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Zero-dimensional (0D) hybrid metal halides (HMHs) have emerged as a promising platform for exploring excitation-dependent multicolor luminescent materials owing to their diverse crystal structures and chemical compositions. Nevertheless, understanding the mechanism behind excitation-dependent emissions (EDEs) in 0D HMHs and achieving precise modulation remains challenging. In this work, the delicate regulations on the EDE of 0D (DMEDABr)4SnBr3I3 (DMEDA: N, N′-dimethylethylenediamine) with mixed halogens are achieved under low temperature and high pressure, respectively. The inhomogeneous halogen occupation at the atomic scale leads to the formation of Br-rich and I-rich SnX6 (X = Br, I) octahedra, which act as distinct luminescent centers upon photoexcitation. At low temperatures, the narrowed photoluminescence spectra could distinguish the individual emissions from different luminescent centers, resulting in a pronounced EDE of (DMEDABr)4SnBr3I3. In addition, the contraction and distortion of the luminescent SnX6 (X = Br, I) centers at high pressure further result in different degrees of emission shifts, giving rise to the gradual emergence and disappearance of EDE. This work elucidates the underlying mechanism of EDE in 0D HMHs and highlights the crucial role of halogens in determining the optical properties of metal halides. [ABSTRACT FROM AUTHOR]

The rich and unique energy level structure arising from 4fn inner shell configuration of trivalent lanthanide ions (Ln3+) renders them highly attractive for light‐emitting applications. Currently, research primarily focuses on Ln3+ doping in either traditional garnets or the recently developed perovskite phosphors. However, there have been few reports on stable phosphors crystallized with pure lanthanide elements. Herein, a universal solution‐based route to eight Ln3+‐based metal halides from the organic‐inorganic A4LnX7 family is described, where A+ = 4,4‐difluoropiperidinium (DFPD+), Ln3+ = Nd3+, Eu3+, Ho3+, Sm3+, Tm3+, Tb3+, Yb3+, Er3+, and X− = Cl−, Br−. Visible photoluminescence (PL) is observed from Tb3+‐, Eu3+‐, Ho3+‐, and Sm3+‐based compounds with Tb and Eu compositions exhibiting high PL quantum yields of 90–100%; Nd3+‐, Tm3+‐, Yb3+‐, and Er3+‐based crystals show fascinating near‐infrared emission. Light‐emitting diodes (LEDs) fabricated with (DFPD)4TbCl7 yield characteristic emission of Tb3+, representing the first demonstration of electroluminescence from these organic‐inorganic Ln3+‐based metal halides. Moreover, these materials exhibit distinct excitation wavelength‐dependent emission after alloying with different Ln3+ ions, making them interesting for multicolor display and multilevel information encryption applications. It is foreseen that this study will open up the way to a possible design of robust optoelectronic devices based on lanthanide metal halides. [ABSTRACT FROM AUTHOR]

