Expanding broadband emission in the near-IR via energy transfer between Er³⁺-Tm³⁺ co-doped tellurite-glasses

Processes of energy transfer in Er³⁺-Tm³⁺ co-doped tellurite glasses has permitted to obtain an expanding broadband emission in the near-infrared region covering the bands S, C+L and U of the optical telecommunications and extending up to the 1700-1900 nm range under excitation by a 976 nm laser diode. This widening of the emission band is achieved through an integrated emission, where the Er³⁺ ions act as donor and the Tm³⁺ ions as acceptor following the route (Er³⁺) ⁴I_11/2→(Tm³⁺)³H₅, (Er³⁺)⁴I_13/2→(Tm³⁺) ³H₄ and (Er³⁺)⁴I _13/2→(Tm³⁺)³F₄. The relative intensity emission and lifetime of the ⁴I_13/2→ ⁴I_15/2 transition of the Er³⁺ ions decrease with increasing the Tm³⁺ concentration. Besides, high Tm³⁺ concentrations produce an emission quenching for the ³H ₄→³F₄ and ³F ₄→³H₆ radiative transitions, due to cross-relaxation between Tm³⁺ ions. These effects are studied by means of probability and quantum yield of the energy transfer. The most intense and widest emission band is measured in the glass co-doped with 0.075 and 1 mol% of Tm₂O₃ and Er₂O₃, respectively.