Structure, photoluminescence, and magnetic properties of Co-doped ZnO nanoparticles

Co-doped ZnO-nanoparticles were synthesized using the sol–gel method. The microstructure, morphology, and physical properties of the particles were studied using several analytical methods, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis absorption spectroscopy, photoluminescence spectrometry, and vibrating sample magnetometry. The structure of the Co-doped ZnO nanoparticles was identified as hexagonal wurtzite, which suggests that Co²⁺ can replace the Zn²⁺ sites in the ZnO crystal lattice without forming a secondary phase. For Co-doped samples, the optical energy bandgap decreased with an increase in the Co content. The absorption-band edges were 565, 610, and 653 nm, which correspond to the d–d transition of Co²⁺ ions in the tetrahedral field of ZnO. The PL spectra revealed a strong defect-emission, which indicates that defects may stabilize the ferromagnetic order. Room-temperature ferromagnetism was observed in Co-doped ZnO nanoparticles according to M–H measurements. Furthermore, the magnetization increased with increasing Co concentration. These findings suggest that Co-doped ZnO nanoparticles could promote the development of semiconductor devices with ferromagnetic properties above room temperature in magneto-optical and spintronic applications.