Realizing ultra‐efficient broadband near‐infrared (NIR) luminescence, especially under blue light excitation, remains an enormous challenge in lead‐free metal halides. Herein, the efficient NIR emission under blue light excitation is achieved in Sb3+‐doped 0D (ETPP)2ZnCl4xBr4‐4x (x = 0–1) (ETPP+ = (Ethyl)triphenylphosphonium) through coordination structure modulation and halogen substitution. Compared with the visible light emission of Sb(III)‐based compounds, the emission in Sb3+‐doped (ETPP)2ZnCl4xBr4‐4x shifts to the NIR region due to the large excited state lattice distortion. Parallelly, the excitation bands gradually shift from 376 to 450 nm as Br gradually replaces Cl, and the emission bands can further shift from 702 to 763 nm. Thus, the broadband NIR emission at 763 nm with a record luminous efficiency of 55.4% under 450 nm excitation can be achieved in Sb3+‐doped compounds. Moreover, the large‐scale synthesis technique of Sb3+‐doped (ETPP)2ZnBr4: NIR phosphors at room temperature is further developed and this compound exhibits impressive thermal and chemical‐stabilities. Finally, a high‐performance NIR light‐emitting‐diode is fabricated by combining a commercial blue chip and (ETPP)2ZnBr4:10%Sb3+ phosphors, which shows the most advanced photoelectric efficiency (17.8%) and output power (67.7 mW) in lead‐free metal halides. Thus, the as‐fabricated device is further demonstrated in the applications of night vision and biomedical imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rich solvatochromic and thermochromic behavior of TPB offers new avenues for smart materials, etc. • TPB with narrowband emission is achieved, demonstrating the potential of TPB for wide colour gamut display applications. • In addition to the inorganic framework, solvent molecules also affect the luminescent properties of metal halides. The luminescent properties of metal halides are usually considered to be determined by the inorganic framework. In this work, we propose that the luminescent properties of metal halides are determined by both the inorganic framework and the solvent [Denoted as (inorganic framework + n· solvent molecules), n = 0, 1, 2...] through the abundant solvatochromic or thermochromic effect of tetrabutylammonium lead bromides [TPB, T = TBA (tetrabutylammonium), P = Pb (lead), B = Br (bromide)] containing water (H 2 O) and ethanol (EtOH). One-dimensional (1D) TPB can form ligands of [[Pb 5 Br 18 ]8− + 2H 2 O (H) ], [[Pb 5 Br 18 ]8− + 2H 2 O (H) + 2H 2 O] and [[Pb 5 Br 18 ]8− + 2EtOH] by solvent or heat treatment has completely different luminescent properties resulting from different solvents. They exhibit broad spectral emission due to strong electron-phonon coupling, as do other 1D metal halides. However, the 1D TPB containing only [[Pb 5 Br 18 ]8− achieves extremely rare narrow-band green emission, with full width at half maximum (FWHM) of 21 nm at room temperature and 8 nm at low temperature, color gamut covers 95 % of the International Telecommunication Union recommendation 2020 standard. This work provides new guidance for the modulation of photophysical properties of metal halides, as well as new materials for the display and smart materials fields. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid Ge(II)‐based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics. However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application. In addressing these issues, a breakthrough in the large‐scale production of Sb3+‐doped Ge(IV)‐based metal halide (C13H14N3)2GeCl6 phosphors at room temperature through a straightforward solution method is presented. The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 ± 0.06% the highest among Ge(IV)‐based metal halides. Notably, the introduction of Sb3+ induces the formation of Jahn–Teller‐like self‐trapped excitons in [SbCl6]3− species, attributable to lattice distortion and strong electron–phonon coupling. Consequently, Sb3+‐doped (C13H14N3)2GeCl6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs). Furthermore, the Sb3+‐doped compound exhibits commendable chemical‐ and photostability, prompting exploration in applications such as white light‐emitting diodes and latent fingerprint detection. This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application. [ABSTRACT FROM AUTHOR]

Organic–inorganic metal halides (OIMHs) have strengthened the development of triplet-state emission materials due to their excellent luminescence performance. Due to the inherent toxicity of lead (Pb) significantly limiting its further advancement, numerous studies have been conducted to regulate triplet-state emission of non-Pb OIMHs, and several feasible strategies have been proposed. However, most of the non-Pb OIMHs reported have a relatively short lifetime or a low luminescence efficiency, not in favor of their application. In this review, we provide a summary of recent reports on the regulation of triplet-state emissions in non-Pb OIMHs to provide benefits for the design of innovative luminescent materials. Our focus is primarily on exploring the internal and external factors that influence the triplet-state emission. Starting from the luminescence mechanism, the current strategies for regulating triplet-state emissions are summarized. Moreover, by manipulating these strategies, it becomes feasible to achieve triplet-state emissions that span a range of colors from blue to red, and even extend into the near-infrared spectrum with high luminescence efficiency, while also increasing their lifetimes. This review not only provides fresh insights into the advancement of triplet-state emissions in OIMHs but also integrates experimental and theoretical perspectives to illuminate the trajectory of future research endeavors. [ABSTRACT FROM AUTHOR]

Low‐dimensional metal halides (LDMHs) represent a promising class of materials in various luminescent applications because of their self‐trapped exciton (STE) emissions with unique properties such as broad luminescence spectra, large Stokes shift, and high color rendition. LDMHs at the molecular level can be constructed, including 2D layers, 1D chains, and 0D clusters assembled by polyhedra units, all of which exhibit significantly different luminescence properties from 3D MHs. The dimensional regulation of LDMHs has been explored for years, including the choice of organic cations, modulating electron‐phonon coupling effect, and adding external temperature and pressure. Herein, this review discusses the synergy between structural engineering and solvent effects for LDMHs, including the emission mechanisms for LDMHs and the roles solvent molecules play in regulating the dimensions. In addition, challenges and opportunities for LDMHs are discussed to shed light on the future development of novel materials with multifunctional optical properties suitable for practical applications. [ABSTRACT FROM AUTHOR]

