Metal Halide Materials Research Articles

Sn(II)-doped one-dimensional hybrid metal halide [C5H14NO]CdCl3 single crystals with broadband greenish-yellow light emission.

Low-dimensional organic-inorganic hybrid halides, as an important branch of metal halide materials, have attracted much attention due to their excellent photoelectric properties. Herein, we designed one new hybrid cadmium chloride [C5H14NO]CdCl3 based on combinations of the d10 metal cation (Cd2+) and choline chloride molecules. [C5H14NO]CdCl3 single crystals belong to the orthorhombic Pna21 space group and show a one-dimensional (1D) structure with distorted [CdCl5O]5- octahedra. The second harmonic generation (SHG) response of [C5H14NO]CdCl3 exhibits an intensity of approximately 0.4 × KDP. Moreover, the photoluminescence properties of the [C5H14NO]CdCl3 crystal are activated by doping with Sn2+ ions having stereochemically active lone pair 5s2 electrons. Under UV excitation conditions, bright greenish-yellow light emission can be observed, and the quantum efficiency (PLQY) is as high as 91.27%. The luminescence mechanism is revealed by combining the results of temperature dependent luminescence and density functional theory (DFT) calculation. This work can serve as a guide for the design and synthesis of emerging optical materials.

Admirable stability achieved by ns2 ions Co-doping for all-inorganic metal halides towards optical anti-counterfeiting.

Optical materials play a momentous role in anti-counterfeiting field, such as authentication, currency and security. The development of tunable optical properties and optical responses to a range of external stimuli is quite imperative for the growing demand of optical anti-counterfeiting technology. Metal halide perovskites have attracted much attention of researchers due to their excellent optical properties. In addition, co-doping methods have been gradually applied to the research of metal halide perovskites, by which more abundant luminescence phenomena can be introduced into the host perovskite. Herein, the ns2 ions of bismuth (Bi3+) and antimony (Sb3+) ions co-doped zero-dimensional Cs2SnCl6 metal halide with an excitation-wavelength-dependent emission phenomenon is synthesized as an efficient multimodal luminescent material, the luminescence of which is tunable and covers a wide region of color. What's more, a dynamic dual-emission phenomenon is captured when the excitation wavelength changes from 320 nm to 420 nm for Cs2SnCl6:Bi0.08Sb0.12 crystals. Moreover, the Bi3+ and Sb3+ doped metal halide material shows great enhancement in solvent resistance and thermal stability compared to the pristine Cs2SnCl6. The admirable stability and distinguishable photoluminescence (PL) phenomenon of this all-inorganic metal halide has great potential to be applied in optical anti-counterfeiting technology. Furthermore, the co-doping method can accelerate the discovery of new luminescence phenomena in original metal halide perovskites.

Recent Progress of Bismuth Effect on All‐Inorganic Lead‐Free Metal Halide Derivatives: Crystals Structure, Luminescence Properties, and Applications

AbstractBismuth (Bi3+)‐included lead‐free metal halide (LFMH) materials attract much attention in lighting, display, photodetectors, X‐ray detectors, and photovoltaic fields, due to the tunable luminescence and optoelectronic performance in response to crystal and electronic structure, morphology, and particle sizes. This review summarizes Bi3+‐included LFMH materials about their preparation approach, crystal and electronic structure properties, luminescence performance, and emerging applications. Notably, Bi3+ ions not only can act as framework cation to construct stable LFMH structure, but can also incorporate into LFMH materials as activators or sensitizers to generate remarkable luminescence tuning and band engineering. The Bi3+ effect on the luminescence and optoelectronic properties of LFMH materials, including, promotion of exciton localization, enhancement of light absorption in near‐ultraviolet region, action as sensitizer ions to transfer energy to rare earth or transition metal ions and emission of highly‐efficient light is systematically summarized. The proposed structure‐luminescence relationship offers guidance for the optimization of current Bi3+‐included LFMH materials and the exploitation of new LFMH derivatives.

Zero-dimensional rubidium zinc halide blue-emitting quantum dots for X-ray imaging

Low-dimensional-networked metal halide (MH) materials are emerged as a new class of semiconductors owing to their unique structure and outstanding photoelectric properties. Compared with the extensively studied three-dimensional (3D) MHs, the zero-dimensional (0D) MHs are of great interest to be widely studied. Here we report the successful colloidal synthesis of all-inorganic lead-free 0D MHs, including undoped and Cu-doped Rb2ZnCl4 quantum dots (QDs) with bright broad blue and cyan emissions, respectively. Combining the theoretical and experimental study, the band structures are well characterized and the originations of the blue and cyan emissions are attributed to the singlet and triplet self-trapped exciton (STE) emissions, respectively. Finally, owing to the bright radioluminescence (RL), the Cu-doped Rb2ZnCl4 QDs is prepared into a thin film to demonstrate the feasibility for X-ray imaging application. This work not only provides a cyan-emitting all-inorganic 0D MH QDs, but also exploits it as a scintillator for X-ray imaging.

