Effect of Gd doping concentration and sintering temperature on structural, optical, dielectric and magnetic properties of hydrothermally synthesized ZnO nanostructure

Nanoparticles of Gd3+ ions doped ZnO were prepared by hydrothermal method. To obtain the desired nanocrystalline phase and also, to enhance the oxygen vacancy inside the host ZnO nanoparticles, the as prepared sample is sintered at 400 and 600 °C for 2 h in vacuum atmosphere. X-ray diffractograms (XRD) analysis reveals the absence of any impure phases in the Gd3+ ions doped ZnO nanostructure. The presence of intrinsic defects/oxygen vacancies were confirmed by the analysis of UV-Visible, PL and Raman spectra of the doped sample. The qualitative and quantitative analysis of intrinsic defects was successfully explained by three-state trapping model using positron annihilation study. Room temperature ferromagnetism was found in the sample of 5% Gd3+ ions doped ZnO, which has been successfully explained by the vacancy assisted bound magnetic polaron model. Frequencies as well as temperature dependent dielectric constant of the samples were investigated. The dielectric constants were recorded at 40 Hz and 100 kHz frequencies and the values are nearly ∼2.76 х 106 and 12782 respectively, in the 5% Gd3+ ions doped ZnO sample.