VIBRATIONAL PROPERTIES OF RARE-EARTH PHOSPHATE-GLASSES

The Raman spectra of metaphosphate glasses, which contain very high co ncentrations of either Eu3+ Or Gd3+ ions, have been measured over a wi de range of temperatures (10-300 K). The high-frequency part of the sp ectrum (above 200 cm(-1)) is similar to that found for other phosphate glasses, indicating that these glasses share the common structural fe ature of a skeleton built up from (PO4)(2-) tetrahedral units. The low -frequency region is determined by two spectral contributions which ar e characteristic of the disordered topology of vitreous materials: the tight-scattering excess and the 'boson peak'. The former contribution , clearly observed for frequencies below 10 cm(-1), becomes larger wit h increasing temperature, while the latter does not change appreciably as the temperature is increased to room temperature. Interpretation o f the light scattering excess and the boson peak in terms of the predi ctions of the soft potential model can account for their frequency and temperature dependences.