Ln₂Te₆O₁₅(Ln = La, Gd, and Eu) "Anti-Glass" Phase-Assisted Lanthanum-Tellurite Transparent Glass-Ceramics: Eu³⁺Emission and Local Site Symmetry Analysis

The presence of lanthanide-tellurite "anti-glass" nanocrystalline phases not only affects the transparency in glass-ceramics (GCs) but also influences the emission of a dopant ion. Therefore, a methodical understanding of the crystal growth mechanism and local site symmetry of doped luminescent ions when embedded into the precipitated "anti-glass" phase is crucial, which unfolds the practical applications of GCs. Here, we examined the Ln₂Te₆O₁₅"anti-glass" nanocrystalline phase growth mechanism and local site symmetry of Eu³⁺ions in transparent GCs produced from 80TeO₂-10TiO₂-(5 - x)La₂O₃-5Gd₂O₃-xEu₂O₃glasses, where x = 0, 1, 2. A crystallization kinetics study identifies a unique crystal growth mechanism via a constrained nucleation rate. The extent of "anti-glass" phase precipitation and its growth in GCs with respect to heat-treatment duration is demonstrated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis. Qualitative analysis of XRD confirms the precipitation of both La₂Te₆O₁₅and Gd₂Te₆O₁₅nanocrystalline phases. Rietveld refinement of powder X-ray diffraction patterns reveals that Eu³⁺ions occupy "Gd" sites in Gd₂Te₆O₁₅over "La" sites in La₂Te₆O₁₅. Raman spectroscopy reveals the conversion of TeO₃units to TeO₄units with Eu₂O₃addition. This confirms the polymerizing role of Eu₂O₃and consequently high crystallization tenacity with increasing Eu₂O₃concentration. The measured Eu³⁺ion photoluminescence spectra revealed its local site symmetry. Moreover, the present GCs showed adequate thermal cycling stability (∼50% at 423 K) with the highest activation energy of around 0.3 eV and further suggested that the present transparent GCs would be a potential candidate for the fabrication of red-light-emitting diodes (LEDs) or red component phosphor in W-LEDs.