Raman spectroscopic analysis on the solubility mechanism of La3+ in GeS2-Ca2S3 glasses

In comparison to other chalcogenide glasses, Ge-Ga-S glasses have the largest rare-earth solubility. Raman spectra of GeS2-Ga2S3 glasses contain two bands at 265 and 385 cm(-1) which increased in intensity with the addition of Ga2S3. These are associated with the vibration of Ge-Ge bonds and edge-shared GaS4 tetrahedra, respectively. Upon the addition of La2S3 into GeS2-Ga2S3 glasses, intensities of these two bands decreased while a new band appeared at 375 cm(-1) due to the vibration of tetrahedra with non-bridging sulfur(s). Dissociation of Ge-Ge bonds and edge-shared GaS4 tetrahedra through the addition of La2S3 are responsible for the non-bridging sulfur formation. La3+ can be dissolved into the glass network as charge compensators for these non-bridging sulfurs. Since no such structural unit is present in glasses without Ga2S3, this connection scheme and the structural modification in Ga-containing chalcogenide glasses seem to be crucial for an increase of La3+ solubility. (C) 1998 Elsevier Science B.V. All rights reserved.