Heavy atom-doped thermally activated delayed fluorescence cesium zirconium halides for efficient X-ray imaging

Metal halide scintillators have received extensive attention for their application in medical and industrial fields. However, it is extremely difficult for most reported scintillators to achieve the optimal balance among X-ray absorption capability, exciton utilization efficiency, and photoluminescence quantum yield. Here we introduce heavy atoms (Hf) with a similar ionic radius into the Cs2ZrCl6 structure to synthesize a vacancy-ordered double perovskite Cs2ZrCl6:Hf scintillator. Interestingly, the scintillator with a lower energy gap Ea1 and smaller Delta E(S1-T1) exhibits an energy transfer from the triplet state to the singlet state under X-ray radiation, realizing the effective utilization of triplet excitons. Meanwhile, an abnormal long decay lifetime and a higher thermal activation energy (Ea2) of the scintillator are obtained as the temperature rises, indicating that the nonradiative recombination can be suppressed. As a result, a high photoluminescence quantum yield of 93% combined with strong X-ray absorption capability enables a record high light yield of 57 000 photons per MeV. More importantly, it has a low detection limit of 338.08 nGyair s-1 and a spatial resolution of 14.7 lp mm-1, as well as good irradiation stability. Such an excellent scintillation performance and good irradiation stability lay a good foundation for efficient X-ray imaging. A heavy atom (Hf)-doped Cs2ZrCl6 scintillator with strong blue emission, large Stokes shift, and smaller Delta E(S1-T1) shows a higher light yield, a low detection limit, and a higher spatial resolution, as well as good irradiation stability.