Structural influence of tellurite glasses on fluorescence of thulium near 1.86 μm

The need for inexpensive lasing material for the region 1.6–2.0 μm has led to the investigation at our laboratories, of thulium doped tellurite glasses. A range of alkali tellurite and alkaline earth tellurite glasses with variable thulium content was studied by optical techniques. For continuous wave excitation at 795 nm, emission intensities around 1860 nm were compared to those of a standard Tm:YAP crystal of known quantum yield. To allow calculation separately of radiative and non-radiative components of the de-excitaftion, the fluorescence decay rates under pulsed excitation at 795 nm were measured. For the glasses, typical radiative lifetimes of ≈2 ms, with dopant–host de-excitation lifetimes of around 5 ms were calculated. For concentrations of thulium oxide above 0.1 mol%, dopant–dopant quenching of dipole–dipole form became significant. At 0.2 mol%, the fluorescent output per unit volume was maximum. The quantum efficiency was around 0.7 for dilute concentration of thulium oxide, and only 0.25–0.30 for 0.2 mol% of thulium.