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 (Im), as Si4+, Ge4+, P5+, V5+, Mn5+, and S6+, in Bi12SiO20 (BSO), Bi12GeO20 (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 anharmonicity effects are monitored. The presence of additional Im impurities modify the lines due to a) the stretching of OH, typical of the undoped material, and b) the multi-phonon transitions either of the intrinsic MeO4 (Me=Si, Ge, and Ti) and of the ImO(4) tetrahedra. New bands are monitored due to the Im-OH interaction.