Modification Of ZnO-based Composites

Zine Oxide (ZnO), a typical wide bandgap Ⅱ-Ⅵ semiconduetor material with a good photoelectric properties, which has a wide-direct-band gap of3.37eV and large exciton binding energy of～60meV, is a promising application in the fields of optics, electrics and magnetics. First, The binding energy of ZnO is higher than room thermal energy, so it has a good excitonic emission performance at room temperature. Zinc oxide is very promising in the development of ultraviolet emitting devices. Second, the Curie temperature(Tc) of ZnO-based dilute magnetic semiconductor material is higher than the room temperature. These outstanding features make ZnO-based dilute magnetic semiconduetor a important material in information processing and storage. Third, the serious environmental pollution and increasing population make the quality of drinking water be a major concern of the world. ZnO is a effective photocatalyst in organic dye degradation and wastewater treatment. Due to these excellent properties, ZnO has many potential applications. We have done some related research work in this background.(1) MgO coating ZnO microrods were synthesized by hydrothermal growth method in a two-stage process. The excitation-dependent photoluminescence of uncoated and MgO-coated ZnO microrods was investigated. We found that the MgO coating passivates defect-states on the surface to reduce largely the green emission, thus the ultraviolet emission efficiency is improved significantly. In addition, the monotonous dependences of violet and ultraviolet emissions on excitation wavelengths are found firstly, while the blue and green emissions are likely in saturated states and are nearly independent of excitation wavelengths. This phenomenon can be interpreted by the transition mechanisms and it indicates that the excitation tuning can also be used to further improve ultraviolet emission efficiency.(2) The optical and magnetic properties of Zn1-xCuxO (x=0.0-3.5%) nanocrystals fabricated via a simple sol-gel method have been investigated in detail. X-ray diffraction, optical absorption and photoluminescence spectra were employed to validate consistently the incorporation of Cu ions into the ZnO wurtzite lattice without formation of other second phases for Zn1-xCuxO (x<2.0%). Moreover, it was found that the substituted Cu-doping led to the reduction of the band gap and the appearance of the structured green emission. Magnetization measurement revealed that the low Cu-doping (x<1.0%) developed the ferromagnetism, but the high Cu-doping destroyed sharply the ferromagnetism due to the formation of the antiferromagnetic coupling among the neighboring Cu ions.(3) ZnO coating Fe3O4particles were synthesized by hydrothermal growth method in a two-stage process.In the second stage, we used deionized water and absolute alcohol to get different forms of ZnO coating Fe3O4particles. Different characterization tools, such as transmission electron microscope (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) were employed to establish the morphology, structural and magnetism of the material. The particle of this form can be well used in organic dye degradation and wastewater treatment. But for using in biological markers,we need to synthesis smaller Fe3O4particles.