Effect of Bi2O3 proportion on physical, structural and electrical properties of zinc bismuth phosphate glasses

The variation in physical, structural and electrical properties has been studied as a function of Bi2O3 content in 20ZnF2–(10 + x) Bi2O3–(70-x) P2O5, 0 ≤ x ≤ 10 mol% glasses, which were prepared by melt quenching technique and characterized by differential thermal analysis (DTA). Colorless samples, which have no absorption peaks, are obtained for 10 and 12 mol% of Bi2O3 and the glasses are slowly becoming brownish from 15 to 20 mol% of Bi2O3 which exhibit two absorption peaks at ~ 370 nm, ~ 450 nm correspond to Bi° transitions 4S3/2 → 2P3/2 and 4S3/2 → 2P1/2 respectively. The decrease in 3P1 → 1S0 transition of Bi3+ photo luminescence emission for 18 and 20 mol% of Bi2O3 and increase in optical absorption area shows the reduction of Bi3+ to Bi°. From FTIR studies it is observed that an addition of Bi2O3 decreases the P―O―P covalent bond by forming P―O―Bi bonds due to high polarizing nature of Bi3+ ions. Dielectric parameters like εʹ, tan δ and a.c. conductivity σac are found to increase and activation energy for a.c. conduction is found to decrease with the increase in the concentration of Bi2O3. Density of defect energy states is found to increase for higher concentration of Bi2O3 and is discussed according to quantum mechanical tunneling (QMT) model.