An interpretation of the Boson peak in rare-earth ion doped glasses

The Boson peak in the Raman spectra of glasses is an ubiquitous feature. We show that doping a series of fluoride, tellurite and sulfide glass composi tions with rare-earth ions, such as Pr3+, Dy3+, Nd3+, Ce3+, at concentratio ns between 1000 and 10,000 ppm, increases the amplitude of the Boson peak a s compared to the respective undoped glasses. Further addition of rare-eart h ions results in saturation and even reduction of the Boson peak ascribed to clustering of dopants and/or devitrification of glass host. Prolonged ir radiation of photorefractive sulfide glasses with near-bandgap laser light also results in an increase of the Boson peak. A model is suggested for cha nges in the intensity and position of the Boson peak with glass composition , doping level, and after prolonged irradiation of photorefractive glasses. We propose that the presence of non-bridging anion atoms, such as F, O or S, (or anion atoms having strained bonds with increased polarizability), de termines the Boson peak, as well as the solubility of rare-earth ions in gl asses. (C) 1999 Elsevier Science B.V. All rights reserved.