Hybrid Germanium Bromide Perovskites with Tunable Second Harmonic Generation

AbstractGe‐based hybrid perovskite materials have demonstrated great potential for second harmonic generation (SHG) due to the geometry and lone‐pair induced non‐centrosymmetric structures. Here, we report a new family of hybrid 3D Ge‐based bromide perovskitesAGeBr3,A=CH3NH3(MA), CH(NH2)2(FA), Cs and FAGe0.5Sn0.5Br3, crystallizing in polar space groups. These compounds exhibit tunable SHG responses, where MAGeBr3shows the strongest SHG intensity (5×potassium dihydrogen phosphate, KDP). Structural and theoretical analysis indicate the high SHG efficiency is attributed to the displacement of Ge2+along [111] direction and the relatively strong interactions between lone pair electrons of Ge2+and polar MA cations along thec‐axis. This work provides new structural insights for designing and fine‐tuning the SHG properties in hybrid metal halide materials.

Green Triplet Self-Trapped Exciton Emission in Layered Rb3Cd2Cl7:Sb3+ Perovskite: Comparison with RbCdCl3:Sb3.

Metal halide materials have recently sparked intense research because of their excellent photophysical properties and chemical stability. For example, RbCdCl3:Sb3+ exhibits broad emission at about 600 nm with a high photoluminescence quantum yield (PLQY) over 91% and double emission bands with bright white color. Herein, we obtained a novel Rb and Cd layered perovskite Rb3Cd2Cl7 doped with Sb3+, which gives luminescence at 525 nm with a large Stokes shift of 200 nm, originating from a self-trapped exciton (STE). Its PLQY is 57.47%, but its low-temperature PLQY becomes much higher at the same wavelength. When Rb3Cd2Cl7:Sb3+ and RbCdCl3:Sb3+ were compared, the two classes of quantum confinement effects by Rb and Cd ions in the lattice were identified to describe their electronic states and different optical properties. These results suggest that properties of Sb-doped cadmium halides could be modified by the structure type and local atomic confinement to find applications as promising luminescent materials for optoelectronic devices.

Mn and Cu codoped Cs2ZnBr4 metal halide with multiexcitonic emission toward anti-counterfeiting

The growing demand for optical anti-counterfeiting technology requires the development of new environmentally-friendly smart materials with single-component, multimodal fluorescence. Herein, Cs2ZnBr4:0.3Mn2+&0.15Cu+, as an efficient multimodal luminescent material with excitation-wavelength-dependent emission is reported. Under 365 nm and 254 nm UV light excitation, Cs2ZnBr4:Mn2+&Cu+ emits mutually independent green light at 525 nm and blue light at 470 nm, which origin from the emission of Mn2+ and the Cu+ enhanced self-trapped excitons of Cs2ZnBr4, respectively. Furthermore, the multiexcitonic emission is applied to anti-counterfeiting applications and information encryption and decryption engineering. This codoped strategy provides a colorful step to expand the new metal halide materials in fluorescent anti-counterfeiting and information encryption and decryption.

Efficient and Stable Self‐Trapped Blue Emission from a 1D Organolead Chloride Crystalline Material

AbstractIntrinsic blue emission with high stability and high efficiency remains to be a great challenge for metal halide hybrids. In this study, a single‐crystalline, ultrastable self‐trapped blue‐light emitter based on 1D cationic [Pb2Cl2]2+ haloplumbate chains is discovered, which affords a Stokes shift of 78 nm and Commission Internationale de l'Eclairage chromaticity coordinates of (0.156, 0.080), very close to blue standard (0.140, 0.080). The Stokes shift is the lowest reported value among the intrinsic self‐trapped emission from the vast majority of organometal halide hybrids. Moreover, the presence of out‐of‐plane chloride results in highly localized self‐trapped excitons in 1D cationic chains and high photoluminescence quantum yield of 72%, which exceeds many intrinsic blue‐light‐emitting metal halide materials. Analogous to the previously reported organocarboxylate‐based lead halide hybrids, the material exhibits ultrastable continuous photoemission in air for at least 24 h and maintains the efficient emission after a variety of thermal or chemical treatments. The excellent blue‐light‐emitting performance of the material enables its promising applications in high‐definition lighting and display fields.

