Transparent nanocomposites have attracted considerable attention in many areas including X-ray imaging, wearable electronics, and volumetric display. However, both the transparency and the flexibility were largely jeopardized by the loading content of functional nanoparticles (NPs), posing a major challenge to material engineering. Herein, an ultra-highloading-ceramic nanocomposite film was fabricated by a bladecoating technique. The film exhibited a high transparency over ∼89% in the whole visible region even with a fluoride-ceramic content up to ∼83 wt %. Based on a real-time investigation on the formation process of the film, the refractive-index difference between the nanoparticles and matrix was identified as the dominating factor to transparency. The transmittance spectra based on Rayleigh scattering theory were simulated to screen both nanoparticle radius and loading content, leading to the discovery of a transparency zone for film making. As a proof-ofconcept experiment, the transparent film was used as an X-ray scintillation screen, which exhibited a comparable light yield to that of LYSO owing to the mitigated self-absorption effect. The homemade imager demonstrated a spatial resolution of 122 lp/mm, representing a record resolution of 4.1 μm for laboratory X-ray photography. Our work not only provided an experimental procedure to make high-loading functional films but also demonstrated a theoretical model to guide the search for gradients of transparent composites.

Trap tuning has been viewed as the major tool to improve the afterglow performance of various phosphors. Herein, we report a trap-tuning strategy involving alkali metal ions of Li+ and...

Lanthanide‐doped halide perovskite has emerged as a promising phosphor for multimode luminescence. Here, a chloride‐based perovskite single crystal is reported, namely Cs2NaInCl6:Yb3+,Er3+, that is grown in a hydrothermal reactor. The as‐grown crystals feature two distinct luminescence behaviors under UV and 980 nm laser excitation, respectively. Under UV lamp excitation, the crystal shows a multicolor emission of sharp bands at 448, 550, and 660 nm, covering a wide color gamut in CIE diagram. In stark contrast, the crystal under 980 nm excitation exhibits a pure green upconversion with a green‐to‐red ratio up to 211. The universal green dominance is further demonstrated in many chlorides, including Cs2AgInCl6, Cs2NaBiCl6, and Cs2AgBiCl6. The strong green upconversion is used for optical thermometry, which demonstrates an unprecedented sensitivity up to 9.3% K−1 at the low temperature end. The work introduces a kind of new hosts for single‐band upconversion luminescence, opening up many possibilities in areas such as low‐threshold laser and pure‐green color converter.

Cs3Cu2Cl5 has attracted great attention in many photonic applications owing to its high photoluminescence quantum yield (PL QY), nontoxicity, and large Stokes shift. However, its labile nature to air and single-color emission have limited its practical use in display-related applications. In this work, a single crystal of Cs3Cu2Cl5 was grown with a user-friendly Cu2+ precursor. To tune the emission color and stability, the anion-exchange reaction was employed with trace amounts of I ions. The anion-exchanged crystals not only enabled a fine color tuning from sky-blue to emerald-green but also dramatically improved the chemical stability of Cs3Cu2Cl5. Microscopic imaging of an individual crystal flake demonstrated a uniform emission of cross section, which was quite different from conventional core/shell structures. Importantly, the anion-exchanged crystals retained a high PL QY up to 98%. Our work brings insights into the manipulation of self-trapped excitons, opening many avenues for stable photoelectric devices.