To eliminate the self-absorption of the luminescence to maximize the light output is crucial in many photonic applications, especially in the case of luminescent scintillators employed to monitor the ionizing radiations. A dramatic luminescence re-absorption hinders indeed their use where large Stokes shift fast emitters are needed for the acquisition of high-quality images in short time frames, such as ToF-PET imaging for the detection of high-rate/high-energy events to avoid detrimental pile-up of the recorded emitted photons, or to realize sensitive detectors for rare events, such as in the activity quantification of gas radionuclides.
In the article “Reabsorption-free scintillating hetero-ligand MOF crystals activated by ultrafast energy transfer” (doi: 10.1002/adfm.202404480), published in the journal Advanced Functional Materials (Wiley, Impact Factor 18.5, 2023 Journal Impact Factor, Journal Citation Reports (Clarivate Analytics, 2024)), the research theme led by Prof. Angiolina Comotti and Prof. Angelo Monguzzi developed new hybrid metal-organic frameworks (MOF) scintillating fast zero-resorption crystals in collaboration with the Commissariat à l'énergie atomique et aux énergies alternatives (CEA) in Paris, France.
In this work, the MOF composition was engineered with the use of different ligands with closely complementary emission and absorption properties and highly delocalized molecular electronic orbitals. This enables the fluorescence activation of the ligand at lower energy through an ultrafast nonradiative energy transfer in the terahertz regime, resulting in a Stokes shift of the emission of 1.3 eV, which allows for a 500% increase in scintillator light output and a consequent 20% improved sensitivity in the detection of gaseous radionuclide gases of radioactive isotopes.