<p>Compositionally engineered metal-organic frameworks are designed and used to fabricate ultrafast scintillating films. The inclusion of hafnium ions in the nodes of the metal-organic framework enhances the interaction with ionizing radiation, partially compensating for the low density of the porous material and increasing the scintillation yield. The high diffusivity of molecular excitons within the framed conjugated ligands allows bimolecular annihilation processes that partially quench the system luminescence, resulting in fast scintillation pulses in the hundreds of picoseconds time scale. Despite the quenching, the gain in scintillation yield achieved is large enough to maintain the film light yield above 10⁴ph MeV^-1 under soft X-rays. These high efficiencies and fast emission kinetics are obtained at room temperature in a technologically attractive solid-state configuration, placing the metal-organic framework platform in a prominent position for the realization of the next generation of fast scintillation counters for high-energy physics studies and medical imaging applications.</p>