Enhanced boson peak in Pr-doped Ge-S-I glasses with varying composition and Pr-content

Raman scattering from Ge-rich, undoped and Pr-doped Ge-S-I glasses is reported over the spectral range 5-450 cm(-1). In the region of molecular vibrations, apart from the bands of the Ge-S binary glassy system, an additional band at 222 cm(-1) has been observed and assigned to I vibrations in terminating Ge-I bonds. A well-resolved, strong Boson peak has also been observed at similar to 26 cm(-1) in all samples, the intensity of which increases with increasing I-content. The strength of this peak is associated with the large atomic mass and polarizability of I, and its frequency is connected with the medium range order of the glass. Doping with Pr3+ results in further enhancement of the Boson peak, indicating that Pr ions are incorporated mainly into regions of the glass responsible for the collective modes producing this peak. Measured lineshape characteristics on both sides of the Boson peak are in satisfactory agreement with the predicted ones by the soft potential model [Gurevich ed al., Phys. Rev., B48, 1993, 16318]. (C) 1998 Elsevier Science Ltd. All rights reserved.