Structural and Optical Properties of Silver-Doped Zirconia and Mixed Zirconia−Silica Matrices Obtained by Sol−Gel Processing

The annealing behavior of zirconia and mixed zirconia−silica matrices (with different ZrO 2 /SiO 2 molar ratios) containing silver nanoclusters, synthesized by the sol−gel technique has been investigated. The film samples of the general formula (SiO 2 ) x (ZrO 2 ) (0.9 - x ) Ag 0.1 ( x = 0, 0.225, 0.45, 0.675, and 0.9) were treated in different atmospheres (air, N 2, and 5%H 2 −95%N 2 ) at temperatures ranging from 200 to 900 °C. The ZrO 2 matrix undergoes a structural phase transition from amorphous to cubic-tetragonal polycrystalline between 400 and 500 °C and on further raising the temperature near 600−700 °C the monoclinic phase also develops. On the contrary, the ZrO 2:SiO 2 system remains amorphous up to ∼700 °C. Ag nanoclusters are formed in all the systems. It has been observed that the change in the ZrO 2 /SiO 2 molar ratio is an effective way to control not only the overall refractive index of the matrix but also the Ag cluster size. The shifting of the surface plasma resonance position of Ag nanoclusters is observed as a function of the refractive indices of the matrix following the Mie theory. Samples where characterized by transmission electron microscopy, Rutherford backscattering spectrometry, and optical spectrometry to correlate the cluster structure to their optical properties.