Thermally boosted upconversion luminescence and high-performance thermometry in ScF3:Yb3+/Tm3+ nanorods with negative thermal expansion

Luminescence nanothermometers featuring high spatial resolution and thermal resolution have aroused extensive interest in biological and nanomedical fields. However, the challenge of thermal quenching in upconversion (UC) nanocrystals hampers achieving elevated relative temperature sensitivity (Sr). In this study, the quasi cubic nanorods of ScF3:Yb3+/Tm3+ with negative thermal expansion were prepared, and thermally boosted luminescence was found to derive from the phonon-assisted energy transfer, resulting in the emission band of 3F2,3 → 3H6 of Tm3+ ions enhanced monotonously. While the emission bands of (1G4)1D2→3F4 of Tm3+ ions first increased slightly and then decreased seriously because of the competition between phonon-assisted and cross-relaxation (CR) processes. Relying on this high-contrast thermal dependent feature, the maximum relative sensitivity of 1.60% K−1 at 523 K was achieved in the proposed luminescence intensity ratio (LIR) thermometry. These findings would open a new avenue for designing thermally boosted upconversion nanocrystals and reliable optical thermometers by using Tm3+ activated luminescent materials.