The effect of mixed alkalis on EPR and optical bandgap in Fe3+ ions doped xLi2O-(30-x)Na2O-70B2O3 glasses

Chakradhar, Sreekanth RP and Yasoda, B and Rao, Lakshmana J and Gopal, NO (2004) The effect of mixed alkalis on EPR and optical bandgap in Fe3+ ions doped xLi2O-(30-x)Na2O-70B2O3 glasses. In: Asia-Pacific EPR/ESR Symposium 2004 (APES'04), 22-25, November 2004, Indian Institute of Scince, Bangalore-560 012, India, p. 112.

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Abstract

Electron Paramagnetic Resonance (EPR) and optical absorption studies of iron doped mixed alkali borate glasses, xLi2O-(30-x)Na2O-70B2O3-0.5Fe2O3 (5 \leq x \leq 28) have been investigated as a function of alkali content to look for the 'mixed alkali effect' (MAE) on the spectral properties of the glasses. The EPR spectra of all the investigated samples exhibit resonance signals which are characteristic of the Fe3+ ions. The EPR spectrum exhibits an intense resonance signal at g = 4.20 ± 0.1, a moderately intense signal at g = 2.00 ± 0.1 and a shoulder in the region of g = 7.60 ± 0.5. The existence of the resonances at g = 4.20 and g = 7.60 have been attributed to Fe3+ ions in rhombic and axial symmetry sites respectively. The g = 2.00 resonance is due Fe3+ ions coupled by exchange interactions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (\chi) have been evaluated. It is interesting to observe that N and \chi increase with x up to x = 20 and thereafter it decrease exhibiting a maximum at x = 20 showing the MAE effect. The EPR spectra have also been studied at different temperatures (123- 300 K). The number of spins participating in resonance is measured as a function of temperature and the activation energy is evaluated. It is observed that the temperature dependence of paramagnetic susceptibility (\chi) obeys Curie-Weiss law. From ultraviolet absorption edges, the optical bandgap and Urbach energies have been evaluated. It is interesting to observe that the optical band gap energy increases whereas the Urbach energy (\Delta E) decreases with x up to x = 25 showing the mixed alkali effect.

Item Type:	Conference Poster
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	21 Dec 2004
Last Modified:	19 Sep 2010 04:17
URI:	http://eprints.iisc.ac.in/id/eprint/2492

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