Cs₂NaGdCl₆:Tb³⁺─A Highly Luminescent Rare-Earth Double Perovskite Scintillator for Low-Dose X-ray Detection and Imaging

Rare-earth-based double perovskite (DP) X-ray scintillators have gained significant importance with low detection limits in medical imaging and radiation detection owing to their high light yield (LY) and remarkable spatial resolution. Herein, we report the synthesis of 3D double perovskite (DP) crystals, namely, Cs 2 NaGdCl 6 and Tb 3+ -Cs 2 NaGdCl 6 using hydrothermal reaction. Cs 2 NaGdCl 6 DP single crystals exhibited a blue self-trapped exciton (STE) emission at 470 nm under ultraviolet (265 nm) excitation with a photoluminescence quantum yield (PLQY) of 8.4%. Introducing Tb 3+ ions into Cs 2 NaGdCl 6 has resulted in quenching of STE emission and enhancing green emission at 549 nm attributed to the 5 D 4 → 7 F 5 transition of Tb 3+, suggesting efficient energy transfer (ET) from STE to Tb 3+ . This ET process is evidenced by the appearance of Tb 3+ bands in the excitation spectra of the host, the shortening of the STE lifetimes in the presence of Tb 3+ ions, and the enhancement of PLQY (72.6%). Furthermore, Cs 2 NaGdCl 6:5%Tb 3+ films of various thicknesses (0.1–0.6 mm) were synthesized and their X-ray scintillating performance has been examined. The Cs 2 NaGdCl 6:5%Tb 3+ film with 0.4 mm thickness has exhibited an excellent linear response to the X-ray dose rate with a low detection limit of 41.32 nGy air s –1, an LY of 39,100 photons MeV –1, and excellent radiation stability. Benefiting from the strong X-ray excited luminescence (XEL) of Cs 2 NaGdCl 6:5%Tb 3+, we developed a Cs 2 NaGdCl 6:5%Tb 3+ X-ray scintillator screen with a least thickness (0.1 mm), exhibiting remarkable imaging ability with a spatial resolution of 10.75 lp mm –1 . These results suggest that Cs 2 NaGdCl 6:Tb 3+ can be a potential candidate for low-dose and X-ray imaging applications.