Relaxation dynamics of excited states of Tm3+ ions in TeO2-ZnO-Na2O-Y2O3 glasses

Tellurite glasses with the composition of xTm₂O₃-(6?x)Y₂O₃-3Na₂O-25ZnO-66TeO₂ (where 0 ≤ x ≤ 6) were obtained by the melt-quenching technique. Absorption (300 K), excitation (300 K) and fluorescence spectra (300 K) as well as fluorescence decay curves of Tm³⁺-doped title glasses are presented and discussed in details. The Judd–Ofelt analysis based on the room temperature absorption spectrum was applied for determination of fundamental fluorescence properties such as radiative transition probabilities (A_T), branching ratios (β_R), radiative lifetimes (τ_R) of the emitting levels of the Tm³⁺ ion and stimulated emission cross-sections (σ_em). Fluorescence spectra were recorded and analysed in the visible and near-infrared spectral range. The emission and effective cross-section were calculated for the ³F₄→³H₆ transition, showing that the investigated glasses are promising laser host materials, operating at 1.8 μm. The observed concentration quenching and non-exponential decay curves from the ¹G₄ and ³H₄ states indicate nonradiative energy transfer between Tm³⁺ ions. The analysis of non-exponential fluorescence decay curves from the ¹G₄ and ³H₄ levels was carried out in framework of the Inokuti-Hirayama and Yokota-Tanimoto models and energy transfer microparameters were determined. The self-quenching model was proposed for describing relaxation of the first excited state of the Tm³⁺ ion.