Removal of hydroxyl groups to enhance the near- and mid-infrared emission of heavy-metal oxyfluoride glasses by chemical clarification : Nitrate ions

The near- and mid-infrared emission of rare-earth-doped glasses has many applications in civilian and military fields, but the overlapping vibrations of soluble hydroxyl groups in the glass matrix restrict the emission intensity. To reduce the quenching effects of the hydroxyl groups on the near- and mid-infrared emission, nitrate ions as a chemical clarificant, which are added to the raw materials for the preparation of heavy-metal oxyfluorotellurite glasses, can decompose during the melting process and release a large amount of gases to remove OH- from the molten glass. The results reveal the emission intensity is noticeably enhanced and the absorption coefficient of OH- is substantially reduced. Judd-Ofelt analysis and related calculations demonstrate the J-O parameter Omega(2) decreases and Omega(4) increases slightly with the decrease of OH- content, and, at the same time, the stimulated absorption and emission cross sections also increase when the amount of nitrate is within a certain range. Especially, the intensity of the mid-infrared emission near 3 mu m upon addition of 0.6 mol% Pb(NO3)(2) is enhanced severalfold compared with that without nitrate ions.