Synthesis And Optical Properties Of Al/Eu Co-doped ZnO Nanosheets

ZnO can be widely used for ultraviolet light-emitting diode and probe due to its excellentphysical, and chemical properties. In order to improve the optical property of ZnO, peopleadopt a lot of measures, such as trying a variety of different preparation methods, changingthe growth condition and annealing temperature to improve the UV emission and control thedefect luminescence. In general, for the actual application, its intrinsic luminescent propertiesof pure ZnO is not good enough. Fortunately, we can dope some impurities into ZnO to obtainexcellent properties. In this thesis, ZnO: Eu (ZEO) and ZnO: Eu Al (ZEAO) are prepared byhydrothermal method. Their structures, morphologies and properties of the as-preparednanosheets are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM),transmission electron microscopye (TEM), X-ray photoelectron spectroscopy (XPS),photoluminescence spectroscopy (PL) and ultraviolet and visible spectrophotometer(UV-Vis).Firstly, the graphene-like ZnO:Eu3+(ZEO) nanosheets with different Eu3+dopingconcentrations are synthesized successfully by a simple hydrothermal method. We can seethat all the diffraction peaks can be indexed to wurtzite-type ZnO structure for all the samples,no diffraction peaks are detected from europium oxides or any other impurities. The Eu3+doping concentration in ZnO probably increases with the increase of urea content. The SEMimages and TEM images show all the samples own nanoflake morphologies and a layer oflarge-area, continuous, crumpled and very thin sheet, which is quite similar to the graphenesheet. Besides the UV and green emission band in the PL spectra of ZnO:Eu3+nanosheets, wecan also observe an additional red emission peak centered at~613nm, which can be attributedto the intra-4f transition of Eu3+ions, in particular, the5D0–7F2transition. Red emission fromEu3+ions increase step by step with increasing the Eu3+content in the growth solution. Weutilize the native surface effect in the ZEO nanosheets for the first time to certify the resonantenergy transfer mechanism from the ZnO host to the Eu3+ions by means of thepower-dependent photoluminescence technique. Meanwhile, to further explore the functionalapplications of the graphene-like ZEO, we also characterize their photocatalytic activity onthe Rhodamine B dye and reveal that both the higher specific surface area and Eu3+dopinglead to the higher degradation efficiency of ZEO nanosheets.Then mesoporous films ZnO: Eu Al (ZEAO) are prepared through by hydrothermalmethod. We have systematically study different content of Al3+ions influence on the structure and performance of the samples. From the XRD patterns, we can see all the diffraction peakscan be indexed to wurtzite-type ZnO structure for all the samples. No traces of additionalpeaks from Eu, Al and other impurities are observed within the detect limitation. The decreaseof diffraction intensities indicates that the crystallization of samples deteriorates with theincrease of Al doping concentration. In the SEM and TEM images, The products appear innanosheets. When Al3+ions enter into the crystal lattice of samples, the grain growth of ZnOparticles is hindered, so the nanosheets become thinner. We can see that the sheets aremesoporous, in which the vacancies that balance the released molecules (H2O, CO2) cancondense to form voids in the nanosheet. From the PL images, we can find that the redemission peak becomes more and more intensity with the increase of Al3+ions, this may beattributed to two main reasons. One can be ascribed to the creation of oxygen vacancies dueto Zn2+sites occupied by smaller Al3+ions, the other can be ascribed to Al3+ionsincorporating into ZnO making the carrier concentration increase and Fermi level go up.In this paper, through doping Eu element into the lattices of ZnO, we obtain theefficient visible light emissions, and strongly enhance the intensity of red emission throughEu Al co-doped ZnO. Our results prompt the applications of ZnO: Eu Al nansheets in theoptoelectronic devices.