<p>Thermal quenching, a pervasive challenge in luminescent materials, severely limits the performance of lanthanide-based optical sensors at elevated temperatures. While negative thermal expansion (NTE) hosts have shown promise in bulk systems for countering this effect, their potential in thin-film architectures, critically for integrated photonics and miniaturized sensing, remains unexplored. Here, we demonstrate a Yb³⁺/Er³⁺ co-doped Sc₂Mo₃O₁₂ thin film that leverages anisotropic NTE dynamics to achieve 42-fold thermal enhancement in green upconversion luminescence from 300 to 560 K. <i>In situ</i> thermodiffraction and time-resolved spectroscopy reveal a dual mechanism: (1) lattice contraction along the <i>a</i>- and <i>c</i>-axes reduces the cell volume of Sc₂Mo₃O₁₂ by 11.3 ų, thereby amplifying Förster-type energy transfer (<i>k</i>_ET ∝ <i>R</i>⁻⁶) from Yb³⁺ to Er³⁺, and (2) symmetry-breaking distortions suppress nonradiative ²H_11/2 → ⁴F_9/2 relaxations, extending Er³⁺ lifetimes by 358%. Crucially, the film’s strain-engineered crystal field enables multi-modal thermometry with record sensitivities: a relative sensitivity (<i>S</i>_r) of 4.33% K⁻¹ at 300 K, and maximum <i>S</i>_r = 1.28% K⁻¹ through lifetime-based sensing, which outperforms conventional Boltzmann-limited approaches. The sub-200 nm thickness and SiO₂/Si compatibility further position this platform for on-chip integration, addressing unmet needs in high-resolution thermal mapping for quantum devices, aerospace diagnostics, and wearable sensors. This work not only deciphers the interplay between NTE and luminescence at the atomic scale but also establishes a universal strategy to design anti-thermal-quenching thin films for extreme-environment photonics.</p>