The effect of mixed alkali on EPR and optical absorption spectra in mixed alkali borate xNa2O–(30−x)K2O–70B2O3 glasses doped with iron ions

Abstract

Electron paramagnetic resonance (EPR) and optical absorption studies of iron doped mixed alkali borate glasses, xNa 2 O-(30 À x)K 2 O-70B 2 O 3 (5 6 x 6 25) have been investigated as a function of alkali content to look for the Ômixed alkali effectÕ on the spectral properties of the glasses. The EPR spectra of all the investigated samples exhibit resonance signals which are characteristic of the Fe 3+ ions. The EPR spectrum exhibits an intense resonance signal at g = 4.02 ± 0.1, a moderately intense signal at g = 2.02 ± 0.1 and a shoulder in the region of g = 7.20 ± 0.5. The existence of the resonances at g = 4.02 and g = 7.20 have been attributed to Fe 3+ ions in rhombic and axial symmetry sites respectively. The g = 2.02 resonance is due to Fe 3+ ions coupled by exchange interactions. The number of spins (N) participating in resonance and its paramagnetic susceptibility (v) have been evaluated. It is observed that N and v decrease with x up to x = 10 and then increase up to x = 15 exhibiting a minimum at x = 10 and a maximum at x = 15 and thereafter it gradually decreases. The optical absorption spectrum exhibits three bands assigned to 6 A 1g (S) ! 4 A 1g (G), 4 E g (G); 6 A 1g (S) ! 4 T 2g (G) of Fe 3+ and the other band is assigned to Fe 2+ -Fe 3+ inter-valence charge transfer band. From ultraviolet absorption edges, the optical bandgap and Urbach energies have been evaluated. The optical band gap energy obtained in the present work varies 2.74-3.77 eV for both the direct and indirect transitions. The physical parameters of all the glasses have been evaluated with respect to x.

Optical and FTIR studies of CuO-doped lead borate glasses and effect of gamma irradiation

“…The observed UV bands at 220-230, 275-285, 310 nm in various glasses have been attributed to Fe 3 + ions usually present in tetrahedral condition by most authors [30,31]. However, recent studies [32][33][34] have revealed that the Fe 3 + ions can also be present in octahedral sites. This controversy needs still further work to specify the exact coordination of the trace iron impurity present.…”

Absorption Studies on Some Silicate and Cabal Glasses Containing NiO or Fe2O3or Mixed NiOi + Fe2O3

“…Although studies on iron in glass have attracted the attention of the majority of scientists interested in transition metal behavior in various glasses, yet much recent work by Sreekanth Chakradhar et al [16,17] have postulated that Fe 3+ ions exhibit an octahedral symmetry in contradiction with most previous published works. It is (471) evident, therefore, that further studies are still needed by different recent techniques to justify the exact coordination of both iron states in various glasses.…”

“…The majority of Fe ions are believed by many authors to occupy tetrahedral network-forming sites in silicate glasses [10,11,14], although this has been disputed. Conversely, the majority of Fe 2+ ions are thought to occupy octahedral network--modifying sites [15][16][17].…”

EPR and optical absorption studies of Fe3+ ions in sodium borophosphate glasses

“…The EPR spectrum of transition metal ions in phosphate glasses is an interesting research subject and affords a method to investigate the glass structure. EPR spectra of Fe 3 + ions in various glasses have been extensively studied [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. It is reported that the trivalent iron ions can take two different coordination sites, i.e., either tetrahedral or octahedral sites in glasses.…”