Er photoluminescence enhancement in Ag-doped sol–gel planar waveguides

This paper reports on the study of the effects of silver (Ago) nanoparticles on the optical and spectroscopic properties of Er3+-doped silica-based gels and glasses, including active bulk materials and planar waveguides for integrated optics. Two different procedures for silver and erbium ion incorporation into the glassy matrices have been investigated: the direct incorporation of a metal salt (AgNO3 and/or Er(NO3)3) into the sol–gel solution, as well as a modified sol–gel process, based on pore-doping of a precursor gel with AgNO3 and/or Er(NO3)3 solutions. The study of the parameters determining the average size and size distribution of the nanoparticles, together with their influence on the sol–gel material densification and Er3+ photoluminescence at 1.5 μm, has been performed by means of transmission electron microscopy, plus ultra-violet/visible and photoluminescence spectroscopies. The Ago colloidal nanoparticles, obtained by thermal precipitation, were approximately spherical, homogeneously distributed and they exhibited an average size between ∼2 and 15 nm, depending on the silver content and heat treatment performed. They are shown to be responsible for a remarkable enhancement of the Er3+ photoluminescence intensity, which is mainly due to the increase of the local electric field around the Er3+ ions, due to the surface plasmon resonance of the Ago nanoparticles.