Influences of oxygen vacancies on the enhanced nonlinear optical properties of confined ZnO quantum dots

Confining ZnO quantum dots (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 N-2-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 N-2-annealed ZnO QDs is an instantaneous nonlinear process and is enhanced almost 2 times compared to that of O-2-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. (c) 2017 Elsevier B.V. All rights reserved.