Halide perovskite (HP) nanocrystals (NCs) have recently shown great potential for X-ray detection and imaging. However, the practical application is still a long way to go with lots of technical requirements waiting to be fulfilled, including structure optimization, stability enhancement, and cost reduction. A design principle in this beginning stage is urgently needed but still lacking. Herein, with an "emitter-in-matrix" principle refined from commercial scintillators, CsPbBr3@Cs4PbBr6 with emissive CsPbBr3 NCs embedded inside solid-state Cs4PbBr6 host is brought to X-ray sensing and imaging. The Cs4PbBr6 matrix not only enhances the attenuation of X-rays but also dramatically improves the stability of CsPbBr3 NCs. A favorable optical design with the Cs4PbBr6 matrix being transparent to the emission from CsPbBr3 NCs enables efficient light output. As a result, stable and sensitive scintillation response to X-ray signals is demonstrated with superior linearity and ultrahigh time resolution.In order to show the huge potential for practical application, X-ray imaging using a large-area film (360 mm×240 mm) by blade-coating technique is carried out to obtain a high-quality image of human eye-invisible interior structures. In addition to the above advantages in optics, CsPbBr3@Cs4PbBr6 also enjoys facile solution synthesis with large scalability, excellent repeatability and low cost.

The elastic storage and release of mechanical energy has been key to many developments throughout the history of mankind. Resilience, absent hysteresis, has been an elusive goal to achieve, particularly at large deformations. Using a low‐crosslink‐density polyacrylamide hydrogel at 96% water content having hyperbranched silica nanoparticles (HBSPs) as the major junction points, a hysteresis‐free material is realized. The fatigue‐free characteristic of these composite hydrogels is evidenced by the invariance of the stress–strain curves at strain ratios of 4, even after 5000 cycles. At a strain ratio of 7, only a 1.3% hysteresis is observed. A markedly increased strain‐ratio‐at‐break of 11.5 is observed. The unique attributes of these resilient hydrogels are manifested in the high‐fidelity detection of dynamic deformations under cyclic loading over a broad range of frequencies, difficult to achieve with other materials.