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

Abstract

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 E_a1 and smaller ΔE_(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 (E_a2) 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 nGy_air 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.