Up-conversion luminescence of Er3+/Yb3+ co-doped Gd2Te6O15 tellurite glass-ceramics for optical thermometry

The Er³⁺/Yb³⁺ co-doped tellurite glasses and glass-ceramics (GCs) containing the Gd₂Te₆O₁₅ phase were successfully fabricated via the conventional melting-quenching technique followed by a crystallization regime. The Er³⁺/Yb³⁺ co-doped tellurite glasses generated intense up-conversion green (524 and 546 nm) and red (658 nm) emissions when stimulated by a 980 nm laser. The up-conversion green emission intensity increased by 68 and 46 times with the increase of the Yb³⁺/Er³⁺ ratio, and the optimal Yb³⁺/Er³⁺ ratio was found to be 8:1. The surface crystallization process of the Gd₂Te₆O₁₅ GCs was confirmed through analysis of crystallization kinetics and microscopic morphology. The up-conversion luminescence and lifetime of Er³⁺ ions were enhanced by the precipitation of low-phonon-energy Gd₂Te₆O₁₅ crystals. The GC sample crystallized at 480°C for 4 h showed the highest luminescence intensity. The optical thermometry properties of Er³⁺ ions at thermally coupled energy levels (²H_11/2/⁴S_3/2→⁴I_15/2) were explored. The Gd₂Te₆O₁₅ GCs co-doped with 0.25 mol% Er₂O₃ and 2.0 mol% Yb₂O₃ exhibited an excellent temperature relative sensitivity (S_r) of 1.22% K⁻¹ at 293 K and a great repeatability of 98.07%. These results suggest that the Er³⁺/Yb³⁺ co-doped Gd₂Te₆O₁₅ GCs show promise for optical thermometry.