Optical properties of exciton confinement in spherical ZnO quantum dots embedded in SiO2 matrix

The optical characteristics of ZnO nanoparticles in SiO2 matrix have been determined by UV-visible and photoluminescence (PL) studies. The PL spectrum of the ZnO quantum dots shows two different bands: the first one is a broad green emission band related to deep level emission in the visible range and the second one is situated at 3.48 eV in the ultraviolet region, and is attributed to the recombination of electrons in the conduction band and holes in the valence band. The experimental result that we found was simulated numerically using different methods. Our calculations revealed a good agreement between the matrix element calculation method and the experimental result. We have also calculated the ground state binding energy, the oscillator strength and the radiative lifetime of the exciton in a ZnO spherical quantum dot. It was clearly shown from our calculation that these physical parameters are very sensitive to the quantum dot size. As a consequence, the optical and electronic properties of the dot can be controlled and also tuned through the nanoparticle size variation. These results could be particularly helpful, since they are closely related to experiments performed on such nanoparticles; this may allow us to improve the stability and efficiency of semiconductor quantum dot luminescence, which is considered critical. (C) 2009 Elsevier Ltd. All rights reserved.