Highly Transparent Fluorotellurite Glass-Ceramics: Structural Investigations and Luminescence Properties

Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel compounds and control the optical properties of resulting glass-ceramics. Here, we report on a crystallization study of the ZrF₄-TeO₂ glass system and show that under specific synthesis conditions, a previously unreported Te_0.47Zr_0.53O_xF_y zirconium oxyfluorotellurite antiglass phase can be selectively crystallized at the nanometric scale within the 65TeO₂-35ZrF₄ amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near-infrared ranges. Under longer heat treatment, the stable cubic ZrTe₃O₈ phase crystallizes in addition to the previous unreported antiglass phase. The structure, microstructure, and optical properties of 65TeO₂-35ZrF₄Tm³⁺-doped glass-ceramics, were investigated in detail by means of X-ray diffraction, scanning and transmission electron microscopies, and ¹⁹F, ⁹¹Zr, and ¹²⁵Te NMR, Raman, and photoluminescence spectroscopies. The crystal chemistry study of several single crystals samples by X-ray diffraction evidence that the novel phase, derived from α-UO₃ type, corresponds in terms of long-range ordering inside this basic hexagonal/trigonal disordered phase (antiglass) to a complex series of modulated microphases rather than a stoichiometric compound with various superstructures analogous to those observed in the UO₃–U₃O₈ subsystem. These results highlight the peculiar disorder–order phenomenon occurring in tellurite materials.