The shift of the optical absorption band edge of ZnO/ZnS core/shell nanotube arrays beyond quantum effects

Unlike conventional investigations that focus on the manipulation of optical absorption band edge for a single componential material through quantum confinement effects, in this paper, we study the optical absorption properties of well-ordered ZnO/ZnS core/shell nanotube arrays. Our data point out that the profile of the absorbance spectrum of ZnO/ZnS nanotube arrays is determined by the two components and geometrical parameters of the nanostructure arrays. We find that both of the ZnO and ZnS show a decrease in the optical band gap with the increase in ZnS thickness and the diameter of the nanotube arrays, which is interestingly out of explanation from the material aspect. The subsequent finite-difference-time-domain simulations support such observations and illustrate that the geometrical and periodical parameters could also impact the optical absorption of the core/shell nanostructure arrays, even without concerning the quantum effects.