FT -IR Spectroscopy of Tetrahedrally Coordinated Impurities in Sillenites

FT-IR absorption spectroscopy in the temperature range 9-300 K was used to study the vibrational modes induced by aliovalent impurities (such as ps+ and V 5 +) in Bi 12Si020(BSO), Bi 12Ge020(BGO), and Bi 12Ti020(BTO) and by traces ofGe4+ in Bi 12Si020 and of Si 4 + in Bi 12 Ti020. Peaks due to the asymmetric F stretching mode, to its overtone, and to the combination with the symmetric A mode of the tetrahedral Im04 unit (Im being the impurity) were detected. Weak anharmonicity effects were displayed. The roJe played by the host matrix and by temperature on the peak positions was examined and discussed.