Tm³⁺ and Yb³⁺ co-doped tellurite glasses for short cavity optical fiber lasers: Fabrication and optical characterization

In this paper Tm-doped tellurite glasses (75TeO₂-20ZnO-5 Na ₂O, mol%) were studied and sensitization with Yb³⁺ as co-dopant was carried out in order to assess its influence on the emission properties and improve pump efficiency and wavelength emission range. Emission spectra and lifetime measurements were obtained by pumping either at 785 nm or 980 nm, thus exploiting the Yb-Tm energy transfer mechanism. Doping levels of Yb from below 1 to up 5 mol% were investigated in order to evaluate the effectiveness of energy transfer process and glasses containing an overall content of 9 mol% rare earth ions were proved to be successfully fabricated. All glasses were fully characterized from a material and spectroscopic point of view. Tellurite glasses with 4 and 1 mol% of Tm³⁺ and Yb³⁺ ions respectively were found to show a good compromise between emission efficiency and lifetime decay values. A quenching concentration of Yb ³⁺ ions up to 14 mol% was also defined for this type of glass system.