Rare earth double perovskites for underwater X-ray imaging applications†

Lanthanide metal halide double perovskites (Ln-MHDPs) are promising scintillator materials due to their outstanding luminescence properties and high X-ray absorption cross-sections. With the growing demand for advanced X-ray imaging scintillators, there is increasing interest in the exploration of new scintillation materials suitable for novel applications under harsh conditions. In this study, we present a series of Ln-MHDPs with tunable fluorescence emission spanning the visible and near-infrared regions, effectively activated by both ultraviolet and X-ray excitation. The Cs₂NaLnCl₆ (Ln = Eu, Tb, Ho, Er, and Yb) compounds demonstrated high X-ray sensitivity, excellent stability, and low detection limits under X-ray irradiation. Notably, Cs₂NaTbCl₆ exhibited a light yield of 42 200 photons per MeV, while retaining 98% of its initial radioluminescence intensity after 180 minutes of X-ray exposure, corresponding to a total radiation dose of approximately 86.4 Gy. Moreover, these materials achieved a spatial resolution of 10 lp mm⁻¹, even in flexible forms. The application of polydimethylsiloxane coating significantly enhanced the water resistance of the Cs₂NaLnCl₆ compounds and facilitated clear underwater X-ray imaging. This study highlights the promising potential of Ln-MHDPs for underwater X-ray imaging applications.