Enhanced 1.80 μm fluorescence in Er3+/Yb3+/Tm3+ tri-doped tellurite glass for fiber lasers

Highlights: • Er³⁺/Yb³⁺/Tm³⁺ tri-doped tellurite glass with WO₃ was prepared by melt-quenching method. • Addition of WO₃ improved 1.80 μm fluorescence of Tm³⁺ due to enhanced energy transfer. • Energy transfer mechanism was investigated by calculating phonon contribution ratio. • The prepared tellurite glass with WO₃ exhibited good thermal stability. Improving the lasing emission property of rare-earth doped vitreous material is a research topic. In this paper, Er³⁺/Yb³⁺/Tm³⁺ tri-doped tellurite glasses with and without WO₃ component were synthesized using melt-quenching technique and the effect of WO₃ addition on the 1.80 μm band fluorescence of Tm³⁺ was investigated. The obtained samples were characterized by X-ray diffraction (XRD) pattern, differential scanning calorimeter (DSC) curve, Raman spectrum, UV/Vis/NIR absorption spectrum, near-infrared emission spectrum and fluorescence decay curve. The XRD pattern confirmed amorphous structural nature of synthesized tellurite glass, the DSC curve revealed good thermal stability with $\Delta T$>100 °C and the Raman spectrum displayed a stretching vibration band around 920 cm⁻¹ for glass host with WO₃. Under the excitation of 980 nm laser diode (LD), the intense 1.80 μm band fluorescence of Tm³⁺ originated from the ³F₄→³H₆ transition was observed in the Er³⁺/Yb³⁺/Tm³⁺ tri-doped tellurite glass and the intensity increases further with the addition of a certain amount of WO₃, which is attributed to the enhanced energy transfers from Yb³⁺ (Er³⁺) to Tm³⁺ ions due to the increased phonon energy of glass host. The energy transfer mechanism between them was elucidated by analyzing fluorescence decay behavior of Tm³⁺ and quantitatively calculating energy transfer coefficient as well as phonon contribution ratio. Meanwhile, based on the absorption spectrum, some important spectroscopic parameters such as Judd-Ofelt parameter, spontaneous radiative transition probability, fluorescence branching ratio, absorption and emission cross-sections, and gain coefficient spectrum were calculated to reveal spectroscopic properties of doped Tm³⁺ ions. The obtained results indicate that Er³⁺/Yb³⁺/Tm³⁺ tri-doped tellurite glass with an appropriate amount of WO₃ is a promising gain medium applied for the 1.80 μm band solid-state lasers.