0D chiral hybrid indium(III) halides for second harmonic generation.

Chiral metal halides have shown great potential for application in next generation nonlinear optical (NLO) devices owing to their intrinsic non-centrosymmetry. However, the structures and properties of chiral hybrid indium halides have been rarely reported, especially when it comes to second-harmonic generation (SHG) in NLO. In this work, we have synthesized a pair of new zero-dimensional (0D) chiral hybrid indium halides, (R-MPEA)6InCl9 and (S-MPEA)6InCl9, and studied their NLO properties. The as-prepared chiral hybrid indium halides crystallize in non-centrosymmetric P3221 and P3121 space groups, respectively. NLO studies show that 0D chiral hybrid indium halide crystals exhibit strong SHG responses with high polarization ratio and high laser damage threshold (LDT). This work enriches the family of chiral hybrid metal halide materials and offers a feasible strategy for the targeted design and synthesis of intrinsically non-centrosymmetric metal halide materials for NLO applications.

A Zero-Dimensional Hybrid Cadmium Perovskite with Highly Efficient Orange-Red Light Emission.

Low-dimensional organic-inorganic hybrid metal halide materials have been extensively studied due to their excellent optoelectronic performances. Herein, by using the facile wet-chemistry method, we designed one new hybrid cadmium bromide of (H3AEP)2CdBr6·2Br based on discrete octahedral [CdBr6]4- units. Remarkably, the bulk crystal of (H3AEP)2CdBr6·2Br exhibits strong broadband orange-red light emission from the radiative recombination of self-trapped excitons (STEs) with a high photoluminescence quantum yield (PLQY) of 9%. Benefiting from the highly efficient luminescent performance, this 0D cadmium perovskite can be utilized as an excellent down-conversion red phosphor to assemble a white light-emitting diode, and a high color rendering index (CRI) of 93 is realized. As far as we know, this is the first orange-red light-emitting hybrid cadmium perovskite which promotes the full-color display in this system.

Self-Trapped Exciton Emission in a Zero-Dimensional (TMA)2SbCl5·DMF Single Crystal and Molecular Dynamics Simulation of Structural Stability.

Lead-free lower-dimensional organic-inorganic metal halide materials have recently triggered intense research because of their excellent photophysical properties and chemical stability. Herein, we report a novel zero-dimensional (0D) organic-inorganic hybrid single crystal (TMA)2SbCl5·DMF (TMA = N(CH3)3, DMF= HCON(CH3)2), which exhibits typical self-trapped exciton (STE) emission with an efficient yellow emission at 630 nm and high photoluminescence quantum yield (PLQY) of 67.2%. The dual STE emission is attributed to the singlet and triplet STEs in inorganic [SbCl5]2-, respectively. Further, an ab initio molecular dynamics simulation was performed to estimate the stability of crystal structure at room temperature. The calculated excited-state structure indicates that the deformation parameter (Δd) of the excited-state structure is larger than that of the ground state, illustrating the origin of a large Stokes shift. These results indicate that these new 0D lead-free organic-inorganic hybrid metal halides are promising luminescent materials for optoelectronic applications.

Water-Stable Zero-Dimensional (C4H9)4NCuCl2 Single Crystal with Highly Efficient Broadband Green Emission.

Here, we report (C4H9)4NCuCl2 single crystals with a luminous intensity that remains largely the same after soaking in water for 24 h. (CH9)4NCuCl2 has a new type zero-dimensional framework, in which the isolated [CuCl2]- anions are wrapped by organic (C4H9)4N+ cations. As expected, (C4H9)4NCuCl2 shows a broad emission band at 508 nm with a photoluminescence quantum yield of approximately 82% at room temperature, stemming from self-trapped exciton (STE) emission. Temperature-dependent photoluminescence measurement reveals that there is an energy barrier ΔE (24.0 meV) between the intrinsic state and STE state, which leads to the increase in emission intensity with an increase in temperature (98-278 K), while the emission intensity begins to decrease when the temperature is higher than 278 K due to the effects of both thermal quenching and carrier scattering. Our findings provide a new idea for the design of lead-free anti-water stability metal halide materials.

