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Lanthanide‐based NIR‐II‐emitting materials (1000–1700 nm) show promise for optoelectronic devices, phototherapy, and bioimaging. However, one major bottleneck to prevent their widespread use lies in low quantum efficiencies, which are significantly constrained by various quenching effects. Here, a highly oriented (222) facet is achieved via facet engineering for Cs2NaErCl6 double perovskites, enabling near‐complete suppression of NIR‐II luminescence quenching. The optimally (222)‐oriented Cs2Ag0.10Na0.90ErCl6 microcrystals emit Er3+ 1540 nm light with unprecedented high quantum efficiencies of 90 ± 6% under 379 nm UV excitation (ultralarge Stokes shift >1000 nm), and a record near‐unity quantum yield of 98.6% is also obtained for (222)‐based Cs2NaYb0.40Er0.60Cl6 microcrystallites under 980 nm excitation. With combined experimental and theoretical studies, the underlying mechanism of facet‐dependent Er3+ 1540 nm emissions is revealed, which can contribute to surface asymmetry‐induced breakdown of parity‐forbidden transition and suppression of undesired non‐radiative processes. Further, the role of surface quenching is reexamined by molecular dynamics based on two facets, highlighting the drastic two‐phonon coupling effect of a hydroxyl group to 4I13/2 level of Er3+. Surface‐functionalized facets will provide new insights for tunable luminescence in double perovskites, and open up a new avenue for developing highly efficient NIR‐II emitters toward broad applications. The preferred (222) facet in Cs2NaErCl6 double perovskite is favorable for Er3+ 1540 nm emission with a record quantum yield of 98.6% under 980 nm excitation, which is useful for surface modification. These findings suggest facet engineering is a new way for realizing highly efficient Er3+‐based NIR‐II emitters toward broad applications.

In photoluminescence spectroscopy experiments, the interaction mode of the polymer membrane Nafion with various amino-acids was studied. The experiments were performed with physiological NaCl solutions prepared in an ordinary water (the deuterium content is 157 ± 1 ppm) and also in deuterium-depleted water (the deuterium content is ≤1 ppm). These studies were motivated by the fact that when Nafion swells in ordinary water, the polymer fibers are effectively “unwound” into the liquid bulk, while in the case of deuterium-depleted water, the unwinding effect is missing. In addition, polymer fibers, unwound into the liquid bulk, are similar to the extracellular matrix (glycocalyx) on the cell membrane surface. It is of interest to clarify the role of unwound fibers in the interaction of amino-acids with the polymer membrane surface. It turned out that the interaction of amino-acids with the membrane surface gives rise to the effects of quenching luminescence from the luminescence centers. We first observed various dynamic regimes arising upon swelling the Nafion membrane in amino-acid suspension with various isotopic content, including triggering effects, which is similar to the processes in the logical gates of computers.

Perovskite light-emitting diodes (LEDs) have attracted broad attention due to their rapidly increasing external quantum efficiencies (EQEs) 1 – 15 . However, most high EQEs of perovskite LEDs are reported at low current densities (<1 mA cm −2 ) and low brightness. Decrease in efficiency and rapid degradation at high brightness inhibit their practical applications. Here, we demonstrate perovskite LEDs with exceptional performance at high brightness, achieved by the introduction of a multifunctional molecule that simultaneously removes non-radiative regions in the perovskite films and suppresses luminescence quenching of perovskites at the interface with charge-transport layers. The resulting LEDs emit near-infrared light at 800 nm, show a peak EQE of 23.8% at 33 mA cm −2 and retain EQEs more than 10% at high current densities of up to 1,000 mA cm −2 . In pulsed operation, they retain EQE of 16% at an ultrahigh current density of 4,000 mA cm −2 , along with a high radiance of more than 3,200 W s −1  m −2 . Notably, an operational half-lifetime of 32 h at an initial radiance of 107 W s −1  m −2 has been achieved, representing the best stability for perovskite LEDs having EQEs exceeding 20% at high brightness levels. The demonstration of efficient and stable perovskite LEDs at high brightness is an important step towards commercialization and opens up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers. Perovskite LEDs with exceptional performance at high brightness are demonstrated achieving an operational half-lifetime of 32 hours, an important step towards commercialization opening up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers.

