancies. The tunability of the optical gap energy (E g ) and the optical dispersion parameters (E d , E o ) has resulted in an improvement of the non-linear optical attributes, thereby supporting their application in optoelectronic devices. Defect-assisted blue emission was monitored through a Photoluminescence (PL) investigation. Furthermore, the dual-doping improves the room-temperature ferromagnetic ordering (RT-FM), possibly mediated by vacancy-induced magnetic polarons. These compelling magnetic results suggest that dual-doped ZnS QDs could pave the way for advancements in spintronic technology.