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Stimuli‐responsive luminescent materials have attracted much research attention due to their wide application potential in various fields. Typically, the family of hydrated double perovskite A2MIIIX5·H2O shows unique emission color transformation between hydrated and dehydrated complexes, highlighting the application potential in advanced anti‐counterfeiting. Herein, two zero‐dimensional perovskites of Cs2YbCl5·H2O and Cs3YbCl6, are reported and broad‐band self‐trapped exciton recombination emission can be realized via external Sb3+ doping. Intriguingly, the Cs2YbCl5·H2O can be transformed to the dehydrated counterpart of Cs3YbCl6 through a facile methanol treatment at room temperature, leading to the emission color transformation from yellow to green. Notably, the green‐emissive Cs3YbCl6:Sb3+ delivers a high photoluminescence quantum yield of 67.3%. Leveraging the advantages of obvious methanol‐induced emission color transformation between Cs2YbCl5·H2O and Cs3YbCl6 at room temperature, Cs2YbCl5·H2O can be used in the field of high‐security‐level anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

The development of large‐area transparent organic‐inorganic hybrid metal halide (OIMH) scintillation screens is restricted by the anisotropic single‐crystal growth, numerous grain boundaries in polycrystalline wafers, and inhomogeneous dispersion in perovskite‐polymer composite films. The crystal‐glass phase transition of OIMH materials may provide a promising solution for the above significant challenges. Herein, a new class of transparent amorphous guanidinium‐based manganese bromide glasses, (DPG)2MnBr4 and (DOTG)2MnBr4 (DPG = 1,3‐diphenylguanidinium, DOTG = 1,3‐di‐o‐tolylguanidinium), are synthesized through a low‐temperature melt‐quenching process. The (DOTG)2MnBr4 shows impressive glass‐forming ability because of large viscosity (η) at the melting temperature (Tm) (η(Tm) = 3426 mPa·s) and small fragility index (m = 52.35), which can be a potential glass scintillator. The large‐area (e.g., 13 cm × 13 cm) transparent amorphous (DOTG)2MnBr4 glass scintillator shows high light transmittance of > 80%, a low detection limit of 237.3 nGy s−1 and high X‐ray imaging spatial resolution of 12 lp mm−1. Interestingly, the glass transition temperature of < 40 °C gives (DOTG)2MnBr4 glass unique thermoplastic properties, allowing it to conform to irregularly shaped objects and reduce the distortion in X‐ray imaging. [ABSTRACT FROM AUTHOR]

The current mainstream planar X‐ray imaging techniques face significant challenges for accurately capturing the internal structure of curved objects, since the variable distances between the curved objects and the flat‐panel scintillation screen cannot eliminate the distortion in X‐ray imaging. Though large‐area and transparent curved scintillation screens are much more desirable. Here, organic–inorganic hybrid Mn‐based single crystals ([CH3Ph3P]2MnX4, X = Cl, Br, I) exhibiting high photoluminescence quantum yield (PLQY) and low melting temperature have been employed to prepare transparent glass for X‐ray scintillation imaging application through a low‐temperature melting strategy. The [CH3Ph3P]2MnBr4‐glass shows high PLQY (47.8%), high‐resolution X‐ray imaging performance (12.3 lp mm−1), low limit of detection (25.33 nGy s−1), and impressive X‐ray irradiation stability (102 Gy). Furthermore, high‐contrast X‐ray imaging at a low dose (6.865 µGy per exposure, 14.5 times lower than the chest radiograph) is achieved. Based on the low glass transition temperature (Tg = 53.6 °C) and easy‐shapeable properties of [CH3Ph3P]2MnBr4‐glass scintillator, the large‐area curved scintillation screen with a series of sizes of Φ 2×4 – Φ 8×4 cm2 can be easily fabricated and show high X‐ray imaging quality. These findings provide a paradigm for future research in shapeable X‐ray scintillators, unlocking new possibilities for curved and 3D X‐ray imaging. [ABSTRACT FROM AUTHOR]

