Silicon as Reducing Agent for Controlled Production of Plasmonic Copper Nanocomposite Glasses: A Spectroscopic Study

The use of silicon to produce metal nanocomposite phosphate glasses with plasmonic properties is proposed. It is demonstrated how the reducing properties of Si powder allow for producing Cu nanocomposite glasses in a controlled manner during heat treatment (HT). Cu/Si-codoped glasses were prepared in a 50BaO–50P₂O₅ matrix by a simple melt-quench method in ambient atmosphere. The worst-case scenario is considered by having the noble metal introduced in its higher oxidation state as copper(II) oxide, i.e., instead of using monovalent copper. Optical absorption and photoluminescence (PL) spectroscopy, including emission decay dynamics, were employed for characterization of the melt-quenched glass, and for investigating the influence of HT on material optical properties. Remarkably, increasing amounts of Si powder were observed to suppress and ultimately remove the Cu²⁺ visible absorption band in the CuO-containing glasses. Moreover, subsequent HT of the glass with the highest Si content resulted in progressive development of the surface plasmon resonance of Cu nanoparticles with increasing holding time. PL spectroscopy analysis is further employed towards elucidating the Cu²⁺ → Cu⁺ → Cu⁰ valence state changes likely occurring during the melting and subsequent thermal processing.