EPR and optical studies of Mn2+ ions in Li2O-Na2O-B2O3 glasses - An evidence of mixed alkali effect

摘要

EPR and optical absorption spectra of 0.5 mol% MnO2 doped xLi(2)O-(30 - x)Na2O-69.5B(2)O(3) (5 <= x <= 25) glasses have been studied. The EPR spectra exhibit resonance signals characteristic of Mn2+ ions. The resonance signal at g congruent to 2.0 is due to Mn2+ ions in an environment close to octahedral symmetry, whereas the resonances at g congruent to 4.3 and g congruent to 3.3 are attributed to the rhombic surroundings of the Mn2+ ions. The ionic character (A), the number of spins participating in resonance (N), optical band gap energies (E-opt) and Urbach energies (Delta Epsilon) show the mixed alkali effect (MAE) with composition. The present study gives an indication that the size of alkalis we choose, is also an important contributing factor in showing the MAE. The variation of N with temperature obeys the Boltzmann law. The optical absorption spectra show a single broad band at similar to 21000 cm(-1) corresponding to the transition 6A(1g)(S) -> T-4(1g)(G) which exhibits a blue shift with x. The theoretical values of optical basicity (A(th)) have also been evaluated. (C) 2007 Elsevier B.V. All rights reserved.