Efficiency roll-off is a major issue for most types of light-emitting diodes (LEDs), and its origins remain controversial. Here we present investigations of the efficiency roll-off in perovskite LEDs based on two-dimensional layered perovskites. By simultaneously measuring electroluminescence and photoluminescence on a working device, supported by transient photoluminescence decay measurements, we conclude that the efficiency roll-off in perovskite LEDs is mainly due to luminescence quenching which is likely caused by non-radiative Auger recombination. This detrimental effect can be suppressed by increasing the width of quantum wells, which can be easily realized in the layered perovskites by tuning the ratio of large and small organic cations in the precursor solution. This approach leads to the realization of a perovskite LED with a record external quantum efficiency of 12.7%, and the efficiency remains to be high, at approximately 10%, under a high current density of 500 mA cm −2 . Large drop in efficiency at high brightness has been holding back the development of various light-emitting diodes including halide perovskite. Here Zou et al. achieve high quantum efficiency of 10% under a high current density of 500 mA cm −2 in perovskite-based diodes by reducing luminescence quenching.

The synthesis of dynamic chiral lanthanide complex emitters has always been difficult. Herein, we report three pairs of dynamic chiral Eu III complex emitters ( R/S -Eu-R-1 , R = Et/Me; R/S -Eu-Et-2 ) with aggregation-induced emission. In the molecular state, these Eu III complexes have almost no obvious emission, while in the aggregate state, they greatly enhance the Eu III emission through restriction of intramolecular rotation and restriction of intramolecular vibration. The asymmetry factor and the circularly polarized luminescence brightness are as high as 0.64 ( 5 D 0  →  7 F 1 ) and 2429 M −1 cm −1 of R -Eu-Et-1 , achieving a rare double improvement. R -Eu-Et-1/2 exhibit excellent sensing properties for low concentrations of Cu II ions, and their detection limits are as low as 2.55 and 4.44 nM, respectively. Dynamic Eu III complexes are constructed by using chiral ligands with rotor structures or vibration units, an approach that opens a door for the construction of dynamic chiral luminescent materials. Chiral luminescent materials are of increasing interest in various applications, but achieving a desirable balance of properties can be challenging. Here, the authors report the development of Eu-based complexes with chiral luminescence and aggregation induced emission.

Organocatalysis—catalysis mediated by small chiral organic molecules—is a powerful technology for enantioselective synthesis, and has extensive applications in traditional ionic, two-electron-pair reactivity domains. Recently, organocatalysis has been successfully combined with photochemical reactivity to unlock previously inaccessible reaction pathways, thereby creating new synthetic opportunities. Here we describe the historical context, scientific reasoning and landmark discoveries that were essential in expanding the functions of organocatalysis to include one-electron-mediated chemistry and excited-state reactivity. This Review discusses recent developments in the combination of organocatalysis and photochemistry for the activation of molecules, which has enabled previously inaccessible reaction pathways and influenced many fields of chemical research. The rise of organocatalysis Organocatalysis uses small, chiral organic molecules as catalysts and has been widely applied to asymmetric reactions in the past few decades. In this Review, Mattia Silvi and Paolo Melchiorre look at how, in combination with photochemical reactivity, the field has moved from traditional two-electron-pair reactivity to include one-electron and excited-state chemistry. The merger of these two fields has expanded the scope of asymmetric organocatalysis substantially, providing access to previously unavailable synthetic prospects, and this combination shows promise for developing new stereocontrolled catalytic processes.

Lighting accounts for one-fifth of global electricity consumption 1 . Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties 2 , 3 ; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl 6 octahedron in the excited state. By alloying sodium cations into Cs 2 AgInCl 6 , we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor 4 . This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs 2 AgInCl 6 . The optimally alloyed Cs 2 (Ag 0.60 Na 0.40 )InCl 6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies. After alloying with metal cations, a lead-free halide double perovskite shows stable performance and remarkably efficient white-light emission, with possible applications in lighting and display technologies.

