D3→FJ emission in terbium-doped sol-gel glasses

In silicate sol-gel glass doped with trivalent terbium, the intensity of violet and blue fluorescence from the ⁵D₃ level is highly dependent on terbium concentration, on the presence of Al³⁺ co-dopant, and on annealing conditions. Evidence is presented that aluminum co-doping prevents rare earth clusters from forming, and also modifies the coupling of rare earth ions to the local environment. ⁵D₃ emission is observed in glasses annealed at 750 °C, and increases in intensity with increasing annealing time and with higher temperature. This behavior is shown to be due to the removal of residual hydroxyl ions.