Zn2+/Ge4+ heterovalent co-substitution for enhancing upconversion luminescence and temperature-sensing properties of Er3+-doped garnets

Zn 2+ /Ge 4+ heterovalent co-substitution enables charge compensation and modifies the Er 3+ crystal field in garnet solid solutions. • Upconversion intensity of Er 3+ is enhanced over 4-fold for green emission and 3-fold for red emission. • The FIR thermometry exhibits excellent performance, achieving S r = 1.20% K −1 (@298 K) and δT ∼0.41 K. Heterovalent cation co-substitution is an effective strategy to regulate the crystal field and luminescence in rare-earth-doped phosphors. Here, Er 3+ -activated garnet solid solutions Gd 3 Zn x Ga 5–2 x Ge x O 12 ( x = 0.5–2) (GZG 5–2 x G) were synthesized via the solid-state reaction. A Zn 2+ /Ge 4+ pair was introduced to replace two Ga 3+ ions, enabling charge compensation and modifying the crystal field of Er 3+ . With Zn 2+ /Ge 4+ composition variation, the upconverison of green emission dominates at x  = 0.5, while red emission peaks at x  = 1. The Zn 2+ /Ge 4+ co-substitution significantly enhances luminescence, with GZG 4 G:10%Er 3+ and GZG 3 G:10%Er 3+ exhibiting over 4-fold (green upconversion) and 3-fold (red upconversion) intensity enhancement compared to GZGG:10%Er 3 + . The optical thermometry was constructed over 298–573 K, with a maximum relative sensitivity (S r ) of 1.20% K −1 and a minimal temperature resolution (δ T ) of ∼ 0.41 K at 298 K. The results demonstrate that the Zn 2+ /Ge 4+ co-substitution effectively tunes the upconversion emission and thermometric performance of Er 3 + -doped garnets, offering a feasible strategy for optimizing garnet-based optical temperature sensors. Download: Download high-res image (189KB) Download: Download full-size image