The rich and unique energy level structure arising from 4fn inner shell configuration of trivalent lanthanide ions (Ln3+) renders them highly attractive for light‐emitting applications. Currently, research primarily focuses on Ln3+ doping in either traditional garnets or the recently developed perovskite phosphors. However, there have been few reports on stable phosphors crystallized with pure lanthanide elements. Herein, a universal solution‐based route to eight Ln3+‐based metal halides from the organic‐inorganic A4LnX7 family is described, where A+ = 4,4‐difluoropiperidinium (DFPD+), Ln3+ = Nd3+, Eu3+, Ho3+, Sm3+, Tm3+, Tb3+, Yb3+, Er3+, and X− = Cl−, Br−. Visible photoluminescence (PL) is observed from Tb3+‐, Eu3+‐, Ho3+‐, and Sm3+‐based compounds with Tb and Eu compositions exhibiting high PL quantum yields of 90–100%; Nd3+‐, Tm3+‐, Yb3+‐, and Er3+‐based crystals show fascinating near‐infrared emission. Light‐emitting diodes (LEDs) fabricated with (DFPD)4TbCl7 yield characteristic emission of Tb3+, representing the first demonstration of electroluminescence from these organic‐inorganic Ln3+‐based metal halides. Moreover, these materials exhibit distinct excitation wavelength‐dependent emission after alloying with different Ln3+ ions, making them interesting for multicolor display and multilevel information encryption applications. It is foreseen that this study will open up the way to a possible design of robust optoelectronic devices based on lanthanide metal halides.

Phonon-assisted upconversion process is one of the important means to generate upconversion photoluminescence (UCPL), and has important applications in laser refrigeration and other fields. However, until now, the studies on UCPL behavior are still insufficient. Herein, this work synthesizes a series of Mn-doped two-dimensional hybrid metal halide (2D HMH) thin films and investigates their optical properties using various spectral techniques. Raman spectroscopic measurement confirms that Mn-doping is achieved via interstitial doping rather than Pb-substitution. By the measurement of the temperature-dependent PL spectrum, it is found that Mn-doping will weaken the thermal expansion effect of 2D HMHs, but will enhance the electron–phonon coupling strength. More importantly, both two-photon-excited and phonon-assisted UCPL are observed in Mn-doped 2D HMHs, with an extremely large phonon-assisted energy gain (approximately 500 meV). Our experimental results are of significance for designing phonon-assisted UCPL materials and expanding their applications. [ABSTRACT FROM AUTHOR]

Stimuli-responsive photoluminescent (PL) materials have attracted considerable attention in recent years owing to their potential applications in anti-counterfeiting, information encryption, and sensing. Further investigations of the transformation mechanism and potential applications of stimulus-responsive PL materials are considerably important. In the current study, an organic-inorganic metal halide, C9H15N3SbCl5 ([C9H13N3]2+ is a 1-(2-pyridyl) piperazine cation) is obtained, which exhibits a 0D structure with P-1 space group. At room temperature, when excited by UV light, the C9H15N3SbCl5 single crystals exhibit unimodal blue light emission at 405 nm, and grinding or hydrostatic pressure induces double-peak emissions at 405 and 650 nm. Interestingly, double-emission samples can be restored to single-emission samples by short annealing or storage in air for 2 weeks, and this process is reversible. Luminescence response to mechanical stimuli can also be achieved in the presence of hydrochloric acid and water. Spectral analysis and the analysis of the microstructural changes revealed that the structural modifications of the inorganic group play a pivotal role in the response to the stimulus. Finally, a composite film device based on C9H15N3SbCl5 is prepared to demonstrate the potential of these smart materials in anti-counterfeiting and sensing applications. [ABSTRACT FROM AUTHOR]

Memristive devices such as resistive switching memories and artificial synapses have emerged as promising technologies to overcome the technological challenges associated with the von Neumann bottleneck. Recently, lead halide perovskites have drawn substantial research attention as the candidate material for memristors and artificial synapses due to their unique optoelectronic properties, solution processability, and mechanical flexibility. However, the toxicity of lead‐containing species has raised major concerns for health and the environment, which makes it crucial to transition from lead‐based to lead‐free materials for practical applications. Herein, the recent progress of lead‐free metal halides including perovskites and perovskite analogs for resistive memory and artificial synapse is reviewed. Initially, the fundamentals of lead‐free materials and switching mechanisms are introduced. Next, the material design, fabrication technique, and device performance are summarized and critically evaluated for each metal halide species. Finally, the challenges of the lead‐free metal halides toward memristors and artificial synapses are outlined and discussed, and some potential research directions for future study are proposed. [ABSTRACT FROM AUTHOR]