Dynamic control of multi-photon upconversion with rich and tunable emission colors is stimulating extensive interest in both fundamental research and frontier applications of lanthanide based materials. However, manipulating photochromic upconversion towards color-switchable emissions of a single lanthanide emitter is still challenging. Here, we report a conceptual model to realize the spatiotemporal control of upconversion dynamics and photochromic evolution of Er 3+ through interfacial energy transfer (IET) in a core-shell nanostructure. The design of Yb sublattice sensitization interlayer, instead of regular Yb 3+ doping, is able to raise the absorption capability of excitation energy and enhance the upconversion. We find that a nanoscale spatial manipulation of interfacial interactions between Er and Yb sublattices can further contribute to upconversion. Moreover, the red/green color-switchable upconversion of Er 3+ is achieved through using the temporal modulation ways of non-steady-state excitation and time-gating technique. Our results allow for versatile designs and dynamic management of emission colors from luminescent materials and provide more chances for their frontier photonic applications such as optical anti-counterfeiting and speed monitoring. Achieving spatiotemporal control of photochromic upconversion from a single lanthanide emitter remains challenging. Here, the authors present a conceptual model enabling such control of Er 3+ photochromic upconversion via interfacial energy transfer in a core-shell nanostructure.

In vivo fluorescence imaging in the near-infrared region between 1500–1700 nm (NIR-IIb window) affords high spatial resolution, deep-tissue penetration, and diminished auto-fluorescence due to the suppressed scattering of long-wavelength photons and large fluorophore Stokes shifts. However, very few NIR-IIb fluorescent probes exist currently. Here, we report the synthesis of a down-conversion luminescent rare-earth nanocrystal with cerium doping (Er/Ce co-doped NaYbF 4 nanocrystal core with an inert NaYF 4 shell). Ce doping is found to suppress the up-conversion pathway while boosting down-conversion by ~9-fold to produce bright 1550 nm luminescence under 980 nm excitation. Optimization of the inert shell coating surrounding the core and hydrophilic surface functionalization minimize the luminescence quenching effect by water. The resulting biocompatible, bright 1550 nm emitting nanoparticles enable fast in vivo imaging of blood vasculature in the mouse brain and hindlimb in the NIR-IIb window with short exposure time of 20 ms for rare-earth based probes. Fluorescence imaging in the near-infrared window between 1500–1700 nm (NIR-IIb window) offers superior spatial resolution and tissue penetration depth, but few NIR-IIb probes exist. Here, the authors synthesize rare earth down-converting nanocrystals as promising fluorescent probes for in vivo imaging in this spectral region.

Red-emitting Mn4+-doped fluorides are a promising class of materials to improve the color rendering and luminous efficacy of white light-emitting diodes (w-LEDs). For w-LEDs, the luminescence quenching temperature is very important, but surprisingly no systematic research has been conducted to understand the mechanism for thermal quenching in Mn4+-doped fluorides. Furthermore, concentration quenching of the Mn4+ luminescence can be an issue but detailed investigations are lacking. In this work, we study thermal quenching and concentration quenching in Mn4+-doped fluorides by measuring luminescence spectra and decay curves of K2TiF6:Mn4+ between 4 and 600 K and for Mn4+ concentrations from 0.01% to 15.7%. Temperature-dependent measurements on K2TiF6:Mn4+ and other Mn4+-doped phosphors show that quenching occurs through thermally activated crossover between the 4T2 excited state and 4A2 ground state. The quenching temperature can be optimized by designing host lattices in which Mn4+ has a high 4T2 state energy. Concentration-dependent studies reveal that concentration quenching effects are limited in K2TiF6:Mn4+ up to 5% Mn4+. This is important, as high Mn4+ concentrations are required for sufficient absorption of blue LED light in the parity-forbidden Mn4+d–d transitions. At even higher Mn4+ concentrations (>10%), the quantum efficiency decreases, mostly due to direct energy transfer to quenching sites (defects and impurity ions). Optimization of the synthesis to reduce quenchers is crucial for developing more efficient highly absorbing Mn4+ phosphors. The present systematic study provides detailed insights into temperature and concentration quenching of Mn4+ emission and can be used to realize superior narrow-band red Mn4+ phosphors for w-LEDs.