Optical properties and energy transfer processes in silver nanocomposite glasses

This thesis reports results on the spectroscopic properties and energy transfer processes in silver-doped aluminophosphate glasses. Material preparation was achieved by the melt-quenching technique, with tin being used for the chemical reduction of silver ions in order to promote Ag nanoparticles (NPs) formation upon heat treatment (HT). Absorption spectroscopy was used for the characterization of NPs based on surface plasmon resonance spectral features and for particle growth assessment. The nanocomposites have been also characterized by transmission electron microscopy and X-ray photoelectron spectroscopy, and results compared with those obtained from optical measurements.;Optical absorption and photoluminescence spectroscopy were used to study the optical properties of the material with two different concentrations of silver and tin: 4 and 8 mol. % of both Ag2O and SnO. For both concentrations, UV absorption measurements revealed features indicative of the occurrence of single Ag+ ions and twofold-coordinated Sn centers. For 8 mol. % Ag2O and SnO, the data also suggests the presence of Ag +-Ag+ and Ag+-Ag0 pairs. Interactions between nanoparticulate and ionic silver species are further studied for a glass with 4 mol. % Ag2O. For the first time, photoluminescence owing to plasmon resonance energy transfer (PRET) was observed which was interpreted as arising from an Ag NP → Ag+-Ag0 → Ag+-Ag+ energy transfer scheme. The spectroscopic properties of rare-earth ions in glasses containing silver and tin were also studied. An intensification of Eu3+ and Dy3+ ions emission was observed for excitation around 270 nm. Glass HT leads to a quenching effect on rare-earth ions luminescence ascribed to excitation energy transfer to Ag NPs. The effect of increasing the concentration of silver and tin on Dy3+ ions luminescence was assessed.;Relaxation dynamics of Ag NPs were studied by ultrafast pump-probe spectroscopy, namely by transient transmission and degenerate four-wave mixing measurements. An uncommon relaxation on the nanosecond time scale was observed for the glass with silver and tin which is assigned to energy transfer from polaronic and/or excitonic states in the near-interface region of the glass matrix to NPs. In contrast, a faster monotonic relaxation is observed for the nanocomposite with silver only which is consistent with PRET.