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 compositions with rare-earth ions, such as Pr3+, Dy3+, Nd3+, Ce3+, at concentrations between 1000 and 10,000 ppm, increases the amplitude of the Boson peak as compared to the respective undoped glasses. Further addition of rare-earth ions results in saturation and even reduction of the Boson peak ascribed to clustering of dopants and/or devitrification of glass host. Prolonged irradiation of photorefractive sulfide glasses with near-bandgap laser light also results in an increase of the Boson peak. A model is suggested for changes 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), determines the Boson peak, as well as the solubility of rare-earth ions in glasses. (C) 1999 Elsevier Science B.V. All rights reserved.