Eu 3+ ‐Activated Single‐Band Ratiometric Nanothermometry by Lattice Negative Thermal Expansion

Abstract Single‐band ratiometric (SBR) thermometry has recently emerged as a powerful alternative to its dual‐emission counterparts because it can avoid the large uncertainties related to the emission spectral overlap or light absorption/scattering by the medium. Herein, a novel SBR thermometric scheme in Sc 2 Mo 3 O 12 :Eu 3+ nanosheet that depends on thermal enhancement of charge‐transfer state absorption between O 2− and Eu 3+ is reported. Mechanistic investigation reveals the vital role of the lattice negative thermal expansion (NTE) for thermally enhanced Eu 3+ emissions according to the configuration coordinate model. In contrast, serious thermal quenching of Eu 3+ emissions is detected under the excitation wavelength corresponding to ground state absorption. Such excitation wavelength‐dependent thermal behavior of luminescence enabled SBR thermometry with high sensitivity and resolution ( S r = 2.0% K −1 , δT = 0.121 K at 363 K). Finally, the applicability of the proposed SBR model to real‐world sensing scenarios is demonstrated using the as‐fabricated flexible thin‐film, offering accurate and real‐time temperature detection at the local hotspot in the electronic component.