RAMAN STRUCTURAL INVESTIGATION OF MANGANESE DOPED 
BORO-TELLURITE GLASSES

D. Maniu, T. Iliescu, I. Ardelean, S. Astilean

Faculty of Physics, Babes Bolyai University, Kogalniceanu 1, 400084, Cluj-Napoca, Romania

	Glasses having the compositions xMnO·(1-x)[70TeO2·25B2O3·5SrO] with 0 ≤ x ≤ 0.5 were studied by means of Raman spectroscopy. 
Non-crystalline solid tellurite glasses continue to intrigue both academic and industry researchers not only because of their many technical applications, but also because of a fundamental interest in understanding their microscopic mechanisms. Tellurite glasses present scientific importance due to their pronounced nonlinear optical properties as well to their potential as a appropriate material for fiber amplifier. Furthermore, tellurite glasses have high refractive indices in the range from 1.85 to 2.2 and show good infrared transmittance. Raman spectroscopy is an effective tool for resolving the structure of local arrangements in glasses. Raman spectra are particularly well suited for studying boro tellurite glasses because peaks in the region of 600 to 800 cm–1 are generally attributed only to tellurite and not to the borate species which, by comparison, scatter weakly. The influence of a gradual addition of the modifier manganese oxide on the glass structure has been elucidated.
	The Raman spectra of xMnO·(1-x)[70TeO2·25B2O3·5SrO] with 0 ≤ x ≤ 0.5 are characterized by three bands, located around 470 cm-1, 670 cm-1, and 770 cm-1. 
The 470 cm-1 and 670 cm-1 have been assigned to the symmetric and antisymmetric vibration of Te-O-Te bonds in TeO4 trigonal bipyramids and the 770 cm-1 was attributed to the stretching vibration between tellurium and nonbridging oxygen atoms from TeO3 trigonal pyramids. 
The Raman spectra of the studied glasses change significantly with the modification of MnO content. 
At lower content of manganese oxide (x ≤ 0.1) the TeO4 units dominate in the glass network. In Raman spectra of these glasses, a week shoulder appears at ~ 800 cm-1 due to boroxol ring oxigen breathing, involving a very little boron motion.
At high content of manganese oxide (x > 0.1) the glass network is predominant by TeO3 units. The ratio of TeO4/TeO3 structural units changes with the modifier addition. 
Therefore, the addition of manganese oxide determines the transformation of TeO4 trigonal bipyramides in TeO3 trigonal pyramids. The gradual addition of the MnO on the glass structure involves a change in the coordination number of tellurite atoms from 4 to 3.

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