Thermal Behavior of Silver in Ion-Exchanged Soda-Lime Glasses

The refractive index and the nonlinear optical properties of sodium silicate glass can be easily tailored by replacing the sodium with silver. However, the thermal responses of silver and the corresponding modifications of the silica (SiO2) network in ion-exchanged glass under heating are still not clear. X-ray photoelectron spectroscopy has been used to study the in-situ behavior of silver and SiO2networks on the surfaces of silver-ion-exchanged-content soda-lime glasses during heating and cooling processes under ultrahigh vacuum. Temperature-dependent concentration changes and oxidation states have been monitored. The results show that silver diffuses toward the surface, precipitates, and crystallizes during heating, and the total silver surface concentration is slowly increased during cooling. The concentration changes and binding-energy shifts of oxidized and neutral silver atoms, a new nonbridging oxygen species (NBO*), and a new silicon species (Si[a]) have been applied to deduce a disappropriation reaction mechanism of the Ag+ ion on the surface during annealing. The SiO2 network is modified at temperatures of <350°C to accommodate more silver on the surface and to balance the extra charge that is carried by the Ag+ ion. The fact that the SiO2 network polymerizes during annealing has been deduced from the results of the higher binding energies of Si 2p and O 1s after annealing. This observation is of importance in optimizing the distribution of the ion-exchanged silver and in the formation of silver-metal colloids in glass networks.