Near Infrared Emission Band and Origin in Ni(II)-Doped CdS Nanoribbons by CVD Technique

In this work, we report the synthesis of high-quality Ni-doped CdS nanoribbons via chemical vapor deposition (CVD) method. The as-synthesized samples were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) techniques. The presence of Ni ions in CdS nanoribbons has been confirmed through energy-dispersive X-ray spectroscopy (EDX) and nonuniform peak shifting of Raman spectrum. Except the bandedge emission, the photoluminescence (PL) properties of Ni-doped CdS nanoribbons are dominated by a broad near-infrared (IR) emission band centered around 1.61 eV. This transition corresponds to two high levels of d electronic state of Ni with strong p-d hybridization between Ni ions and S, which seldom happens in usual dilute magnetic semiconductors (DMS). The p-d hybridization is confirmed by the simulation of electronic band structure in Ni-doped CdS wires with first-principle calculation and PL lifetime measurements, which blocked the optical transitions of lowest d levels. This near-IR emission shift with varied dopant concentration in Ni-doped CdS nanoribbons has been observed for the first time in this CdS semiconductors, which could be accounted for by the quantum confinement effect of NiS cluster in CdS; this material may be used as nanoscale light sources tuned by the dopant, possibly for solar cell if highly doped.