Influences Of Oxygen Vacancies On The Enhanced Nonlinear Optical Properties Of Confined ZnO Quantum Dots

In recent years,with the development of the times and the progress of science and technology,quantum dot semiconductor materials have become the object of extensive research in nanomaterials.Semiconductor quantum dot materials have quantum confinement effects,and many unique optoelectronic properties.ZnO has emerged as a promising optoelectronic material due to its large exciton binding energy of 60 m eV,and direct wide band gap of 3.3 eV.The properties of a single quantum dot is relatively limited,but the composite quantum dot can produce many new properties that cannot be obtained with a single quantum dot.The structure,physical and chemical states of the composite quantum dot are stable,and the practical value of the composite quantum dot can be realized in the device.ZnO quantum dots confined in Al₂O₃ matrix were fabricated using pulsed laser deposition?PLD?method and rapid thermal annealing?RTA?technique.We characterized the embedded ZnO quantum dots?QDs?using transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?and Raman spectroscopy?Raman?.Magnetic and nonlinear optics of confined ZnO QDs were studied with the help of a physical property measurement system?PPMS?,Z-scan,and pump-probe.We investigated the effect of oxygen vacancies on the nonlinear optical properties of confined ZnO QDs.The contents of this thesis are as following:Confining ZnO QDs into a solid state matrix to form nanocomposite materials is an important mean to design nonlinear optical devices.In this paper,ZnO confined in Al₂O₃ matrix are synthesized by pulsed laser deposition method and rapid thermal annealing technique.The substantial oxygen vacancies are generated in the N₂-annealed ZnO QDs.Magnetic measurements illustrate that the ferromagnetic nature of ZnO QDs confined in Al₂O₃ matrix can be due to the oxygen vacancies.The determined two-photon absorption in N₂-annealed ZnO QDs is an instantaneous nonlinear process and is enhanced almost 2 times compared to that of O₂-annealed ZnO QDs.The enhancement of optical nonlinearities achieved in confined ZnO QDs with substantial oxygen vacancies is important for the practical applications of ZnO nanostructures in such as optical limiting devices and all-optical switching elements.