Redox equilibrium and NIR luminescence of Bi2O3-containing glasses

The relationship between factors affecting redox equilibrium, melting temperature, glass composition and carbon addition, and near infrared luminescence (NIR) characteristics of Bi-containing glasses was investigated, and the color center and luminescent center of these glasses were discussed based on redox equilibrium. It was found that the coloration and NIR luminescent characteristics of Bi-containing glasses are strongly affected by redox equilibrium. It was confirmed that the darkening effect (black coloration) of Bi-containing glasses is the formation process of metallic Bi colloids. The highest NIR luminescent intensity was obtained in glasses just before the beginning of darkening effect. Absorption and luminescence measurements suggest that there are few color centers and luminescent centers in these glasses. It is suggested that the color center and NIR luminescent center is likely to be caused by lower valence state species of Bi, such as Bi clusters (e.g. dimmer, tirmer, etc.) and Bi+.