Electron paramagnetic resonance, optical absorption and photoluminescence properties of Cu2+ ions in ZnO-Bi2O3-B2O3 glasses

Glass of the composition 23B2O3-5ZnO-72Bi2O3-xCuO (where, x=0.0003, 0.0012 and 0.003 at%, in excess) were prepared by a melt-quench technique. The effects of the copper ions on the structural and optical properties of ZnO-Bi2O3-B2O3 glass matrix were analyzed using various spectroscopic techniques. The infrared spectra showed the presence of some bands that are assigned to vibrations of Bi-O bonds from BiO6 octahedral units and B-O bonds from BO3 and BO4 units. The electron paramagnetic resonance spectra revealed the presence of Cu2+ ions in the glass structure in an axially distorted octahedral environment. The number of Cu2+ ions participating in resonance and its paramagnetic susceptibility has been evaluated. The UV-vis spectra show a broad absorption band at 785 nm and another band at 438 nm which are due to d-d transitions of Cu2+ ions. These glasses are found to exhibit visible and near infrared luminescence bands centered at 548 and 652, and 804 nm when excited at 400 and 530 nm, respectively. The luminescence centers are supposed to be caused by the lower valence state of bismuth, such as Bi2+ and Bi+ ions, generated during in-situ redox reactions.