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (glum) is difficult due to usually unmatched electric transition dipole moment (μ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a "cascade cationic insertion" trick to achieve strong CPL (with PLQY of ~100 %) in lead‐free metal halides with high glum values reaching −2.3×10−2 without using any chiral inducers. Achiral solvents of hydrochloric acid (HCl) and N, N‐dimethylformamide (DMF) infiltrate the crystal lattice via asymmetric hydrogen bonding, distorting the perovskite structure to induce the "intrinsic" chirality. Surprisingly, additional insertion of Cs+ cation to substitute partial (CH3)2NH2+ transforms the chiral space group to achiral but the crystal maintains chiroptical activity. Further doping of Sb3+ stimulates strong photoluminescence as a result of self‐trapped excitons (STEs) formation without disturbing the crystal framework. The chiral perovskites of indium‐antimony chlorides embedded on LEDs chips demonstrate promising potential as CPL emitters. Our work presents rare cases of chiroptical activity of highly luminescent perovskites from only achiral building blocks via spontaneous resolution as a result of symmetry breaking. [ABSTRACT FROM AUTHOR]

Regulating the crystal structure of metal halides is important to tune their photoluminescence (PL) or govern the potential emergence of diverse physical properties. Here, an exceptional PL phenomenon characterized by dual‐emission bands in the Mn‐based metal halides (C5H6N)2MnBr4 is observed through hydrostatic pressure measurements. The results have confirmed that the dual‐emission bands centered at ≈518 and 650 nm arise from isolated Mn2+ ions and super‐exchange within Mn2+–Mn2+ dimers, respectively. (C5H6N)2MnBr4 displays remarkable piezochromic luminescence, accompanied by a red shift in dual‐emission. This phenomenon can be attributed to the enhancement of crystal‐field splitting energy and the reduction of relaxation from the low‐energy excited state 4T1 to the ground state 6A1. Meanwhile, the dual‐emission exhibits an anomalous increase ≈1.5–3.9 GPa, which is associated with reduced nonradiative losses during energy migration due to the decreased distance between the luminescent centers as a consequence of lattice contraction. Moreover, (C5H6N)2MnBr4 undergoes a phase transition at ≈1.5 GPa, and upon decompression, the high‐pressure phase partially recovers. This study not only provides insights into the luminescent properties of Mn‐based metal halides but also presents a novel approach to the design of multifunctional photoluminescent materials. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid Ge(II)‐based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics. However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application. In addressing these issues, a breakthrough in the large‐scale production of Sb3+‐doped Ge(IV)‐based metal halide (C13H14N3)2GeCl6 phosphors at room temperature through a straightforward solution method is presented. The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 ± 0.06% the highest among Ge(IV)‐based metal halides. Notably, the introduction of Sb3+ induces the formation of Jahn–Teller‐like self‐trapped excitons in [SbCl6]3− species, attributable to lattice distortion and strong electron–phonon coupling. Consequently, Sb3+‐doped (C13H14N3)2GeCl6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs). Furthermore, the Sb3+‐doped compound exhibits commendable chemical‐ and photostability, prompting exploration in applications such as white light‐emitting diodes and latent fingerprint detection. This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application.

Most of current metal halide materials, including all inorganic and organic–inorganic hybrids, are crystalline materials with poor workability and plasticity that limit their application scope. Here, we develop a novel class of materials termed polymeric metal halides (PMHs) through introducing polycations into antimony‐based metal halide materials as A‐site cations. A series of PMHs with orange‐yellow broadband emission and large Stokes shift originating from inorganic self‐trapped excitons are successfully prepared, which meanwhile exhibit the excellent processability and formability of polymers. The versatility of these PMHs is manifested as the broad choices of polycations, the ready extension to manganese‐ and copper‐based halides, and the tolerance to molar ratios between polycations and metal halides in the formation of PMHs. The merger of polymer chemistry and inorganic chemistry thus provides a novel generic platform for the development of metal halide functional materials. [ABSTRACT FROM AUTHOR]

