Structural, optical and thermal properties of glass and anti-glass phases in strontium tellurite and borotellurite systems doped with europium

Highlights: • Optical, thermal and structural properties of SrO-TeO₂ and SrO-B₂O₃-TeO₂ glasses containing Eu³⁺. • Co-existing glass and SrTe₅O₁₁ anti-glass inclusions in 10SrO-90TeO₂ sample. • Rectangular, triangular, spherical and flower shaped inclusions in the samples. • 1-mol% Eu₂O₃ modifies the shape and size of the inclusions. • B₂O₃ suppresses the growth of anti-glass inclusions and enhances Eu³⁺ fluorescence. - Abstract: Glass sample of the composition: 10SrO-90TeO₂ was prepared by melt-quenching technique and found to contain triangular, rectangular, and spherical shaped micro-inclusions of the average size ∼803 μm in the glassy matrix. The inclusions grow to an average size of ∼1347 μm and assume flower-like morphology upon adding 1 mol% Eu₂O₃ in the 10SrO-90TeO₂ sample. X-ray diffraction studies showed that the micro-inclusions exhibit sharp peaks, but their Raman spectra have broad phonon bands that are indistinguishable or very similar to that of the glassy matrix phase. The addition of 10 mol% B₂O₃ in the samples inhibits the growth of inclusions of anti-glass phases and forms purely amorphous samples. B₂O₃ significantly enhances the photoluminescence properties of Eu³⁺ doped samples. Furthermore, B₂O₃ converts the four-fold co-ordinated Te-O structural units into three-fold co-ordinated Te-O units.