Estudo teórico-experimental de nanoestruturas de ZnO dopado com íons níquel(II) e cromo(III)

Abstract

In this study samples of pure ZnO, Zn1-xMxO (M = Ni2+ and Cr3+) and Zn1-2xNixCrxO (x= amount at mol of M) were prepared by hydrothermal microwave assisted method. The materials were obtained at 100 °C, heating rate of 5 °C min -1 and 4 minutes of time. The results of XRD and Rietveld refinement showed the formation of the wurtzite phase for all samples indicating a periodic structural organization at long range. FESEM images showed that doping directly influences the morphology of the materials. For the samples of ZnO doped with Ni2+ were observed formation of elongated particles with initial type flower morphology, while the inclusion of Cr3+ ions leads to a directional growth of the nanoparticles to start formation nanorods of varying sizes. The UV-Vis spectra showed absorption bands pertaining to the transitions of the dopant ions Ni2+ and Cr3+. The Raman spectroscopy measures the vibrational active modes of wurtzite structure of ZnO were observed in all materials. It was found that after the doping with Ni2+ and Cr3+ there was a decrease in the intensity of the characteristic band of wurtzite structure showing a structural disorder at close range, especially for samples doped with Cr3+. The samples showed photoluminescence properties with maximum emission in the area of green-orange of the visible spectrum, which are related to structural defects medium and short-range in the crystalline ZnO lattice. The introduction of the ions in the structure caused a decrease in the intensity of luminescence compared to pure oxide. The theoretical calculation results show that the mBJ+UZn approach allows better describe the electronic structure zinc oxide. It was obtained a gap value similar to observed in experimental measures. The insertion of dopants caused structural changes in the ZnO lattice and 3d levels were introduced between the valence band and the conduction band responsible for reducing the value of the gap. For samples Zn1-xCrxO were observed greater structural distortions according to the measured Raman spectroscopy. In the co-doped system was observed a synergism between the dopants responsible to a reduction in the total magnetization of the system.