Mid-infrared fluorescence properties, structure and energy transfer around 2 µm in Tm³⁺/Ho³⁺ co-doped tellurite glass

Highlights: • Tellurite glasses with good thermal stability and low phonon energy are prepared. • 1.8 µm, enhanced near 2 µm and a weak 2.3 µm fluorescences are observed. • The micro-parameters of the energy transfer are evaluated and analyzed. • The decay lifetime of 2 µm fluorescence reaches to 2.46 ms. • The Tm³⁺/Ho³⁺ co-doped tellurite glass is a promising material for 2 µm laser. - Abstract: Tm³⁺/Ho³⁺ doped tellurite glasses with good thermal stability and low phonon energy are prepared. 1.8 µm fluorescence, enhanced near 2 µm fluorescence and a weak 2.3 µm fluorescence are observed in the Tm³⁺/Ho³⁺ co-doped glasses. The energy transfer mechanism between Tm³⁺ and Ho³⁺ has been analyzed according to the absorption spectra, the emission spectra and the level structures of Tm³⁺ and Ho³⁺ ions. The decay lifetime of 1.8 µm and 2 µm fluorescence in Tm³⁺/Ho³⁺ co-doped tellurite glass are 0.38 ms and 2.46 ms, respectively. Moreover, the energy transfer efficiency between Tm³⁺:³F₄ and Ho³⁺:⁵I₇ levels is calculated and compared. Additionally, the calculated forward energy transfer coefficient C_Tm-Ho is about five times as large as the reverse energy transfer coefficient C_Ho-Tm. Results demonstrate that the Tm³⁺/Ho³⁺ doped tellurite glass has excellent spectroscopic properties and can be an attractive candidate for 2 µm laser.