Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing CuO – An EPR and optical study

Abstract

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of 0.5 mol% CuO doped xLi 2 O-(30 À x)Na 2 O-69.5B 2 O 3 (5 6 x 6 25) mixed alkali glasses have been investigated. The EPR spectra of all the investigated samples exhibit resonance signals characteristic of Cu 2+ ions in octahedral sites with tetragonal distortion. It is found that the spin-Hamiltonian parameters do not vary much with x. It is interesting to observe that the number of Cu 2+ ions participating in resonance (N) and its paramagnetic susceptibility (v) exhibits the mixed alkali effect with composition. It is observed that the temperature dependence of paramagnetic susceptibility (v) obeys Curie-Weiss law. The paramagnetic Curie temperature (h p ) is negative for the investigated sample, which suggests that the copper ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. A broad band corresponding to the transition 2 B 1g ! 2 B 2g in the optical absorption spectrum shows a blue shift with x. By correlating the EPR and optical absorption data, the molecular orbital coefficients a 2 and b 2 1 have been evaluated. It is interesting to observe that the optical band gap (E opt ) and Urbach energies (DE) exhibit the mixed alkali effect. The theoretical values of optical basicity (K th ) have also been evaluated.

Laser patterning of oriented LiNbO3 crystal particle arrays in NiO‐doped lithium niobium silicate glasses

“…Further studies on the coordination state of Ni 2+ ions in LNS glass are desired. In CuO‐doped LNS glasses showing green color, strong and broad absorption peaks are observed at the center of 750‐800 nm, which are assigned to the 2 B 1g → 2 B 2g transition in Cu 2+ ions in octahedral sites with strong tetragonal distortions . Furthermore, it is observed that the absorption edge shifts toward longer wavelength due to the addition of CuO.…”

Investigations of the local distortions and EPR parameters for Cu2+ in xNa2O‐(30–x)K2O‐70B2O3 (5 ≤ x ≤ 25 mol%) glasses

“…This point is also supported by the similar large relative tetragonal elongation ratios (~16%) for Cu 2+ in analogous mixed alkali borate xLi 2 O·(30–x)·Na 2 O·69.5B 2 O 3 (5 ≤ x ≤ 25 mol%) glasses. Meanwhile, the large relative tetragonal elongations for divalent copper in both mixed alkali borate glasses are associated with low g ⊥ (~2.04) due to the large magnitude of negative Ds and the energy denominator E 2 . It appears that the local distortions in glass systems can be effectively revealed by paramagnetic Cu 2+ probes with the aid of EPR analysis. For Cu 2+ in NKB glasses, the experimental d‐d transition bands and EPR parameters exhibit distinct variation rules with the composition of Na 2 O.…”

Formation and its mechanism of copper metal layers at surface by annealing in reduced atmosphere in CuO–Li2O–Nb2O5–SiO2 glass

“…On the other hand, the CuO-doped glass shows the absorption edge at~500 nm and a broad and asymmetrical peak centered at~750 nm. It is known that Cu 2+ ions with the electronic configuration of 3d 9 in glass give a strong and broad absorption peak at~800 nm, and its peak is assigned to the 2 B 1g → 2 B 2g transition in Cu 2+ ions in octahedral sites with strong tetragonal distortions [24,25]. That is, the broad and asymmetrical peak centered at~750 nm shown in Fig.…”