Electrical, photoluminescence and optical investigation of ZnO nanoparticles sintered at different temperatures

We report here structural, electrical, photoluminescence (PL), and optical investigations of ZnO nanoparticles. The ZnO samples are initially sintered at various temperatures (T-s) (600-1200 degrees C) temperatures and their size is reduced twice to nanoscale by using ball friction at 200 rpm rotational speed and 30 min duration. It is found that the T-s do not influence the well-known peaks associated with the ZnO hexagonal structure, whereas the constants of the lattice and the average crystallite diameters are affected. Although the nonlinear area is observed for all samples in the I-V curves, the breakdown field E-B and nonlinear coefficient beta are moved to lower values as T-s increases, while the residual voltage K-r and nonlinear conductivity (sigma(2)) are increased. The empirical relations for K-r, E-B, and beta as a function of T-s are; K-r = 0.004 T-s - 0.487, E-B = - 1.786 T-s + 2559.5 and beta = - 0.052 T-s + 75.19. On the other hand, a maximum UV absorption shift (A(max)) is obtained at 412 nm, 400 nm, 384 nm, and 326 nm as the T-s increases up to 1200 degrees C. For each sample, two different energy band gap values are obtained; the first is called the basic bandgap (E-gh) and its value above 3 eV, while the second is called the optical band gap (E-gL), and its value below 2.1 eV. Moreover, the empirical relations of them are E-gh = 0.002 T-s - 0.24, E-gl = - 0.0033 T-s + 5.242 and increment E =- 0.0015 T-s + 5.002. Furthermore, the values of (N/m*) and lattice dielectric constant epsilon(L) are increased by increasing T-s up to 1200 degrees C, while the vice is versa for the interatomic distance R. The dielectric loss tan delta is almost linear above 4 eV for all samples, and it decreases sharply as the T-s increases. The optical and electrical conductivities sigma(opt) and sigma(ele) are decreased as the T-s increases up to 1200 degrees C. Finally, the characteristic of UV band edges against the optimum value of PL intensity for the samples shows 8-continuous peaks. Furthermore, the PL intensity of the peaks is decreased by increasing T-s and also by shifting the UV wave number towards the IR region.