Studies of Er3+ doped germanate–oxyfluoride and tellurium–germanate–oxyfluoride transparent glass–ceramics

An erbium doped germanate–oxyfluoride glass 60GeO2 · 20PbO · 10PbF2 · 10CdF2 (GPOF) and a tellurium–germanate–oxyfluoride glass 30TeO2 · 30GeO2 · 20PbO · 10PbF2 · 10CdF2 (TGPOF) were prepared in the bulk form. By appropriate heat treatment of the as-prepared glasses above, transparent glass–ceramics were obtained with the formation of β-PbF2 nanocrystals in the glass matrix confirmed by X-ray diffraction. Optical absorption and photoluminescence measurements were performed on as-prepared glass and glass–ceramics. The luminescence of Er3+ ions in transparent glass–ceramics revealed sub-band splitting generally seen in a crystal host. The intensity of red and near infrared luminescence significantly increased in transparent glass–ceramic compared to that in as-prepared glass. Two luminescence bands at 758 nm from 4F7/2 → 4I13/2 and at 817 nm from 2H11/2 → 4I13/2 transitions were observed from transparent glass–ceramic but cannot be seen from the corresponding as-prepared glass. These results are attributed to the change of ligand field of Er3+ ions and the decrease of effective phonon energy when Er3+ ions were incorporated into the precipitated β-PbF2 nanocrystals.