Copper ion as a structural probe in lead bismuth arsenate glasses by means of dielectric and spectroscopic studies

PbO-Bi2O3-As2O3 glasses mixed with different concentrations of CuO (ranging from 0 to 0.6 mol%) were prepared. Dielectric properties (viz., dielectric constant ε', loss tan δ and a.c. conductivity σac) over a wide range of frequency and temperature as a function of concentration of CuO have been investigated. Optical absorption, luminescence, ESR, IR spectral studies have also been carried out. The analysis of results of the dielectric properties has revealed that the glasses possess high insulating character when the concentration of CuO is >0.3 mol%. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 0.3 mol%. In the high-temperature region, the a.c. conduction seems to be connected with the mixed conduction, viz., electronic and ionic conduction. The optical absorption spectra of these glasses exhibited bands due to Cu+ ions in the UV region in addition to the conventional band due to Cu2+ ions in the visible region. Further two prominent kinks attributed to 3P0→1S0, 1D2 transitions of Bi3+ ions have also been located in the absorption spectra. The luminescence spectra excited at 275 nm have exhibited an intense green emission band centered at about 555 nm and a relatively broad blue emission band at about 455 nm; these bands have been attributed to the 3D1→1S0 transition of isolated Cu+ ions and 3D1→1S0 transition of (Cu+)2 pairs respectively. The quantitative analysis of the results of all these studies has indicated that as the concentration of CuO is increased beyond 0.3 mol% in the glass matrix, a part of Cu2+ ions has been reduced to Cu+ ions exhibiting a strong bearing on physical properties of these glasses.