Single‐source white‐light emitters are highlighted with stable color and excellent color rendering ability, which can largely simplify the white‐light‐emitting‐diode (WLED) structure. All‐inorganic and lead‐free double perovskites have attracted extensive research interest and provide versatile doping sites to accommodate the extrinsic multi‐valent ions. Herein, the synthesis and tunable emission of Sb3+–Ln3+‐codoped Cs2NaYCl6 single crystals (SCs) is reported. Particularly, bright white‐light emission with a high photoluminescence quantum yield of 80.5% is yielded in 0.5%Sb3+–2%Tb3+–2%Sm3+‐codoped Cs2NaYCl6 SCs. Steady‐state photoluminescence (PL) and time‐resolved PL spectra are employed to reveal the energy transfer from Sb3+‐induced self‐trapped excitons to Ln3+ ions. Temperature‐dependent PL spectra further demonstrate that the fluorescence intensity ratio of band 657 to band 590 nm is highly dependent on the temperature, and the relative sensitivity reaches a maximum of up to 1.59% K−1 at 260 K. Moreover, the WLED based on 0.5%Sb3+‐2%Tb3+‐2%Sm3+‐codoped Cs2NaYCl6 SCs delivers a higher average color rendering index of 87 than 0.5%Sb3+‐0.8%Tb3+‐2.5%Ho3+‐codoped Cs2NaYCl6 (74.6). The outstanding white‐light‐emission performance together with the high temperature dependence of the fluorescence spectra confers Sb3+–Ln3+‐codoped Cs2NaYCl6 with huge application potential in solid‐state lighting and ratiometric optical thermometry. [ABSTRACT FROM AUTHOR]

Scintillators, which can convert high‐energy ionizing radiation (e.g., X‐ or γ‐rays) into ultraviolet‐visible light, have been widely applied in medical and industrial fields. Developing new scintillation materials with high performance and low cost is very desirable in order to address the growing application demands. Among them, single‐crystal scintillators of organic‐inorganic hybrid metal halides (OIMHs) have attracted much attention because of their excellent optical transparency, suppressed light scattering, and facile solution preparation methods. Herein, three new centimeter‐sized (2‐DMAP)2MnX4 (2‐DMAP+ = 2‐dimethylaminopyridinium, X = Cl, Br, I) single crystals with high crystal quality are synthesized via the solvent evaporation method. Benefiting from the high optical transparency and remarkable luminescence property, (2‐DMAP)2MnBr4 delivers a high X‐ray light yield of 22 000 photons MeV−1, a low limit of detection of 9.50 nGy s−1, and an excellent X‐ray imaging spatial resolution of 20–25 lp mm−1. Moreover, the regulation of single‐crystal thickness from 0.31 mm to 3.03 mm can be easily achieved via a simple solution post‐treatment method, which has a significant influence on the transmittance, spatial imaging resolution, and detection limit. This work demonstrates a promising single‐crystal scintillator for the application of high‐resolution X‐ray imaging with low preparation cost and tunable thickness. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) behaviors in metal halide perovskite and perovskite derivatives are rarely reported due to the absence of suitable TADF molecules that can serve as the A‐site cations. Herein, a series of novel donor‐π‐acceptor type of molecules are developed by adopting substituted phosphine and phosphonium as the electron donor and acceptor linked by the polarized π‐spacer. The prepared ((diphenylphosphaneyl)phenyl)diphenylphosphonium‐X (BzDPP‐X, X = counterions: Cl−, Br−, I−, NO3−, CH3COO− etc.) salts show bright emission in the visible range with TADF characteristics due to the strong intramolecular charge transfer (ICT). Benefiting from the spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, small singlet‐triplet energy splitting (ΔEST) is obtained, facilitating the reverse intersystem crossing process. It turns out that the emission of BzDPP‐X is dependent on the counter anions, and the counterions help to stabilize the ICT state. Intriguingly, the emission can be tuned by integrating metal‐halide units into the above phosphonium salt. Remarkably, the zinc‐based halide exhibits a higher photoluminescence quantum yield (36.2%) than the pure benzyl(2‐(diphenylphosphaneyl)phenyl)diphenylphosphonium bromide (26.9%). This work exemplifies an easy design concept and a facile synthetic method toward ionic luminescent materials. [ABSTRACT FROM AUTHOR]