Ternary indium (In)‐based metal halides are gaining increased attention as promising lead (Pb)‐free alternatives for light‐emitting diodes (LEDs) owing to their broadband emission and high photoluminescence quantum yields (PLQYs). However, most of the pure In‐based compositions suffer from instability against moisture and thermal stress, leading to a rapid degradation of material and hence their optical properties. Herein, a new kind of organic–inorganic hybrid In‐based metal halide BA6InCl9 (BA+ = C4H11N+) is presented, which exhibits stable crystal structure and material composition at both ambient (over 5 months) and heating conditions (up to 200 °C). Besides, the Huang‐Rhys factor of ≈4.94 determined for BA6InCl9 is considerably smaller than most Pb‐free perovskites, which suggests a relatively weak exciton‐phonon coupling in these crystals. By trace amounts of antimony (III) (Sb3+) doping, the PLQY of the BA6InCl9 single crystals can be markedly improved from ≈25% to 95%, and the ensuing down‐conversion LEDs exhibit bright orange‐red emission with an external quantum efficiency of 0.12%, which retains ≈50% of the initial luminance after 380 min of continuous operation in ambient air. It is forseen that the study will prompt future research on In‐based metal halides and their use in stable light‐emitting applications. [ABSTRACT FROM AUTHOR]

Recently, 0D metal halides have attracted widespread interest because of their diverse structures and rich luminescence properties. Nevertheless, the controllable synthesis of metal halide clusters with the ideal configuration using chemical methods remains a great challenge. In addition, the relationship between the coordination configuration and the optical properties of 0D metal halides is not well understood. In this study, two homologous Sb3+‐doped 0D Sn (IV)‐based metal halides with different coordination configurations are developed by inserting a single organic ligand, tetrabutylphosphonium chloride (TBPCl), into a SnCl4 lattice, resulting in different optical properties. Under photoexcitation, Sb3+‐doped (TBP)SnCl5·DMF shows a negligible luminescence from the organic cation of TBP+, while Sb3+‐doped (TBP)2SnCl6 shows a bright orange emission band at 650 nm with a photoluminescence quantum yield (PLQY) of 99%. The above two compounds show quite different optical properties, which should be due to the too‐large lattice distortion of Sb3+‐doped (TBP)SnCl5·DMF, and the DMF will cause the efficient non‐radiation relaxation. In particular, Sb3+‐doped (TBP)2SnCl6 exhibits remarkable anti‐water stability, which shows stability in water for 48 h without structural degradation, and the luminous intensity remains at a high level. Combined with its excellent optical properties and impressive stability, Sb3+‐doped (TBP)2SnCl6 is used in white‐light‐emitting diodes (WLED). [ABSTRACT FROM AUTHOR]

Hybrid metal halides (HMHs) have emerged as a promising platform for optically functional crystalline materials, but it is extremely challenging to thoroughly elucidate the electron transition coupled to additional ligand emission. Herein, to discover sequences of lead‐free HMHs with distinct optically active metal cations are aimed, that is, Sb3+ (5s2) with the lone‐pair electron configuration and In3+ (4d10) with the fully‐filled electron configuration. (Me2NH2)4MCl6·Cl (Me = −CH3, M = Sb, In) exhibits the superior temperature/component‐dependent luminescence behaviors resulting from the competition transition between triplet‐states (Tn‐S0) self‐trapped excitons (STEs) of inorganic units and singlet‐state (S1‐S0) of organic cations, which is manipulated by the optical activity levels of [SbCl6]3− and [InCl6]3−. The bonding differences between Sb3+/In3+ and Cl− in terms of electronic excitation and hybridization are emphasized, and the different electron‐transition mechanisms are established according to the PL spectra at the extreme temperature of 5 to 305 K and theoretical calculations. By fine‐tuning the B‐site Sb3+/In3+ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb3+. This research sheds light on the rules governing PL behaviors of HMHs, as well as exploring the optical‐functional application of aviation temperature sensors and access‐control systems. [ABSTRACT FROM AUTHOR]

Abstract Recently, many lead‐free metal halides with diverse structures and highly efficient emission have been reported. However, their poor stability and single‐mode emission color severely limit their applications. Herein, three homologous Sb3+‐doped zero‐dimensional (0D) air‐stable Sn(IV)‐based metal halides with different crystal structures were developed by inserting a single organic ligand into SnCl4 lattice, which brings different optical properties. Under photoexcitation, (C25H22P)SnCl5@Sb·CH4O (Sb3+−1) does not emit light, (C25H22P)2SnCl6@Sb‐α (Sb3+−2α) shines bright yellow emission with a photoluminescence quantum yield (PLQY) of 92%, and (C25H22P)2SnCl6@Sb‐β (Sb3+−2β) exhibits intense red emission with a PLQY of 78%. The above three compounds show quite different optical properties should be due to their different crystal structures and the lattice distortions. Particularly, Sb3+−1 can be successfully converted into Sb3+−2α under the treatment of C25H22PCl solution, accompanied by a transition from nonemission to efficient yellow emission, serving as a “turn‐on” photoluminescence (PL) switching. Parallelly, a reversible structure conversion between Sb3+−2α and Sb3+−2β was witnessed after dichloromethane or volatilization treatment, accompanied by yellow and red emission switching. Thereby, a triple‐mode tunable PL switching of off–onI–onII can be constructed in Sb3+‐doped Sn(IV)‐based compounds. Finally, we demonstrated the as‐synthesized compounds in fluorescent anticounterfeiting, information encryption, and optical logic gates.

