Influence of the preparation conditions of erbium-doped bismuth germanate glasses on its optical response

• Strong effects of the glass preparation conditions and of the thermal annealing treatments on the optical properties.
• Bi nanoparticle formation in thermally annealed glasses obtained after melting at high temperature.
• Hysteretic transmission versus temperature behavior under heating-cooling cycles of Bi nanoparticle-containing glasses.
• Bi2O3-containig glasses can be very useful for applications such as broadband amplifiers and thermo-optical devices.

The influence of the glass preparation conditions (melting temperature and crucible material) and of post-preparation heat treatments on the refractive index, optical absorption and near infrared luminescence of an Erbium-doped Bi2O3-GeO2 glass has been studied. The optical absorption and emission are strongly dependent on these conditions and Bi to Er energy transfer is observed to occur. In some cases, a high absorption due to the formation of Bi nanoparticles is obtained. Consequently transmission-temperature hysteresis loops during heating-cooling cycles are observed due to the reversible melting and solidification of nanoparticles. Our results indicate that, with adequate composition and preparation conditions, bismuth germanate glasses can be very useful for a large variety of optical devices, such as amplifiers and thermo-optical modulators and filters.