Fast Luminescent MOFs for Scintillation and Photon Management

Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely used as radiation detectors. Specifically, scintillators with fast timing characteristics are essential for achieving high-resolution imaging at the millimetre length scale, particularly in medical imaging and tomography, e.g., Time-of-Flight Positron Emission Tomography (ToF-PET). We demonstrated that composite materials made with fluorescent metal-organic framework (MOF) nanocrystals embedded in a polymer matrix can serve as fast scintillators.[1] In these nanocrystals, the synergy between the high-Z inorganic nodes and the fast-emitting diphenylanthracene (DPA) organic ligand, arranged at nanometric distances within the framework, enabled the rapid and efficient sensitization of ligand fluorescence. The hybrid composite scintillator exhibited a fast time response (τscint ~ 4 ns) and an ultra-fast scintillation rise time of ~50 ps, making it a promising material for time-resolved applications. Fast emitters with large Stokes shifts are highly desirable because of the negligible reabsorption of their luminescence. This aim was achieved by inserting two fluorescent building blocks within the MOF nanocrystals.[2,3] We realized hetero-ligand MOFs with a Stokes shift as large as 1.3 eV by co-assembly scintillating ligands with complementary emission and absorption properties. The unique electronic properties of the conjugated ligands allowed for the sensitization of emissive ligands by means of an ultra-fast diffusion-mediated non-radiative energy transfer that occurs at rates in the THz range. This efficient mechanism enabled the instantaneous activation of the ns-lifetime scintillation emission of these MOFs. Remarkably, the efficient antenna mechanism and the elimination of reabsorption improved the scintillation yield of the hetero-ligand MOF by 500% compared to the parent MOF. Recently, we proposed the fabrication of MOF thin films (thickness ~ 20 μm) on glass substrates using a solvothermal strategy to produce all-solid-state scintillators.[4] The optimized composition, comprising Hf-oxo-hydroxy clusters and complementary emitting ligands, yields the shortest scintillation time achieved to date for MOF-based systems (τscint ~ 150 ps) and generates highly emissive MOFs that exhibit a light yield of 12000 ph/MeV. Thus, scintillating MOF thin films appear to be appealing candidates for the realization of next-generation ultrafast multicomponent scintillation counters. References [1] J. Perego, I. Villa, A. Pedrini, E. C. Padovani, R. Crapanzano, A. Vedda, C. Dujardin, C. X. Bezuidenhout, S. Bracco, P. E. Sozzani, A. Comotti, L. Gironi, M. Beretta, M. Salomoni, N. Kratochwil, S. Gundacker, E. Auffray, F. Meinardi and A. Monguzzi, Nat. Photon., 15, 393 - 400 (2021). [2] M. Orfano, J. Perego, C. X. Bezuidenhout, I. Villa, R. Lorenzi, B. Sabot, S. Pierre, S. Bracco, S. Piva, A. Comotti, and A. Monguzzi, Adv. Funct. Mater., 34, 2404480 (2024). [3] J. Perego, C. X. Bezuidenhout, I. Villa, F. Cova, R. Crapanzano, I. Frank, F. Pagano, N. Kratochwil, E. Auffray, S. Bracco, A. Vedda, C. Dujardin, P. E. Sozzani, F. Meinardi, A. Comotti and A. Monguzzi, Nat. Commun., 13, 3504 (2022). [4] L. Dhamo, J. Perego, I. Villa, C. X. Bezuidenhout, I. Mattei, A. Landella, S. Bracco, A. Comotti, and A. Monguzzi, Nat. Commun., ASAP article (2025).