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

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, Cs₂NaGdCl₆ and Tb³⁺-Cs₂NaGdCl₆ using hydrothermal reaction. Cs₂NaGdCl₆ 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 Tb³⁺ ions into Cs₂NaGdCl₆ has resulted in quenching of STE emission and enhancing green emission at 549 nm attributed to the ⁵D₄ → ⁷F₅ transition of Tb³⁺, suggesting efficient energy transfer (ET) from STE to Tb³⁺. This ET process is evidenced by the appearance of Tb³⁺ bands in the excitation spectra of the host, the shortening of the STE lifetimes in the presence of Tb³⁺ ions, and the enhancement of PLQY (72.6%). Furthermore, Cs₂NaGdCl₆:5%Tb³⁺ films of various thicknesses (0.1-0.6 mm) were synthesized and their X-ray scintillating performance has been examined. The Cs₂NaGdCl₆:5%Tb³⁺ 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 Cs₂NaGdCl₆:5%Tb³⁺, we developed a Cs₂NaGdCl₆:5%Tb³⁺ 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 Cs₂NaGdCl₆:Tb³⁺ can be a potential candidate for low-dose and X-ray imaging applications.