Efficient radioactive gas detection by porous metal-organic framework scintillating nanocrystals.

Natural radioactive gases and anthropogenic radionuclides such as radon, xenon, hydrogen and krypton isotopes, need to be carefully monitored to be properly managed as pathogenic agents, radioactive diagnostic agents or indicators of nuclear activity. State-of-the-art gas detectors based on liquid scintillators suffer from many drawbacks such as lengthy sample preparation procedures and limited solubility of gaseous radionuclides, which produces a detrimental effect on measurement sensitivity. A potential breakthrough solution to this problem is using solid porous scintillators that act as gas concentrators and, therefore, could increase detection sensitivity. Highly porous scintillating metal-organic frameworks (MOFs) stand out as relevant materials for the realization of these devices. We demonstrate the capability of porous hafnium-based MOF nanocrystals exploiting dicarboxy-9,10-diphenylanthracene (DPA) as a scintillating conjugated ligand to detect gas radionuclides. The nanocrystals show fast scintillation properties in the nanosecond domain, a fluorescence quantum yield of ~40% and an accessible porosity suitable to host noble gas atoms and ions. The adsorption and detection of radionuclides such as 85Kr, 222Rn and 3H have been explored for these MOFs utilising a newly developed device based on a time coincidence technique. MOF nanocrystals demonstrate an improved sensitivity for these radionuclides compared to a reference detector, showing an excellent linear response down to an activity value lower than 1 kBq·m-3 that outperforms commercial devices. These results strongly support the possible use of scintillating porous MOF nanocrystals as the building block of ultrasensitive sensors for detecting natural and anthropogenic radioactive gases.