The mixed alkali borate glasses xNa 2 O-(30 − x)K 2 O-70B 2 O 3 (5 x 25), doped with 0.5 mol% of CuO, have been investigated, using electron paramagnetic resonance (EPR) and optical absorption techniques, as a function of mixed 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 Cu 2+ ions in octahedral sites with tetragonal distortion. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. It is observed that the spin-Hamiltonian parameter g goes through a minimum around x = 10-15 whereas A goes through a maximum around x = 15 showing the MAE. The number of spins participating in resonance (N 2 ) and the calculated paramagnetic susceptibilities (χ) exhibit a shallow minimum around x = 20 showing the MAE in these glasses. The optical absorption spectrum of the x = 5 glass exhibits two bands: a strong band centred at 14 240 cm −1 corresponding to the transition ( 2 B 1g → 2 B 2g ) and a weak band on the higher energy side at 22 115 cm −1 corresponding to the transition ( 2 B 1g → 2 E g ). With x > 5, the higher energy band disappears and the lower energy band shifts slightly to the lower energy side. By correlating the EPR and optical absorption data, the molecular orbital coefficients α 2 and β 2 1 are evaluated for the different glasses investigated. The values indicate that the in-plane σ bonding is moderately covalent while the in-plane π bonding is significantly ionic in nature; these exhibit a minimum with x = 15, showing the MAE. The theoretical values of optical basicity of the glasses have also been evaluated. From optical absorption edges, the optical bandgap energies have been calculated and are found to lie in the range 3.00-3.40 eV. The physical properties of the glasses studied have also been evaluated with respect to the composition. Table 1. Composition of glasses (mol%) studied in the present work. Glass code, x Glass system 5 5 N a 2 O-25K 2 O-69.5B 2 O 3 -0.5CuO 10 10Na 2 O-20K 2 O-69.5B 2 O 3 -0.5CuO 15 15Na 2 O-15K 2 O-69.5B 2 O 3 -0.5CuO 20 20Na 2 O-10K 2 O-69.5B 2 O 3 -0.5CuO 25 25Na 2 O-5K 2 O-69.5B 2 O 3 -0.5CuO
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.