Optical absorption spectra of Mn3+ ions in vesuvianites from Lower Silesia, Poland

Lilac, yellow and pink, small crystals of manganese-bearing (up to 1.10 wt.%) vesuvianites from Lower Silesia, Poland, were studied by optical and IR spectroscopic methods. Absorption spectra of the lilac sample show an intense, broad band at 18500 cm(-1) in the E perpendicular to c-polarization and weak bands at 23100 cm(-1) 18500 cm(-1) and 12500 cm(-1) in the E parallel to c-polarization. The spectra of the yellow vesuvianites have a strong E perpendicular to c-polarized band near 23600 cm(-1) and weak bands at 23900 cm(-1), 22700 cm(-1) and 20100 cm(-1) in the E parallel to c-polarization. The spectra of the pink variety result from superposition of Mn3+-bands in the spectra of the lilac and yellow vesuvianites. It has been concluded that spectra of the yellow vesuvianite studied are due to Mn3+ ions occupying the fivefold-coordinated B-sites (C-4v symmetry). The dominating absorption band 23600 cm(-1) is assigned to the only symmetry-allowed transitions B-5(1) --> (5)E in Mn3+ ions. The spectra of the lilac variety can be assigned to Mn3+ ions in the distorted AlFe-octahedra or also in B-sites, which have different B-O-10 distances. The distribution of Mn3+ in nan-equivalent structural positions of the vesuvianites studied may be the result of different temperatures of crystallization and of the state of ordering, which is supported by IR spectroscopic investigations.