Engineering Energy Transfer Through Lanthanide Dilution for Luminescence Thermometry

Predictive design strategies for high‐performance luminescent thermometers remain limited. Here, we present a new engineering approach based on dilution in pyromellitic acid‐based metal‐organic frameworks, enabling systematic control of thermometric performance through the regulation of donor‐acceptor distances and, consequently, of Tb 3+ ‐Eu 3+ energy transfer, which plays a central role in determining this performance. To achieve this, we use the optically inactive Gd 3 + ion, which allows for significant modulation of the Tb 3+ –Eu 3+ energy transfer. Furthermore, Gd 3+ dilution markedly improves thermometric performance, increasing the maximum relative sensitivity from ≈0.4% K −1 at low Eu 3+ concentrations to 1.1% K −1 for Gd 0.50 Tb 0.30 Eu 0.20 , corresponding to an enhancement of about threefold. Theoretical modeling supports the experimental results and quantitatively reproduces the dependence of energy‐transfer rates on composition and temperature. The simulations reveal that maximum sensitivity is achieved at intermediate energy‐transfer regimes, where transfer efficiency and thermal activation are optimally balanced. These findings establish dilution engineering as a versatile strategy for controlling energy‐transfer dynamics and designing high‐performance lanthanide‐based luminescent thermometers.