Effect of some VA group modifiers on R2O3 (RÂ =Â Sb, Bi)-ZnF2-GeO2 glasses doped with CuO by means of spectroscopic and dielectric investigations

► Effect of VA group modifiers on zinc-germanate doped with CuO glasses was studied. ► Bi2O3 effectively modified the zinc-germanate glass network than Sb2O3. ► Environment of Cu2+ ions is more ionic in Bi2O3 mixed glasses than Sb2O3 mixed glasses. ► Integration of bismuth oxide and CuO doping favours the GeO6 formation. ► The ac conductivity enhanced in Bi2O3 mixed glasses at high concentration of CuO.