Publication

Abstract :

Among the glassy materials, tellurite glasses exhibit low phonon energy (∼780 cm⁻¹), good mechanical stability, chemical durability, and high linear and nonlinear refractive indices, with a wide transmission window (typically 0.4–6.0 μm), which make them promising materials for photonic applications. In this work, tungsten–zirconium–tellurite glasses doped with several Tb³⁺ concentrations (0.1–4.0 mol. % Tb₂O₃) were prepared and characterized through absorption, emission, excitation spectra and fluorescence decay rate measurements. Only the green/yellow emission due to the ⁵D₄ level was observed since the ⁵D₃ was not observed in either the absorption or emission spectra due to cutoff absorption of the host matrix at ∼470 nm. A concentration quenching effect was observed in the 545 nm green emission (⁵D₄ → ⁷F₅) with a critical Tb³⁺ concentration of 6.2×10²⁰ cm³ (1.7 mol. %). Thermal lens (TL) was performed in order to determine the thermo-optical properties of the glass such as thermal diffusivity (D ∼ 3.3×10⁻³ cm²/s) and optical path temperature coefficient (ds/dT ∼ 2.5 × 10⁻⁵ K⁻¹). The energy transfer efficiency from the host matrix to the Tb³⁺ was estimated from excitation spectra as ∼3%, in agreement with TL measurements which indicate that nearly all absorbed energy is converted into heat for 488 nm excitation (⁷F₆ → ⁵D₄). Z-scan measurements in the cw regime indicate a dominant thermal nonlinearity in agreement with TL data. However, the fluorescence measurements in the Z-scan indicate a strong saturation of the green fluorescence attributed to the effect of excited state absorption.