Chiral hybrid organic–inorganic metal halides combining chirality from organic components and optoelectronic properties from the inorganic moieties have attracted considerable interest from the academic community. The field is still in its early stages, especially for low-dimensional (0D, 1D) chiral hybrid organic–inorganic metal halides. Here, we report chiral zero-dimensional metal halides based on chiral nipecotic acid (NA) and tetrabromocuprate. Chiral hybrid organic–inorganic metal halides, [S-NA]2[CuBr4] and [R-NA]2[CuBr4], were synthesized from chiral NA and copper salt via the slow solution evaporation method at room temperature. The obtained crystals were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy spectroscopy, Raman spectroscopy, UV-vis spectroscopy, circular dichroism (CD), thermogravimetry (TG) analysis, and differential scanning calorimetry (DSC). The single crystals were in the orthorhombic system of the chiral non-centrosymmetric space group C2221. These chiral metal halides exhibit typical zero-dimensional (0D) structures. One unit cell contains two chiral NA cations and one tetrabromocuprate ([CuBr4]2−) anion. The organic cations and inorganic anions are alternately arranged and integrated by N–H–Br hydrogen bonds. [S-NA]2[CuBr4] and [R-NA]2[CuBr4] exhibited strong CD signals with opposite values, indicating that these two hybrid organic–inorganic metal halides are enantiomers. The crystal metal halides demonstrate high thermal stability. This work provides a new strategy for designing chiral hybrid organic–inorganic metal halides in low dimensions from various biologically chiral amino acids. [ABSTRACT FROM AUTHOR]

Zero‐dimensional (0D) lead‐free metal halides with efficient photoluminescence (PL) have wide application prospects in the optoelectronics field due to their unique structures and physicochemical properties. However, thermal quenching seriously hinders the practical applications of metal halide materials. Herein, this challenging effort is spearheaded to design novel lead‐free 0D indium‐based chloride K3InCl6:Sb3+ single crystals with zero‐thermal quenching and a near‐unity PL quantum yield based on an effective strategy to suppress non‐radiative transitions. Experimental and computational studies indicate that the intense PL emission originates from self‐trapping excitons (STEs). The extremely low temperature of 7 K and time‐resolved spectra reveal the existence of two individual STEs emissions induced by the distinguished octahedrons in K3InCl6:Sb3+ crystals. Meanwhile, the K3InCl6:Sb3+ crystals can maintain PL stability without thermal quenching over a wide temperature range. Furthermore, the phosphor‐converted light‐emitting diodes can stably operate in the long term, benefitting from the significant structural and PL stability of Sb3+‐doped 0D indium‐based chlorides. Therefore, this work not only presents new 0D metal halides with high efficiency and remarkable stability, but also provides insights into designing high‐performance optoelectronic materials. [ABSTRACT FROM AUTHOR]

Herein, the first report on gel-to-gel transformations via [2 + 2] photopolymerization in MOGs of metal halides and rigid dienes is presented. The MOGs and their xerogels show exceptional ability to undergo [2 + 2] polymerisation upon UV irradiation. Gel-to-gel transformations are very rare as the post-modification of gelators weakens the gel and transforms it to a sol. Such transformations change the molecular assemblies into gels with altered mechanical and chemical properties. These phenomena pave the way to synthesize new MOGs with improved rigidity that cannot be synthesized otherwise. [ABSTRACT FROM AUTHOR]

