Spectroscopic study of manganese-containing borate and borosilicate glasses: cluster formation and phase separation
The coordination and bonding of Mn2+ ions in glasses can be probed sensitively and selectively by electron paramagnetic resonance (EPR) and photoluminescence spectroscopy. These methods also give information on Mn–Mn ion interactions and cluster formation. Mn2+ ions were found to be tetrahedrally coordinated in borosilicate glasses of high optical basicity, and octahedrally coordinated in low alkaline borosilicate glasses (Duran-type) as well as in binary borate glasses. Broad emission bands and multicomponent fluorescence decay curves in Duran glasses indicate very strong Mn–Mn ion interactions and the presence of multiple Mn2+ sites, even at low Mn-levels. The EPR spectra show exchange narrowing with increasing Mn content in the Duran series, which is caused by a decrease in the Mn–Mn distances as edge sharing MnO6 octahedra are formed. The network structure of Mn-containing binary and ternary borate glasses is discussed on the basis of their infrared spectra. Addition of MnO to Duran glasses is found to cause the preferential transformation of [BO3]0 to [BO4]– groups, and to a lesser extent of silicate Q4 to Q3 units. An increase of the relative population of homopolar B–O–B or Si–O–Si bonds, with the simultaneous decrease in the number of mixed B–O–Si bonds, is also observed, and this explains the visible phase separation of Duran glasses when MnO is added in excess of 4 mol%.
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Document Type: Research Article
Publication date: February 1, 2013