Sb3+‐Doping in Cesium Zinc Halides Single Crystals Enabling High‐Efficiency Near‐Infrared Emission

AbstractLuminescent metal halide materials with flexible crystallography/electronic structures and tunable emission have demonstrated broad application prospects in the visible light region. However, designing near‐infrared (NIR) light‐emitting metal halides remains a challenge. Here, an enlightening prototype is proposed to explore the high‐efficiency broadband NIR emission in metal halide systems by incorporating Sb3+ into the Cs2ZnCl4 matrix. Combined experimental analysis and density functional theory calculations reveal a modified self‐trapped excitons model to elaborate the NIR emission. The high photoluminescence quantum yield of 69.9% peaking at 745 nm and large full width at half maximum of 175 nm, along with excellent air/thermal stability, show the unique advantages of lead‐free metal halide Cs2ZnCl4:Sb3+ as the NIR light source. The substitution of Cl− by Br− further enables the red‐shift of emission peak from 745 to 823 nm. The NIR light‐emitting diode device based on Cs2ZnCl4:Sb3+ demonstrates potential as a non‐visible light source in night vision. This study puts forward an effective strategy to design the novel eco‐friendly and high‐efficiency NIR emissive materials and provides guidance for expanding the application scope of luminescent metal halides.

Polarons and Charge Localization in Metal-Halide Semiconductors for Photovoltaic and Light-Emitting Devices.

Metal-halide semiconductors have shown excellent performance in optoelectronic applications such as solar cells, light-emitting diodes, and detectors. In this review the role of charge-lattice interactions and polaron formation in a wide range of these promising materials, including perovskites, double perovskites, Ruddlesden-Popper layered perovskites, nanocrystals, vacancy-ordered, and other novel structures, is summarized. The formation of Fröhlich-type "large" polarons in archetypal bulk metal-halide ABX3 perovskites and its dependence on A-cation, B-metal, and X-halide composition, which is now relatively well understood, are discussed. It is found that, for nanostructured and novel metal-halide materials, a larger variation in the strengths of polaronic effects is reported across the literature, potentially deriving from variations in potential barriers and the presence of interfaces at which lattice relaxation may be enhanced. Such findings are further discussed in the context of different experimental approaches used to explore polaronic effects, cautioning that firm conclusions are often hampered by the presence of alternate processes and interactions giving rise to similar experimental signatures. Overall, a complete understanding of polaronic effects will prove essential given their direct influence on optoelectronic properties such as charge-carrier mobilities and emission spectra, which are critical to the performance of energy and optoelectronic applications.

Light-Emitting Metal-Organic Halide 1D and 2D Structures: Near-Unity Quantum Efficiency, Low-Loss Optical Waveguide and Highly Polarized Emission.

Organic-inorganic metal-halide materials (OIMMs) with zero-dimensional (0D) structures offer useful optical properties with a wide range of applications. However, successful examples of 0D structural OIMMs with well-defined optical performance at the micro-/nanometer scale are limited. We prepared one-dimensional (1D) (DTA)2 SbCl5 ⋅DTAC (DTAC=dodecyl trimethyl ammonium chloride) single-crystal microrods and 2D microplates with a 0D structure in which individual (SbCl5 )2- quadrangular units are completely isolated and surrounded by the organic cation DTA+ . The organic molecular unit with a long alkyl chain (C12 ) and three methyl groups enables microrod and -plate formation. The single-crystal microrods/-plates exhibit a broadband orange emission peak at 610 nm with a photoluminescence quantum yield (PLQY) of ca. 90 % and a large Stokes shift of 260 nm under photoexcitation. The broad emission originates from self-trapping excitons. Spatially resolved PL spectra confirm that these microrods exhibit an optical waveguide effect with a low loss coefficient (0.0019 dB μm-1 ) during propagation, and linear polarized photoemission with a polarization contrast (0.57).

Photoluminescence of Singlet/Triplet Self‐Trapped Excitons in Sb3+‐Based Metal Halides

AbstractEmerging lead‐free metal halides with low toxicity and unparalleled optoelectronic properties have attracted growing research interests, also demonstrating extensive application potentials. Among these, Sb3+‐based all‐inorganic/organic–inorganic hybrid metal halides become a vital group due to the special energy level distribution along with diverse optical properties. However, there remains a gap in understanding the relationship between the crystal structure and the radiation process of involved Sb3+ emission. Herein, the existing reports about Sb3+‐based luminescent metal halides are revisited and their structure–luminescence–application relationship is explored, and it is further established that the triplet self‐trapped excitons (STEs) emission of Sb3+ varies in different crystallographic environments and endows tunable luminescent performance. This work aims to provide constructive strategies in the further exploitation of Sb3+‐based metal halides, and also guides the structural design and photoluminescence tuning of doped metal halide materials.

