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Chromium ions in alkali lead borotellurite glasses-An EPR and optical study

Chakradhar, Sreekanth RP and Rao, Lakshmana J and Sivaramaiah, G and Gopal, NO (2005) Chromium ions in alkali lead borotellurite glasses-An EPR and optical study. In: physica status solidi (b), 242 (14). pp. 2919-2929.

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Abstract

Chromium ions doped $90 Na_{2}B_{4}O_{7} + (9-x)PbO + 1TeO_{2}$ and $90 K_{2}B_{4}O_{7} + (9-x)PbO + 1TeO_{2}$ (x = 3, 4, 5, 6, 7 and 8 mol%) glasses have been studied by using Electron Paramagnetic Resonance (EPR) and optical absorption techniques. The EPR spectra exhibit a broad resonance signal at g = 4.65 and a narrow resonance signal at g = 1.97. The resonance at g = 4.65 can be attributed to isolated $Cr^{3+}$ ions in rhombic symmetry subjected to strong crystal field effects and the resonance at g = 1.97 is due to $Cr^{5+}$ ions. The EPR spectra have also been studied at different temperatures (153-393 K). The number of spins (N) participating in the resonance is measured as a function of temperature and the activation energy is calculated. The exchange coupling constant J between chromium ions is calculated. The optical absorption spectrum exhibits bands characteristic of Cr3+ ions in an octahedral symmetry. The optical band gap $(E_{opt})$ and Urbach energies (\Delta E) have been calculated for all the glass samples and it is observed that $E_{opt}$ decreases and \Delta E increases with increase of chromium content. This has been explained as due to the creation of additional localized states with chromium doping, which overlap and extend in the mobility gap of the glass matrix.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to Wiley-VCH Verlag GMBH.
Keywords: Chromium ions.alkali lead borotellurite glasses;EPR;optical study
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 26 Oct 2005
Last Modified: 19 Sep 2010 04:20
URI: http://eprints.iisc.ernet.in/id/eprint/3881

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