Simultaneous Tailoring of Robust Anti-Thermal Quenching and High Thermometric Sensitivity in Lanthanide-Doped Cs2NaYF6 Double Perovskites

Lanthanide-doped double perovskites have emerged as promising candidates for remote optical thermometry owing to their pronounced thermally quenched photoluminescence. However, substantial emission attenuation at elevated temperatures poses a challenge to achieving high measurement precision. Herein, a facile solid-state synthesis of efficient lanthanide-doped fluoride double perovskites Cs 2 NaYF 6 , is reported presenting robust anti-thermal quenching behavior while maintaining enhanced thermal sensitivity through partial substitution of Na + with Li + . Li + doping induces lattice contraction and increased stiffness, reducing phonon energy and suppressing electron–phonon coupling, thereby enhancing emission intensity and mitigating the thermal quenching of Er 3+ . Meanwhile, Li + -induced local symmetry distortion around Er 3+ leads to further Stark splitting of 2 H 11/2 , promoting the thermally assisted population of green-emitting levels, which retain 84% of their initial intensity at 523 K. In contrast, the red emission remains unaffected due to the large energy gap between adjacent levels. Consequently, both thermally coupled and non-thermally coupled thermometric sensitivity are enhanced, with a maximum improvement of up to 6-fold, leading to a substantial reduction in temperature uncertainty at high temperatures. Furthermore, the practical applicability of flexible polydimethylsiloxane-based optical fiber and thin-film temperature sensors is demonstrated. This provides insights into simultaneously optimizing the intensity and sensitivity of luminescent thermometers.