Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics

The tunability of structural, optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising materials for multiple spintronic and optoelectronic applications. However, controlling the size of QDs to tune these properties is challenging due to their quantum size and high sensitivity to the ambient atmosphere. Here, we demonstrate successfully synthesized tunable Mn-doped cadmium sulfide (0% ≤ Mn ≤ 6%) diluted magnetic semiconductor QDs by hot injection chemical route. XRD and TEM studies confirmed that undoped and Mn-doped CdS QDs are polycrystalline in cubic phase without having any dopant-related signature. The XPS study shows the spin–orbit split due to Mn-doping and the atomic percentage of each element present in the prepared sample has been calculated from XPS data. XANES (X-ray Absorption Near Edge Structure) study shows that the Cd has the same oxidation state (+2) in the undoped and Mn-doped CdS QDs and also Mn has +2 oxidation state in Mn-doped CdS QDs. Extended X-ray Absorption Fine Structure (EXAFS) measurements show local structural disorder in higher doping concentration of Mn. It also shows that due to Mn doping, the coordination number of S in all the Mn-doped samples have the S vacancy compared to undoped CdS. No significant change has been observed in FTIR spectra after Mn doping. Raman spectra exhibits two longitudinal optical (LO) modes at 299 cm −1 and 598 cm −1 . The intensity of the first LO peak decreases rapidly and linearly due to local structural and short-range disorder induced with increasing Mn concentration in CdS. UV–Vis spectroscopy reveals non-linear variation of bandgap energy showing the downwards bowing with increasing Mn-doping concentration. PL and TRPL indicate appearance of surface defect states with Mn-doping. TRPL spectra show decrease in decay time due to Mn‐doping. Room temperature ferromagnetism of Mn-doped CdS QDs confirms the diluted magnetic semiconductor behavior, which would play key role in quantum spintronics.