Ln 2 Te 6 O 15 (Ln = La, Gd, and Eu) "Anti-Glass" Phase-Assisted Lanthanum-Tellurite Transparent Glass-Ceramics: Eu 3+ 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 LnTeO "anti-glass" nanocrystalline phase growth mechanism and local site symmetry of Eu ions in transparent GCs produced from 80TeO-10TiO-(5 - )LaO-5GdO-EuO glasses, where = 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 LaTeO and GdTeO nanocrystalline phases. Rietveld refinement of powder X-ray diffraction patterns reveals that Eu ions occupy "Gd" sites in GdTeO over "La" sites in LaTeO. Raman spectroscopy reveals the conversion of TeO units to TeO units with EuO addition. This confirms the polymerizing role of EuO and consequently high crystallization tenacity with increasing EuO concentration. The measured Eu 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.