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Pure and vanadium (V) doped ZnO nanoparticles (NPs) were successfully synthesized via a modified sol-gel method. The wurtzite crystal structure of ZnO remained intact with the vanadium doping concentrations under the present synthesis environment as confirmed by an array of advanced analytical techniques; such as Rietveld refined X-ray diffraction (XRD) pattern, as well as bond valence sum (BVS) analysis. SEM and TEM techniques were used to examine the morphology of the samples. UV-Vis-NIR spectra showed an absorption band in the UV range with reduction in the band gap from 3.23 eV to 3.20 eV when V content increases. Photoluminescence (PL) shows that doping with V causes the creation of some defects in the band gap of ZnO. The energy position of the obtained PL emission introduces a blue shift when the measurement temperature increases. The M-T curve is successfully fitted using both three dimensional (3D) spin wave model and Curie-Weiss law which attests to the mixed state existence of ferromagnetic (FM) and paramagnetic (PM) phases. The electron paramagnetic resonance (EPR) analysis supports the XRD results and provides evidence of oxygen vacancies (V O). Magnetic interaction is quantitatively studied and explained by polaronic percolation of bound magnetic polarons (BMP) produced by V O defects. [Display omitted] • Pure and Vanadium (V) doped ZnO nanoparticles were successfully synthesized via a modified sol-gel method. • The crystal structure of samples was determined by Rietveld XRD method. • The size and homogeneity of the crystallites were influenced by the amount of vanadium dopant used. • The existence of Oxygen vacancies and related complex defects is verified. • Formation of Bound magnetic polarons and mixed magnetic characteristics are observed. [ABSTRACT FROM AUTHOR]

Effects of Co doping on the structural and optical properties of ZnO oxide nanoparticles (NPs) prepared by a solvothermal method are reported. X-ray diffraction examinations using Rietveld refinement confirms the hexagonal wurtzite symmetry ZnO phase nanostructure belonging to P6 3 mc space group. No segregated secondary phases or Co rich clusters were detected. The X-ray diffraction peaks shifts towards higher angle gradually as the concentration of nominal Co content increases in ZnO. This shifting in peak position reflect that Co is well replaced Zn in ZnO matrix. With increasing the Co content to 3%, both lattice parameters a and c of the hexagonal ZnO tended to gradually decrease, suggesting substitutional doping of Co at the tetrahedral Zn2+sites. For Co loading of5%, these trends reversed and the lattice showed a gradual expansion, which is explained by additional interstitial incorporation of Co. The Williamson-Hall (W–H) method with various models i.e. uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM), as well as size-strain plot (SSP) method, and the morphological observations using transmission electron microscopy (TEM) image were used to evaluate the crystallite size as well as the lattice strain. Optical studies carried out by diffuse reflectance spectroscopy (DRS) indicated a decrease in the value of the band gap from 3.238 eV to 2.993 eV with increasing Co doping concentration. The obtained results are confirmed by cathodoluminescence technique. • Co doped ZnO nanoparticles were synthesized by a modified sol–gel process. • The band gap goes from 3.238 eV to 2.993 eV with rising Co content. • The cathodoluminescence demonstrates the enhancement of native defects with Co loading. • Structural study explain well the CL peaks. • The presence of cobalt enhance the oxygen vacancy and zinc vacancy concentrations. [ABSTRACT FROM AUTHOR]