Variations of energy band gap and magnetic properties upon quantum confinement effects on the Cr doped ZnO nanoparticles

Abstract

In this paper, Cr doped ZnO nanoparticles with different at % ratio (0, 2, 4, 6, 8, 10) (NPs) were synthesized with a precipitation method in ethanol. The synthesized nanoparticles have been analyzed using thermogravimetric analysis (TGA), x-ray diffraction (XRD), Energy dispersive x-ray spectroscopy (EDXS), transmission electron microscope (TEM), UV-vis spectrometer and Vibrating sample magnetometer (VSM) measurements. The XRD studies showed that the phase singularity of ZnO wurtizte hexagonal type structure. The surface morphology investigations by TEM confirmed the reduction of the particle size with increasing Cr content estimated from Williamson-Hall analysis of the diffraction peaks. The analysis of the UV-vis spectra of Cr doped NPs reveals that the wavelength of the absorption maxima λ max blue shifted to lower wavelength with increases the Cr content indicating the decrease in the particle size and recommends the increasing of energy gap with Cr content into ZnO semiconducting NPs. The observed increase of the energy band gap of Cr-doped ZnO nanoparticles caused by the decrease in the particle size with Cr concentration is attributed to the quantum confinement effect. The magnetization measurements showed room temperature ferromagnetism for all synthesized nanoparticles which can be attributed to the carrier-mediated exchange interaction improved by intrinsic defects.