Abstract
Rare earth (RE) doped transparent tellurite glass-ceramics (GCs) are widely explored for their application as advanced photonic materials. Specifically, the growth of RE based “anti-glass” crystalline phases in transparent GCs enhances their effective functionality. Enormous studies on the properties of GCs revealed that optimization of glass composition and heat-treatment schedule are the foremost factors that affect the transparency of the GCs. Nevertheless, the direct effect of RE3+ ions on the crystallization mechanism of glass has hardly been reported. Therefore, a base glass of the composition La2O3–Gd2O3–TiO2–TeO2 (LGTT) is doped with RE3+ ions (Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, and Dy3+) with varied ionic radii. Rietveld refinement from XRD of GCs confirms that (La/Gd)2Te6O15 phases are precipitated, where dopants Ce, Pr and Nd occupy La sites, while Sm, Eu, Tb, and Dy occupy Gd sites. The configurational heat-capacity (ΔCp) from DSC is found to be lower for larger ionic radii REs (Ce, Pr, Nd) than smaller ionic radii REs (Sm, Eu, Tb, Dy) thereby exhibiting higher chemical ordering followed by faster crystal growth rate in the former. However, the transparency retention profile of different RE-doped GCs follows the trend Eu:Tb > Sm:Dy > Nd > Pr > Ce, confirming the ionic radii effect. In addition to the ionic radii effect, in this work, we propose a ‘Hole-Formalism’ concept to explain the observed trend. It is further corroborated with an identical neutron diffraction pattern and ΔCp values for these ion pairs Sm3+ : Dy3+ (4f5 : 4f9) and Eu3+ : Tb3+ (4f6 : 4f8) results in a similar crystallization mechanism, transmission profile and fine-scale microstructures of these RE-based tellurite GCs.
