FTIR SPECTROSCOPY TO MONITOR IMPURITIES AND IMPURITY-INTERACTIONS IN SILLENITE CRYSTALS

High resolution (0.04 cm(-1)) absorption spectroscopy is applied at 9 K to study the role played on the vibrational spectra by impurities (I m), as Si4+, Ge4+, P5+, V5+, Mn5+, and S6+, in Bi12SiO20 (BSO), Bi12Ge O20 (BGO), and Bi12TiO20 (BTO) sillenite single crystals, Up to three- phonon transitions (overtones of the F mode and combination of F and A modes) are detected for the impurities in ImO(4) tetrahedra. Weak anh armonicity effects are monitored. The presence of additional Im impuri ties modify the lines due to a) the stretching of OH, typical of the u ndoped material, and b) the multi-phonon transitions either of the int rinsic MeO4 (Me=Si, Ge, and Ti) and of the ImO(4) tetrahedra. New band s are monitored due to the Im-OH interaction.