Photothermal and spectroscopic characterization of Tb3+-doped tungsten–zirconium–tellurite glasses

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.