In situ growth of luminescent silver nanoclusters inside bulk sol-gel silica glasses

Silver nanocluster-doped glasses are attractive materials for various photonic applications. In this paper, bulk silica glasses doped with luminescent silver nanoclusters have been prepared using the sol-gel technique. As a first step, dense silica glasses doped with ionic silver have been loaded with hydrogen. Thereafter, a heat-treatment in air atmosphere was performed to enable the growth of silver nanoclusters at different temperatures in the range 100-600 degrees C. The optical properties of the obtained nanocomposites have been studied, as a function of the post-annealing temperature, using optical absorption and photoluminescence spectroscopies. It has been shown that, under UV photoexcitation, the hydrogenated samples, heat-treated between 200 and 500 degrees C present visible luminescence due to cationic and neutral molecular-like silver clusters, consisting of a small number of Ag atoms or ions. After annealing at 600 degrees C, further Ag aggregation led to 2 nm-size silver nanoparticles, resulting in a quenching of the visible luminescence.