Compositional Profiles in Silica-Based Sol-Gel Films Doped with Erbium and Silver, by RBS and ERDA

Abstract

The photoluminescence efficiency of Er-doped silica-titania planar waveguides, prepared by sol-gel processing, may in principle be enhanced through the incorporation of silver metal particles. On the other hand, the presence of residual OH groups limits the optical activity of the Er³⁺ ions. In this work, we have used Rutherford Backscattering Spectrometry (RBS), combined with Elastic Recoil Detection Analysis (ERDA), in order to study the incorporation of Ag and H species as a function of the heat treatments used to densify the sol-gel films. Ultraviolet–visible spectroscopy and Fourier transform infrared (FTIR) spectroscopy were used to support and expand the interpretation of the RBS and ERDA data. The RBS results indicate a homogeneous distribution of Er in the as-deposited films. On the contrary, Ag displays a bimodal in-depth profile, centred at the air/film and film/Si substrate interfaces. Heat treatments at up to 700°C eventually lead to in-diffusion and segregation of most of the Ag species at the latter interface. The hydrogen concentration reaches minimum values after heat treatments at 500 and 900°C, with apparently larger values for temperatures in between. During these heat treatments, the Er profile remains stable.