Sol–gel synthesis and defect engineering in Mg-, Co-, Ni-, and In-doped ZnO nanoparticles for UV photodetector and spintronic applications: a combined PL, VSM, PAS, DBS, and DFT study

In this work, ZnO nanoparticles doped with Mg, Co, Ni, and In were synthesized using a sol–gel auto-combustion method to examine how different dopants influence their structural, optical, magnetic, and photodetection behavior. XRD and FESEM analyses were employed to determine the crystal structure and surface morphology. PL and VSM measurements were performed to evaluate the optical emission and magnetic characteristics in relation to defect states, respectively. At the same time, positron annihilation spectroscopy (PAS) and high-resolution Doppler broadening spectroscopy (DBS) were used to identify defect concentrations directly. Additionally, DFT calculations were performed to provide a deeper theoretical understanding of the experimentally observed variations in electronic, optical, and magnetic characteristics, particularly in relation to intrinsic defects responsible for photon emission and room-temperature ferromagnetism. Overall, the enhanced crystal quality, lower carrier concentration, and increased saturation magnetization confirm that suitably doped ZnO nanoparticles are promising materials for the development of advanced UV photodetectors and spintronic applications.