The preparation and optical properties of Ag and Ag/ZnO composite structure

Two-step fabrication technique was presented to prepare Ag/ZnO composite. Chemical reduction method was used to prepare Ag particles, and then nano-ZnO layer was deposited on the surface of Ag particles to form Ag/ZnO composites using wet chemical method. Hereafter, the structures, the morphologies, and the metal-enhanced fluorescence (MEF) properties of Ag particles and ZnO/Ag composites were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), Ultraviolet–visible spectroscopy, and fluorescence spectra (FL). From XRD patterns and TEM images, the results showed that Ag nanoparticles were successfully prepared, and Ag/ZnO composites also were obtained. Furthermore, the average diameter of Ag particles prepared for 18 min would decrease from 57 nm to around 40 nm after different nano-ZnO layers were deposited. This phenomenon could be explained by the growth mechanism of nano-ZnO layers, in which the chelation process between triethanolamine molecules and surface atoms of Ag particles was carried out to prevent the decrease in the average diameter of Ag particles. As the results of FL measurement, the MEF performance of Ag/ZnO composites firstly increased and then decreased with the increase in growth temperature of nano-ZnO layer. When nano-ZnO layers grew at 40 and 60 °C, the FL emission intensities of rhodamine 6G (R6G) molecules absorbing on different Ag/ZnO composites were larger than those of only R6G about 17.4 and 61.1 %, respectively. Moreover, the MEF property of Ag/ZnO composites would be attributed to the surface plasmon resonance of Ag particles and the change in photonic mode density and/or reduction in self-quenching of fluorophores, which might be due to nano-ZnO layer. Furthermore, when the Ag/ZnO composites were prepared for different time, the FL emission intensities of R6G molecules absorbing on different Ag/ZnO composites depended on the surface area of Ag/ZnO composites. But using different solvents, the FL emission intensities of R6G molecules absorbing on Ag/ZnO composites might be related to the agglomeration of R6G molecules.

In this paper, the Ag nanoparticles and the Ag/ZnO composite were prepared by two-step fabrication technique. The TEM images of the Ag/ZnO composites were given in below.