Tailoring luminescent and magnetic characteristics of Cu-doped CdSSe quantum dots for optomagnetic applications

Copper-doped ternary alloyed semiconductor quantum dots (QDs) are promising multifunctional nanomaterials owing to the synergistic combination of composition-dependent band-gap engineering and dopant-induced optical and magnetic functionalities. Despite extensive studies on Cu-doped binary CdS and CdSe QDs, investigations of Cu-doped ternary CdSSe QDs remain unexplored. In this work, CdSSe and Cu-doped CdSSe QDs with Cu concentrations ranging from 1 to 10% were successfully synthesized via a wet-chemical route. X-ray diffraction and Rietveld refinement analyses confirmed the formation of a single-phase zinc blende structure without detectable secondary phases. The diffraction peaks systematically shifted toward higher diffraction angles with increasing Cu content, accompanied by a reduction in the lattice parameter from 5.96 to 5.85 Å, indicating lattice contraction caused by the substitution of Cd²⁺ ions by smaller Cu²⁺ ions. Transmission electron microscopy revealed nearly spherical nanoparticles with average sizes increasing from approximately 3.5 to 5.0 nm upon Cu incorporation. The absorption peak exhibits a progressive blue shift, while the optical band gap increases from 2.48 to 2.83 eV as the Cu concentration increases from 0 to 10%. Cu doping creates defect-related radiation centers, leading to strong emission in the long wavelength region. The average lifetime increased sharply from 16.26 ns for undoped CdSSe QDs to 882.57 ns for CdSSe:Cu 10% QDs, demonstrating efficient carrier localization at Cu-related impurity levels. Magnetic measurements revealed that Cu doping significantly altered the magnetism of CdSSe QDs by generating local magnetic moments associated with the 3d state of Cu. This study demonstrates that Cu doping can simultaneously control the luminescence and magnetic properties of CdSSe QDs, making them attractive candidates for advanced optoelectronic and spintronic applications.