Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi2O3-P2O5 glass with low-P2O5 content (20–25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF2. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF2 substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s–6p interband transition in Bi3+ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.