Verify the saturation of color-difference enhancement at shorter metal–metal distances

Verify experimentally whether further shortening of the metal–metal distance below the value characteristic of Gd-BTC fails to produce a substantial additional enhancement of the color difference in Tb3+, Eu3+-co-doped metal–organic frameworks.

Background

The paper examines how the metal–metal distance in Tb3+, Eu3+-co-doped metal–organic frameworks affects temperature-dependent emission color. The authors report that the color difference between low- and high-temperature emissions is largest for Gd-BTC and decreases rapidly as the metal–metal distance increases across the investigated materials.

The observed trend suggests that shortening the metal–metal distance below the value found in Gd-BTC may not substantially increase the color difference. However, the authors explicitly characterize this interpretation as a hypothesis and state that it requires experimental verification, leaving the behavior at shorter distances unresolved.

References

Importantly, the shape of the trend presented in Figure 6i directly indicates that the CD can be systematically tuned by controlling the M-M distance. Moreover, the observed relationship suggests that further shortening of the M-M distance below that characteristic of Gd-BTC would most likely not result in a substantial additional enhancement of the CD. Nevertheless, this interpretation should currently be regarded as a hypothesis and requires experimental verification in future studies.

— The Closer, the Better: Engineering RGB Thermometric Performance in Tb3+, Eu3+-Doped MOFs  (2609.16734 - Szymczak et al., 15 Sep 2026) in Results and discussion, paragraph preceding Figure 6