Concentration effects in erbium doped tellurite glass

We spectroscopically investigate heavily erbium doped sodium-zinc-tellurite glass as a possible fibre laser medium. Excited state lifetimes are derived using Judd-Ofelt theory and are compared with measurements. These lifetimes are found to be strongly dependent on erbium ion concentration, probably due to upconversion processes. Tellurite glass is thus a good candidate for upconversion lasing.