VIBRATIONAL PROPERTIES OF RARE-EARTH PHOSPHATE-GLASSES

The Raman spectra of metaphosphate glasses, which contain very high concentrations of either Eu3+ Or Gd3+ ions, have been measured over a wide range of temperatures (10-300 K). The high-frequency part of the spectrum (above 200 cm(-1)) is similar to that found for other phosphate glasses, indicating that these glasses share the common structural feature of a skeleton built up from (PO4)(2-) tetrahedral units. The low-frequency region is determined by two spectral contributions which are 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 with increasing temperature, while the latter does not change appreciably as the temperature is increased to room temperature. Interpretation of the light scattering excess and the boson peak in terms of the predictions of the soft potential model can account for their frequency and temperature dependences.