Growth Mechanism And Optical Properties Of Low Dimensional Zno Crystals And Their Composite Nanomaterials

Low-dimensional ZnO nanocrystals and their composite nanomaterials have superior physical properties and wide applications.They form an important research area concerning the low-dimensional semiconductor physics.ZnO is a direct bandgap semiconductor with a bandgap of 3.37 eV.It has an exciton binding energy of 60 meV and can be used to construct ultraviolet lasers working at room temperature.ZnO usually has zinc blende structure.Its nanostructures have fruitful morphologies.The low-dimensional ZnO nanocrystals and their composite nanostructures can be fabricated by using the chemical solution-synthesis method.The study of the crystal growth mechanisms and optical properties of the ZnO nanocrystals and composite nanostructures not only has scientific meanings but also can pave the way for their applications in devices.We study the crystal growth of the ZnO nanocrystals in the solution by using the transmission electron microscopy.The ZnO nanoparticles show oriented attachment during their growth process.By using the theoretical study and calculation,we find that the spontaneous polarization force dominates the crystal growth of the ZnO nanoparticles.This helps to improve our understanding of the crystal growth mechanism of the nanocrystals in the solutions.We synthesize the ZnO quantum dots by using the colloidal synthesis method.We study their electronic structure as well as light absorption and emission processes.The photoluminescence spectra of the ZnO quantum dots exhibit obvious quantum confinement effect and sign of light reabsorption.We propose a material-independent model of light reabsorption,which explains well the experimental phenomenon.This model can be used to quantitatively study the light reabsorption of general semiconductor quantum dots.Through comparison of the size dependence of the ultraviolet and green luminescence peaks in conjunction with the theoretical calculation based on the effective mass approximation theory,we propose a luminescence mechanism of the ZnO quantum dots.Semiconductor–metal heteronanostructures have unique optical properties,but people know very little about their coupling properties at the interfaces.We study the coupling of the semiconductor exciton and metal surface plasmon polariton of the ZnO–Ag heteronanostructures.We fabricate the ZnO twin nanorod–Ag heteronanostructures by using the reduction of the silver ions.The relation between the crystallographic directions of ZnO and Ag is?0001?_ZnO//?111?_Ag.The absorption spectra show that the hybridized excitons have a splitting energy as high as 97 meV.In the luminescence spectrum,the hybridized-exciton peak shifts to red relative to the normal-exciton peak.We explain the experimental phenomenon by using the model of the exciton–surface plasmon polariton coupling.We fabricate the ZnO/ZnS core-shell nanostructures by using sulfuration of the ZnO quantum dots.The experiments show that the anion exchange induces the transformation of the ZnO quantum dots into the ZnO/ZnS core-shell nanostructures and ZnS quantum dots.We explain the quenching of the defect-associated luminescence of the ZnO quantum dots by using the charge transfer model.These results reveal that there is interaction between the components of the composite nanostructure.