Low-frequency Raman scattering of silver borate glasses

The vibrational dynamics of silver borate glasses has been investigated by Raman spectroscopy in the frequency region below 200 cm-1. The spectra show the presence of the boson peak (BP), whose shape and frequency location are almost independent of the silver concentration. The increase in the sound velocity with increasing silver ion content testifies to the progressive stiffening of the borate skeleton and refers to the existence of acoustic modes with increasing frequency. Consequently it is believed that the vibrational modes mainly contributing to the BP have a localized character and are decoupled from the acoustic phonons. An interpretation of these experimental observations ascribes a significant role in the evolution of the low-frequency vibrational dynamics of these glasses to the local vibrations of silver ions.