Investigations on absorption, photoluminescence and magnetic properties of ZnO: Co nanoparticles

Abstract

We have investigated the consequences of cobalt (Co) incorporation with different doping concentrations (0, 2, 4 and 6 %) on structural, optical and magnetic properties of ZnO nanoparticles. The results of X-ray diffraction spectra (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern of single particle, energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared (FT-IR) authenticate the substitution of cobalt and hexagonal crystal structure without any secondary phase formation of all the samples under investigation. The ultraviolet–visible (UV–Vis) absorption study indicates that increase in Co concentration improves the visible region absorption (550–700 nm). The absorption edge of Co-doped ZnO shifts towards visible region with increase in Co concentration. The band gap of samples shows a red shift with increase in Co percentage. The photoluminescence (PL) study of the samples indicates that Co doping shifts the intense peak position of ZnO from violet to blue colour. The weak emission peak at 572 nm is also observed in all the samples. The emission is represented by chromaticity diagram. The room temperature magnetic properties have been studied using vibrating sample magnetometer (VSM). The room temperature magnetisation curve shows that an increase in Co concentration increases the linear behaviour of M–H loop. The magnetic susceptibility results indicate that all the samples have Curie–Weiss behaviour. The coercive field (Hc) and the remanence magnetisation (Mr) increase with Co doping concentration. Fig. M–H curve of pure and cobalt-doped ZnO nanoparticles at 300 K. Inset (a) shows absorption spectra, and inset (b) shows the emission spectra of Zn1−x Co x O nanoparticles.