Colloidal Synthesis of Hollow Double Perovskite Nanocrystals and Their Applications in X-ray Imaging

Rare earth-based halide double perovskites are regarded as an emerging class of X-ray scintillation materials. However, the majority of related scintillator applications are still focused on single crystal and powder systems; the application of nanocrystal (NC) scintillators is rarely reported. Here, we present the synthesis of high-purity Cs₂NaTbCl₆ NCs by an improved hot-injection method. Interestingly, hollow Cs₂NaTbCl₆ NCs are observed, the monitoring of the growth process indicates that micrometer-sized NaCl is the initial product, and then the NaCl would convert into Cs₂NaTbCl₆ NCs through the diffusion of Cs⁺ and Tb³⁺ into NaCl lattice, and the faster outward diffusion of Na⁺ results in the formation of hollow NCs. The double perovskite NCs exhibit green light emission, and the photoluminescence intensity can be significantly enhanced through Ce³⁺ doping. In particular, the Cs₂NaTbCl₆:5%Ce³⁺ scintillator exhibits a linear response and a low detection limit of 79.09 nGy/s when exposed to X-rays. Furthermore, a flexible scintillator film for X-ray imaging is prepared by mixing NCs with polymer, showing a high spatial resolution imaging capability of 10 lp/mm. This work provides a new strategy for hollow perovskite NCs and may shed light on the synthesis of related hollow NCs and their applications in X-ray detection.