Ion migration‐induced noise is the main limiting factor for metal halides (MHs) single crystals (SCs) X‐ray detectors, and heterostructure design is the most efficient method to overcome this puzzle. However, the conventional stepwise solution method or heteroepitaxial method is greatly limited by the SCs secondary dissolution and the lattice parameters matching. Here, simple and universal crystalline–amorphous heterojunction is developed that proves to be extremely effective in suppressing noise. MAPbBr3 SCs are first chosen as representatives to form heterojunctions with amorphous MTP2MnBr4 by the melting method, and the related device shows an enhanced X‐ray response with significant noise suppression. Computational and experimental results demonstrate that the gradient energy levels formation and improved ion migration energy are responsible for this. Finally, the optimized device shows a low dark current (reduced from ≈1000 to ≈0.12 nA), ultra‐high sensitivity (10 569 µC Gyair−1 cm−2), lower detection limit (82.64 nGyair s−1), and negligible performance deterioration at a total radiation dose of ≈17 000 mGyair. Moreover, six other SCs are selected to verify the universal effect of the heterojunctions, all of which show excellent improved sensitivity, proving its versatility. Hence, it is believed that this work will give a strong impetus to develop sensitive MHs SCs X‐ray detectors. [ABSTRACT FROM AUTHOR]

Lead‐free metal halides are considered a new generation of optoelectronic materials due to their low toxicity, superior optoelectronic properties, ease of synthesis, structural diversity, and low cost. In particular, Mn2+‐based metal halides have earned intensive attention owing to their high emission quantum efficiency, rich physical properties (e.g., triboluminescence and stimuli‐responsivity), low cost, and toxicity. Due to the different coordination environments of Mn ions, Mn2+‐based metal halides can exhibit green, red, and near‐infrared emissions. This review summarizes the recent progress of Mn2+‐based metal halides in synthesis methods, emission mechanisms, photophysical properties, and representative applications in X‐ray scintillations, white light‐emitting diodes, optical anti‐counterfeiting technologies, and fluorescent sensors. Finally, the challenges and potential research directions toward developing Mn2+‐based metal halides are also predicted. [ABSTRACT FROM AUTHOR]

Flat-panel x-ray scintillators with a high spatial resolution at a low radiation dose rate are desirable for efficient imaging applications in medical diagnostics, security inspection, and nondestructive inspection. To promote the progress of x-ray imaging technologies, it is of great interest to explore transparent scintillators with reduced light scattering, high light yields, and uniform radioluminescence. Herein, we design and prepare a novel lead-free (C12H28N)2Cu2I4 metal halide featuring a high luminescent efficiency and white emission benefiting from the double self-trapped exciton mechanism, which enable to not only match the response of semiconductor-based sensors but also enhance light yields and decrease exposed doses to objects. Furthermore, transparent, and flexible scintillators with large areas of 20.25 cm2 demonstrate an outstanding scintillation performance including a high spatial resolution of 19.8 lp mm−1 and an ultralow detection limit of 28.39 nGyair s−1, which are ∼4 times higher and 194 times lower than typical values for medical imaging, respectively. This work provides not only a new route to explore promising alternatives with broadband emission but also a novel opportunity to develop flexible x-ray imaging technology. [ABSTRACT FROM AUTHOR]

Chiral hybrid metal halides have been widely studied in the field of photondetectors, chiral optics, and spintronics due to their great structural flexibility and suitable bandgaps. Inspired by such great progress made in the abovementioned fields, continuous efforts need to be paid to seek other interesting applications for chiral hybrid metal halides. Herein, the synthesis of a pair of one‐dimensional enantiomorphic hybrid metal halide piezoelectrics, R/SMPCdCl4(R/SMP = R/S‐2‐methylpiperazine), and their applications in piezoelectric energy harvesting and sensing are reported. Density functional theory calculations show that these chiral piezoeletrics possess low elastic properties and high piezoelectric constants (16.71, 8.39, and 7.35 pC N−1). In addition, devices made of RMPCdCl4/PDMS (PDMS = polydimethylsiloxane) composite films are fabricated for piezoelectric energy harvesting and sensing. The piezoelectric energy harvesters with optimized content of 15 wt% RMPCdCl4/PDMS show not only excellent performance with an open‐circuit voltage of 2.57 V, short‐circuit current of 0.37 μA, and power density of 0.55 μW cm−2 but also outstanding stability of more than 3500 cycles. Meanwhile, these piezoelectric energy harvesters exhibit prominent sensing properties for detecting tapping, finger bending, walking, and running. It is demonstrated that chiral hybrid metal halides hold great potential in intelligent wearable and sensing devices.