Glass is a group of materials with appealing qualities, including simplicity in fabrication, durability, and high transparency, and they play a crucial role in the optics field. In this paper, a new organic–inorganic metal halide luminescent glass exhibiting >78 % transmittance at 506–800 nm range together with a high photoluminescence quantum yield (PLQY) of 28.5 % is reported through a low‐temperature melt‐quenching approach of pre‐synthesized (HTPP)2MnBr4 (HTPP=hexyltriphenylphosphonium) single crystal. Temperature‐dependent X‐ray diffraction, polarizing microscopy, and molecular dynamics simulations were combined to investigate the glass‐crystal interconversion process, revealing the disordered nature of the glassy state. Benefiting from the transparent nature, (HTPP)2MnBr4 glass yields an outstanding spatial resolution of 10 lp mm−1 for X‐ray imaging. The superb optical properties and facility of large‐scale fabrication distinguish the organic–inorganic metal halide glass as a highly promising class of materials for optical devices. [ABSTRACT FROM AUTHOR]

Anti‐counterfeiting has become a serious issue around the global world; fluorescence‐based tags are praised for the low‐cost and facile decryption process. However, the high‐level anti‐counterfeiting application requires incorporating multifunctional luminescent materials with response to different excitation sources. Herein, a dimeric Cu(I)‐halide‐clusters‐assembled single‐crystal (AEP)2Cu2I6·2I·2H2O (AEP = N‐aminoethylpiperazinium) concerning a high down‐conversion photoluminescence quantum yield (PLQY) value of near unity is reported (λex = 305 nm), which can also be activated by the near‐infrared light and X‐ray. The ultrafast spectroscopy and density functional theory calculations reveal that the broad‐band emission originates from the recombination of self‐trapped excitons. Remarkably, the high PLQY and excellent attenuation capability for X‐ray confers an outstanding light yield of 55 650 photons MeV−1 to (AEP)2Cu2I6·2I·2H2O, which is 5.25 times higher than the standard bismuth germaniumoxide scintillator. Such multi‐light‐stimulus response endows (AEP)2Cu2I6·2I·2H2O with great application potential in anti‐counterfeiting, solid‐state lighting devices, and digital radiography. [ABSTRACT FROM AUTHOR]

Although multiple emissive materials are of great research interest due to their great potential in a variety of applications, it is still challenging to prepare highly luminescent color‐tunable phosphors. Herein, the authors report a series of Pb−Sn alloyed single crystals, (C10NH22)2Pb1−xSnxBr4 (x = 0 to 1), that are equipped with two independent self‐trapped excitons (STEs) emitters. Multicolor luminescent output from blue to red and white light can be obtained by tailoring the composition, excitation wavelength, temperature, or time gating. More importantly, the synergistic effect between PbBr42− and SnBr42− enables (C10NH22)2Pb1−xSnxBr4 to have an extremely high luminescent efficiency up to near unity and remarkably extends stability in ambient air, significantly outperforming the monometallic (C10NH22)2PbBr4 and (C10NH22)2SnBr4. As an encouraging result of the richly endowed emission property and robust stability, (C10NH22)2Pb1−xSnxBr4 is further employed in multifunctional applications including the luminescent radiometric thermometer, white light emitter, and high‐security anti‐counterfeit materials. [ABSTRACT FROM AUTHOR]

Organic scintillators are praised for their abundant element reserves, facile preparation procedures, and rich structures. However, the weak X‐ray attenuation ability and low exciton utilization efficiency result in unsatisfactory scintillation performance. Herein, a new family of highly efficient organic phosphonium halide salts with thermally activated delayed fluorescence (TADF) are designed by innovatively adopting quaternary phosphonium as the electron acceptor, while dimethylamine group and halide anions (I−) serve as the electron donor. The prepared butyl(2‐[2‐(dimethylamino)phenyl]phenyl)diphenylphosphonium iodide (C4‐I) exhibits bright blue emission and an ultra‐high photoluminescence quantum yield (PLQY) of 100 %. Efficient charge transfer is realized through the unique n‐π and anion‐π stacking in solid‐state C4‐I. Photophysical studies of C4‐I suggest that the incorporation of I accounts for high intersystem crossing rate (kISC) and reverse intersystem crossing rate (kRISC), suppressing the intrinsic prompt fluorescence and enabling near‐pure TADF emission at room temperature. Benefitting from the large Stokes shift, high PLQY, efficient exciton utilization, and remarkable X‐ray attenuation ability endowed by I, C4‐I delivers an outstanding light yield of 80721 photons/MeV and a low limit of detection (LoD) of 22.79 nGy ⋅ s−1. This work would provide a rational design concept and open up an appealing road for developing efficient organic scintillators with tunable emission, strong X‐ray attenuation ability, and excellent scintillator performance. [ABSTRACT FROM AUTHOR]