EPR and optical absorption studies of Cr3+ ions in alkaline earth alumino borate glasses

摘要

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cr3+ ions in Calcium alumino borate (CaAB) glasses have been studied. The EPR spectra exhibit weak resonance signal at g approximate to 4.50 and intense resonance signal at g approximate to 1.98. A sharp resonance signal at g approximate to 1.97 was also observed at lower concentrations of chromium. The concentration dependence of the linewidth of the resonance signal at g approximate to 1.98 suggests the formation of Cr3+ ion clusters by magnetic superexchange interactions. The temperature dependence of the peak to peak intensity and the linewidth of the resonance signal at g approximate to 1.98 suggests that the exchange interactions between Cr3+ ions in the present sample were antiferromagnetic in nature with Neel temperature, T-N = 233 K. From the number of spins participating in the resonance at g approximate to 1.98, the paramagnetic susceptibility (chi) was calculated at different temperatures (233-295 K). A plot of 1/chi and T was found to obey Curie-Weiss law with negative Curie temperature. By measuring the relative intensities of the resonance signal at g approximate to 1.98, at different temperatures, the value of antiferromagnetic coupling constant (J) has been estimated. The optical absorption spectrum of chromium doped CaAB glass exhibits four bands, characteristic of Cr3+ ions, in nearly octahedral symmetry. From the band positions, the crystal field splitting parameter, Dq and the Racah interelectronic repulsion parameters, B and C were evaluated. The optical band gap (E-opt) and the Urbach energy (Delta E) were calculated from the ultraviolet absorption edges. (c) 2006 Springer Science + Business Media, Inc.