Mixed Group 14–15 Metalates as Model Compounds for Doped Lead Halide Perovskites

Doping and alloying are valuable tools for modifying and enhancing the properties and performance of lead halide perovskites. However, the effects of heterovalent doping with Sb3+ and Bi3+ cations are still a matter of current investigation. Due to the different charge of the dopants compared to the constituting Pb2+ ions, a simultaneous creation of defects is unavoidable and the influence of these defects and the actual metal substitution become entangled. Herein, we present the first 14–15 iodido metalates, (BED)4PbE2I16 (BED=N‐benzylethylenediammonium; E=Sb (1), Bi (2)), which are model compounds for doped lead iodide perovskites and display surprisingly low band gaps of 2.01 (1) and 1.88 eV (2). Quantum chemical investigations show that this stems from a good electronic match between the PbI6 and EI6 units of the compounds. Our results provide a model system for doped perovskites, but also represent the first examples of a promising new class of metal halide materials.

Modulation of Metal Halide Structural Units for Light Emission.

ConspectusWith the development of solid-state lighting technology, efficient light sources that combine high brightness, wide range, and good stability are in high demand for next-generation lighting and displays. Metal halides are emerging as promising luminescent materials due to their versatility for desirable light emission manipulations. This is because the optical activity of the metal halide material depends on the metal halide structural unit and the organic ions or coordinated organic ligands. The different assembly of metal halide units and organic parts can enable versatile light emissions, such as lead halide perovskites (LHPs) and copper halide-organic hybrids. Impressively, the external quantum efficiency of the LHP based light-emitting diodes (LEDs) has improved significantly from 0.1% to over 20% in just five years. With this great progress, the structural lability and toxicity of the LHPs are now the critical issues that need to be addressed for practical applications. These issues are mainly rooted in the intrinsic lead composition and low formation energy crystal structure of the widely adopted LHPs. Thus, the modulation of the structure and composition of the basic metal halide structural units is considered a rational strategy to address these issues.In this Account, we will present a general material design using metal halide structural units as basic building blocks to build up metal halide luminescent materials for solid-state lighting devices. Following this route, we will emphasize the modulation of metal halide structural units to tackle the existing challenges in lead halides, including the instability of crystalline structure, ion migration, and the presence of toxic lead. Considering basic components in structural units, we will highlight ionic engineering in LHPs via ion doping, substitution, and modification to enhance the crystal structural stability and suppress ion migration. To replace toxic lead, we will introduce recent advances in the modulation of lead-free halide structural units by active ion doping and organic ligand coordination to fabricate highly luminescent materials. Finally, we will present future strategies of metal halide structural unit modulation for solid-state light emissions. We hope this Account will provide new insights for designing metal halide materials from the viewpoint of the modulation of the basic building blocks and inspire future studies of advanced metal halide materials for solid-state light emitting applications.

Down and up conversion luminescence of the lead-free organic metal halide material: (C9H8NO)2SnCl6·2H2O

The present work deals with the optical properties of hybrid organic metal halide material namely (C9H8NO)2SnCl6·2H2O. Its structure is built up from isolated [SnCl6]2- octahedral dianions surrounded by Hydroxyl quinolinium organic cations (C9H8NO)+, abbreviated as [HQ]+. Unlike the usual hybrid materials, where metal halide ions are luminescent semiconductors while the organic ones are optically inactive, [HQ]2SnCl6·2H2O contains two optically active entities: [HQ]+ organic cations and [SnCl6]2- dianions. The optical properties of the synthesized crystals were studied by optical absorption spectroscopy, photoluminescence measurements and DFT calculations of electronic density of states. These studies have shown that both organic and inorganic entities have very close HOMO-LUMO gaps and very similar band alignments favoring the resonant energy transfer process. In addition, measurements of luminescence under variable excitations reveal an intense green luminescence around 497 nm under UV excitation (down conversion) and infrared excitation (up conversion luminescence). The down conversion luminescence is assigned to the π-π* transition within the [HQ] + organic cations involving charge transfer between the organic and inorganic entities, whereas the up-conversion luminescence is based on the triplet-triplet annihilation mechanism (TTA).

Tuning the Bandgap in Silver Bismuth Iodide Materials by Partly Substituting Bismuth with Antimony for Improved Solar Cell Performance

Silver bismuth iodide (Ag-Bi-I) light absorbers are interesting candidates as lead-free and low-toxic metal-halide materials for solar cell applications. In this work, the partial exchange of bismu ...