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 (1m), as Si 4+ , Ge 4+ , P 5+ , V 5+ , Mn 5+ , and 5 6+ , in Bi 12 SiO 20 (BSO), Bi 12 GeO 20 (BGO), and Bi 12 TiO 12 (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 lm 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 MeO 4 (Me=Si, Ge, and Ti) and of the ImO 4 tetrahedra. New bands are monitored due to the Im-OH interaction.