Search

Ultra‐broadband near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) have great application prospects in research and industrial fields. However, simultaneously achieving highly efficient and ultra‐broad NIR emission in phosphor material remains a challenge. Herein, an ultra‐broadband NIR emission in the range of 800–1200 nm with ultra‐high emission efficiency of up to 64.2% is first achieved by substituting the Sc3+ site in Cs2NaScCl6 perovskite single‐crystal with a Cr3+ ion. By combining the experimental results with first‐principles calculations, an efficient charge transfer sensitization process from host to Cr3+ is found to be the fundamental reason for the ultra‐high NIR emission efficiency. Benefiting from the excellent efficiency and superior chemical resistance to heat and UV radiation, an ultra‐broadband NIR pc‐LED made of this phosphor demonstrates great potential in biomedical imaging, nondestructive testing, and night‐vision devices. [ABSTRACT FROM AUTHOR]

Self-trapped excitons (STEs) emission from halide perovskites with strong exciton-phonon coupling has attracted considerable attention due to the widespread application in optoelectronic devices. Nevertheless, the in-depth understanding of the relationship between exciton-phonon coupling and luminescence intensity remains incomplete. Herein, a doping-enhanced exciton-phonon coupling effect is observed in Cs3Cu2I5 nanocrystals (NCs), which leads to a remarkable increasement of their STEs emission efficiency. Mechanism study shows that the hetero-valent substitution of Cu+ with alkaline-earth metal ions (AE2+) causes a greater degree of Jahn–Teller distortion between the ground state and excited state structures of [Cu2I5]3− clusters as evidenced by our spectral analysis and first-principles calculations. As a consequence, an X-ray detector based on these Cs3Cu2I5:AE NCs delivers an X-ray imaging resolution of up to 10 lp·mm−1 and a low detection limit of 0.37 µGyair·s−1, disclosing the potential of doping-enhanced exciton-phonon coupling effect in improving STEs-emission and practical application for X-ray imaging. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials hold great promise as next‐generation efficient emitters due to their theoretical 100% internal quantum efficiency. However, such an intriguing photophysical mechanism is extremely rare in perovskites or their derivatives. Herein, the colloidal synthesis of two‐dimensional CsAgCl2 nanocrystals (NCs) with typical TADF feature is reported first. The TADF mechanism is investigated in detail by combining first‐principles calculations with experimental results, including temperature‐dependent spectral analysis and fs‐transient absorption spectra. A small singlet−triplet state splitting energy (0.082 eV) and a large spatial separation of charge density |Ψ|2 of valence band maximum and conduction band minimum are observed, which are prerequisites for TADF. Moreover, these CsAgCl2 NCs deliver an ultralow X‐ray detection limit of 170.5 nGyair s−1 and a high imaging resolution of 11.5 lp mm−1, much superior to the commercial scintillators. [ABSTRACT FROM AUTHOR]

Zero‐dimensional (0D) copper‐based perovskite‐derivative nano‐scintillators (NSs), as a promising non‐toxic alternative to lead‐based halide perovskite, have shown great potential in flexible X‐ray detection and imaging. However, their practical applications are still impeded by low X‐ray imaging resolution associated with inadequate radioluminescence (RL) and poor environmental stability. Herein, for the first time a simple but valid Mn2+‐activation strategy is proposed to highly enhance the RL and stability of 0D Cs3Cu2I5 NSs, where the Mn2+ ions are embedded into the highly localized [Cu2I5]3− units by utilizing a modified hot‐injection method. As such, a newly emerged emission band of Mn2+ ion centered at ≈562 nm coupled with much improved intrinsic self‐trapped excitons (STE) emission of the 0D Cs3Cu2I5 host peaking at ≈445 nm can be achieved in these resultant Mn2+‐activated 0D Cs3Cu2I5 NSs, thereby delivering a light yield of 71 000 photons MeV−1 that is much superior to their lead‐based perovskite counterparts and commercial scintillators. As a consequence, X‐ray detectors made of these Mn2+‐activated NSs implement an ultrahigh X‐ray imaging resolution of 16.2 line pairs mm−1 and an ultra‐low detection limit of 127.5 nGyair s−1, highlighting their potential as promising candidates for flexible X‐ray detection and imaging. [ABSTRACT FROM AUTHOR]

Inherent "soft" ionic lattice nature of halide perovskite quantum dots (QDs), triggered by the weak Pb-X (X=Cl, Br, I) bond, is recognized as the primary culprit for their serious instability. A promising way is to construct exceedingly strong ionic interaction inside the QDs and increase their crystal cohesive energy by substituting the interior X - with highly electronegative F - , however, which is challenging and hitherto remains unreported. Here, a "whole-body" fluorination strategy is proposed for strengthening the interior bonding architecture of QDs, wherein the F - are uniformly distributed throughout the whole nanocrystal encompassing both the interior lattice and surface, successfully stabilizing their "soft" crystal lattice and passivating surface defects. This approach effectively mitigates their intrinsic instability issues including light-induced phase segregation. As a result, light-emitting devices based on these QDs exhibit exceptional efficiency and remarkable stability., (© 2024 Wiley-VCH GmbH.)