| Zinc oxide (ZnO), as a semiconductor with a wide band-gap (3.37eV) in roomtemperature and high exciton binding energy (60meV), has important potentialapplications in short-wave photoelectricity devices, photocatalysis and photodecectorsas a result of its excellent electricity and optical properties. After a long time researchfor pure ZnO, the investigation on the properties of doping ZnO has been a new hotspotattracting the attentions of many researchers. However, there were some questions anddifficulties lying in way of practically applying ZnO, such as that intrinsic luminescentintensity cannot reach the level of practical application and the main emission peakslocating in ultraviolet range doesn’t satisfy the practical requests of flat panel displays.In consideration of it, the effects on ZnO optical properties of Y/Cu and Y-Cd/Y-Cudoping were discussed, and also the aspect of enhancing ZnO’s UV and deep-levelemission was researched in this dissertation.Sol-gel method was applied to prepare Y/Cu doping ZnO nanoparticles andchemical co-precipitation method was using to prepare Y-Cd/Y-Cu doping ZnOsamples. Then X-ray diffraction (XRD) was used for testing samples and all the resultsshows that doped samples belonged to the ZnO with hexagonal wurtzite structure. Andthe X-ray photoelectron spectroscopy (XPS) demonstrated the existence of dopingelements in ZnO lattice. At the same time, the grain diameter of ZnO and morphologywere observed by applying TEM and FESEM. The optical properties were confirmedby photoluminescence specta (PL). We can make some conclusions as follow:1. Via analyzing the XRD spectra, it can figure out that the largest solid solubility ofyttrium in ZnO lattice is6.12at%, and the PL spectra shows that yttrium can efficiently enhance ZnO’s UV emission and depress the DLE. When x(Y)=7at%,the effect of yttrium in ZnO reaches a climax: the UV emission intensity ofZn0.93Y0.07O is nine times of that of pure ZnO, and the value of IUV/IDLEis high to32.2. Doping Cu into ZnO can decreases UV emission and enhances the DLE intensity.It could be explained that Cu can form an impurity center in ZnO lattice and behavelike a trap for nonequilibrium holes or electrons, split the band structure, whichenhanced the probability of failure in the recombination of holes and electrons, i.e.,non radiative excitonic transitions from defect states become more prevalent,therefore, enhance the visible emission. When the copper concentration is greaterthan5at%, DLE intensity becomes stronger than the UV emitting. Enhanced visibleemission makes it possible which Zn1-xCuxO system can be developed applicationinto photocatalysis.3. The Y-Cd co-doping effect on ZnO optical properties was also explored. Keepingyttrium concentration invariant, we increased cadmium concentration and observedthat UV emitting peak red shifted gradually and emission intensity was seriouslyweakened at the same time; on the other hand, we kept cadmium concentrationinvariant and increased yttrium concentration, found that the UV intensity increasedwith the increase of Y and x(Y)=7at%was at its maximum. In one of the PL spectra,intensities in different positions showed quite different, and the reason could beexplained that several steps in the experimental process may be in charge of it.Finally, the optimized doping scheme is x(yttrium)=7at%and x(cadmium)=3at%,that is, Zn0.90Y0.07Cd0.03O, whose UV emission intensity and peak location reachedthe optimum.4. Co-doping of Y-Cu refined the ZnO nanopowders’grain sizes. We used FESEM toobserve the morphologies of the samples and found that the grains grown aschuzzles with a diameter of2~3μm which the length and width of fluffs on thechuzzles were1μm and50~100nm, respectively. The co-doped ZnO PL spectrashows that a small amount concentration of Cu mighty depressed UV emitting andstrengthened the visible emitting. It may be accounted for that in the process of Y and Cu competing carriers, Cu acts as a powerhouse and depletes more carriers thanY can donate. |
PDF Full Text Request