Optical properties of diluted magnetic semiconductor Cu:ZnS quantum dots

Abstract

Herein quantum dots (QDs) of diluted magnetic semiconductor Cu:ZnS have been synthesized via a simple chemical synthesis method. A single phase solid solution is formed up to x=0.1 which confirmed by using X-ray diffraction. Crystal structure and microstructure analyses were performed by Rietveld refinement. Photoluminescence (PL) emission spectra were recorded for pure and Cu doped ZnS QDs excited at 268 and 228nm respectively. PL emission and excitation spectra were investigated in different wavelength regions within the range of 200–900nm. PL results in the range of 220–300nm emission band reveals that the band gap of pure ZnS QDs is about 4.43eV which greater than that of bulk ZnS (3.7eV). The band gap of Cu:ZnS QDs is tunable with Cu content (x) as well as the crystalline size, and it is peaked around 4.47eV. PL emission in the range of 350–650nm exhibits a green fluorescence band peaking around 552nm for pure ZnS QDs, which confirms the characteristic feature of Zn2+ as luminescent centers in the lattice, while blue emission bands peaked around 471nm for Cu:ZnS QDs that is attributed to the transition of electrons from conduction band of ZnS to the Cu impurity level. The blue shift of the absorption peak directly reflects the effect of quantum confinement. The PL results have been supported by X-ray phase analysis, high-resolution electron microscopy (HRTEM and SEM), compositional evaluation (EDX) and magnetic measurements (VSM).