Gel-route synthesis of lanthanide-organic frameworks for cryogenic thermometry, scintillation, and DMF sensing

Here, we report a rapid gel-route synthesis of lanthanide-organic frameworks (LOFs) based on 1,3,5-benzenetricarboxylic acid (H 3 BTC) or 1,3,5-tris(4-carboxyphenyl)benzene (H 3 BTB) with Gd 3+ , Eu 3+ , and Tb 3+ ions, including mixed Eu 3+ /Tb 3+ systems. The resulting xerogels (X-Ln-BTC and X-Ln-BTB) displayed crystalline structures corresponding to MOF-76 (73% crystallinity) and MIL-103 (44% crystallinity), representing the first demonstration of these frameworks via gel-based synthesis. Rheological analyses confirmed gel-like behavior, while X-ray fluorescence mapping verified homogeneous lanthanide distribution. The gels exhibited quantum yields of 10.2-36.4% and efficient Tb 3+ → Eu 3+ energy transfer, reaching up to 93% efficiency for the Eu 0.05 Tb 0.95 -BTB. Under X-ray excitation (12 keV), the materials demonstrated scintillation with sharp emission lines. As luminescent thermometers (15-225 K), X-Eu 0.1 Tb 0.9 -BTC achieved maximum sensitivity (S m ) of 1.7 %K -1 at 15 K, while X-Eu 0.05 Tb 0.95 -BTC demonstrated 1.62 %K -1 at 15 K with Sᵣ > 1 %K -1 in the cryogenic range (15-45 K), outperforming other Eu/Tb-BTC systems. X-Eu 0.05 Tb 0.95 -BTB exhibited selective, reversible DMF vapor detection. This study presents a versatile gel-to-LOF synthesis enabling multifunctional luminescent materials for cryogenic thermometry, X-ray scintillation, and vapor sensing.