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EPR and optical investigations of manganese ions in alkali lead tetraborate glasses

Chakradhar, Sreekanth RP and Sivaramaiah, G and Rao, Lakshmana J and Gopal, NO (2005) EPR and optical investigations of manganese ions in alkali lead tetraborate glasses. In: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 62 (4-5). pp. 761-768. (In Press)

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Electron paramagnetic resonance (EPR) and optical absorption spectra of $Mn^{2+}$ ions in different alkali lead tetraborate glasses $90R_{2}B_{4}O_{7} + 9.25PbO + 0.75MnSO_{4}$ (R = Li, Na and K) and $90Li_{2}B_{4}O_{7} + (10-x)PbO + xMnSO_{4}$ (x = 0.1, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 and 2 mol%) have been studied. The EPR spectrum of all the glass samples exhibit three resonance signals at g = 2.0, 3.3 and 4.3. The resonance signal at g = 2.0 is attributed to the $Mn^{2+}$ ions in an environment close to an octahedral symmetry. The resonance signals at g = 3.3 and 4.3 have been attributed to the rhombic symmetry of the $Mn^{2+}$ ions. The effect of temperature (123-433 K) and the composition dependence of EPR signals have been studied for $Mn^{2+}$ ions in lithium lead tetraborate glasses. It is interesting to observe that the variation of paramagnetic susceptibility (\chi) with temperature obeys Curie-Weiss law. From the slope of 1/\chi versus T graph, the Curie constant (C) has been evaluated. The zero-field splitting (zfs) parameter D has been calculated for different alkali lead tetraborate glasses from the intensities of the allowed hyperfine lines. The optical absorption spectrum exhibits three bands. An intense and broad band at lower energy side has been assigned to the spin-allowed $(^{5}E_{g}-^{5}T_{2g})$ transition of $Mn^{2+}$ ions in an octahedral symmetry. The intense and sharp band and a broad band at higher energy side have been assigned to charge transfer bands. A red shift is observed with increase of alkali ion size. The optical band gap energy $(E_{opt})$ decreases, whereas the Urbach energies (\Delta E) increases with increase of Mn content. The theoretical values of optical basicity (\Delta th) of the glasses have also been evaluated.

Item Type: Journal Article
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Additional Information: Copyright for this article belongs to Elsevier.
Keywords: Mn2+ ions;Alkali lead tetraborate glasses;EPR;Optical absorption
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 01 May 2006
Last Modified: 19 Sep 2010 04:20
URI: http://eprints.iisc.ernet.in/id/eprint/3653

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