The Sb3+ doping strategy has been proven to be an effective way to regulate the band gap and improve the photophysical properties of organic-inorganic hybrid metal halides (OIHMHs). However, the emission of Sb3+ ions in OIHMHs is primarily confined to the low energy region, resulting in yellow or red emissions. To date, there are few reports about green emission of Sb3+-doped OIHMHs. Here, we present a novel approach for regulating the luminescence of Sb3+ ions in 0D C10H22N6InCl7·H2O via hydrogen bond network, in which water molecules act as agents for hydrogen bonding. Sb3+-doped C10H22N6InCl7·H2O shows a broadband green emission peaking at 540 nm and a high photoluminescence quantum yield (PLQY) of 80%. It is found that the intense green emission stems from the radiative recombination of the self-trapped excitons (STEs). Upon removal of water molecules with heat, C10H22N6In1-xSbxCl7 generates yellow emission, attributed to the breaking of the hydrogen bond network and large structural distortions of excited state. Once water molecules are adsorbed by C10H22N6In1-xSbxCl7, it can subsequently emit green light. This water-induced reversible emission switching is successfully used for optical security and information encryption. Our findings expand the understanding of how the local coordination structure influences the photophysical mechanism in Sb3+-doped metal halides and provide a novel method to control the STEs emission.

Organic–inorganic metal halides (OIMHs) with high‐efficiency solar spectrum‐like emission are attracting broad and current interest. Here, five 0D Zn‐based hybrid halides are synthesized based on aromatic organic cations with different carbon‐chain lengths: C6H5CH2NH3+ (PMA+) and C6H5(CH2)4NH3+ (PBA+). (PMA)2ZnCl4 exhibits the highest photoluminescence quantum yield of 37.2% of reported Zn‐based white‐emission OIMHs. The emission spectrum of (PBA)2ZnI4 indicates a color rendering index of 98, which is the highest among single‐component white‐light‐emitting phosphors. Spectral characterizations and density functional theory calculations demonstrate that the extremely broad emission of (PBA)2ZnI4 originates from the synergistic emission of organic cations and self‐trapped excitons. The optical properties of the obtained (PMA)2ZnBr4, (PMA)2ZnI4·H2O, and (PBA)2ZnCl4 are also characterized for comparison, and with the same organic cations, the PLQY decreases from chloride to bromide to iodide. This work demonstrates that the selection of appropriate organics and halogens can enable fine tuning of single‐component white‐light emission, satisfying varying needs for solid‐state lighting. [ABSTRACT FROM AUTHOR]

Dimension growth of metal halides is important for its properties and applications. However, such dimension control of the metal halides is rarely reported in the literature and the growth mechanism is not clear yet. A minute difference of solvent properties can tremendously alter the process of nucleation and growth of crystals. Herein, an intriguing phenomenon of dimension tuning for Ag‐based metal halides is reported. The 1D Cs2AgCl3 crystals can be obtained in pure DMF while the 2D CsAgCl2 crystals are obtained in pure DMSO. Both exhibit bright yellow emission, which are derived from self‐trapping excitons (STEs). The photoluminescence quantum yield (PLQY) of Cs2AgCl3 (1D) and CsAgCl2 (2D) are 28.46 % and 20.61 %, respectively. In order to understand the mechanism of the dimension change, additional solvents (N,N‐dimethylacetamide, DMAC, 1,3‐Dimethyl‐Tetrahydropyrimidin‐2(1H)‐one, DMPU) are also selected to process the precursor for crystal growth. By comparing the functional group, dielectric constant, and donor number among the four solvents, we find the donor number plays the predominant role in nucleation process for Cs2AgCl3 and CsAgCl2. This research reveals the relationship between coordination ability of the solvent and the dimension of metal halides. [ABSTRACT FROM AUTHOR]

Low dimensional lead‐free metal halides have become the spotlight of the research on developing multifunctional optoelectronic materials as their properties show a wide range of tunability. However, most reported low dimensional metal halides only function in the ultra‐violet to visible range due to their large bandgap. Moreover, the organic cation based low dimensional metal halides show limited thermal stability; on the other hand, their inorganic cation based counterparts suffer from limited solution processability. A hybrid cation approach is proposed, where a zero dimensional (0D) metal halide ((DFPD)2CsBiI6) is developed by using mixed organic–inorganic cations: 4, 4‐difluoropiperidine (DFPD) and cesium (Cs+). This ensures both thermal stability and solution processability. Furthermore, [BiI6]3− octahedra are serving as active light absorption units, which ensures the bandgap to be located at the visible region. Its photoluminescence (PL) is further shifted to the near infrared (NIR) region by doping (DFPD)2CsBiI6 with antimony (Sb3+). The developed materials show multifunctional properties: thermochromic behavior, light detection, and NIR light emitting. This study expands the scope of developing multifunctional 0D metal halides. [ABSTRACT FROM AUTHOR]