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

The Er 3+ /Yb 3+ co‐doped tellurite glasses and glass‐ceramics (GCs) containing the Gd 2 Te 6 O 15 phase were successfully fabricated via the conventional melting‐quenching technique followed by a crystallization regime. The Er 3+ /Yb 3+ 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 Yb 3+ /Er 3+ ratio, and the optimal Yb 3+ /Er 3+ ratio was found to be 8:1. The surface crystallization process of the Gd 2 Te 6 O 15 GCs was confirmed through analysis of crystallization kinetics and microscopic morphology. The up‐conversion luminescence and lifetime of Er 3+ ions were enhanced by the precipitation of low‐phonon‐energy Gd 2 Te 6 O 15 crystals. The GC sample crystallized at 480°C for 4 h showed the highest luminescence intensity. The optical thermometry properties of Er 3+ ions at thermally coupled energy levels ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) were explored. The Gd 2 Te 6 O 15 GCs co‐doped with 0.25 mol% Er 2 O 3 and 2.0 mol% Yb 2 O 3 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 Er 3+ /Yb 3+ co‐doped Gd 2 Te 6 O 15 GCs show promise for optical thermometry.