Structural, optical and magnetic studies of co-doped mesoscopic ZnO nanoparticles

In this work, we report co-doping of two types of magnetic ions in ZnO nanoparticles with the generic formula TM _x ¹ TM _x ² Zn_(1-2x)O (x = 0.025, 0.05 and 0.1), where TM indicates transition metal. X-ray diffraction studies confirms the phase purity of synthesized nanoparticles. All the samples show hexagonal wurzite crystal structure. No impurity peaks were observed within the X-ray diffraction limit. Spherical nanoparticles with uniform size ranging from 22 to 23 nm were observed using field emission scanning electron microscopy. Band gap ranging from 3.26 to 3.40 eV were calculated by using UV–Vis spectroscopy. Photoluminescence spectroscopy shows the presence of defect structures due to oxygen vacancies in the nanoparticles. Raman spectra confirm the crystallinity of the sample observed from the Raman mode at 437 cm⁻¹. In Raman spectra, the broadening observed in the region 1,100–1,500 cm⁻¹ which was attributed to multiphonon modes which also confirmed the presence of defects in synthesized nanoparticles. All the co-doped samples show a paramagnetic behavior. Weak ferromagnetic behavior starts appearing for samples with x = 0.1. This ferromagnetism is attributed to the additional impurity phases in the sample.