Low-dimensional Metal Halides Research Articles

Antiferromagnetic Ordering in A One-Dimensional Organic Copper Chloride Hybrid Insulator.

Low dimensional (LD) organic metal halide hybrids (OMHHs) have recently emerged as new generation functional materials with exceptional structural and property tunability. Despite the remarkable advances in the development of LD OMHHs, optical properties have been the major functionality extensively investigated for most of LD OMHHs developed to date, while other properties, such as magnetic and electronic properties, remain significantly under-explored. Here we report for the first time the characterization of the magnetic and electronic properties of a 1D OMHH, organic-copper (II) chloride hybrid (C8H22N2)Cu2Cl6. Owing to the antiferromagnetic coupling between Cu atoms through chloride bridges in 1D [Cu2Cl62-]∞ chains, (C8H22N2)Cu2Cl6 is found to exhibit antiferromagnetic ordering with a Néel temperature of 24K. The two-terminal (2T) electrical measurement on a (C8H22N2)Cu2Cl6 single crystal reveals its insulating nature. This work shows the potential of LD OMHHs as a highly tunable quantum material platform for spintronics.

Antiferromagnetic Ordering in A One‐Dimensional Organic Copper Chloride Hybrid Insulator

Low dimensional (LD) organic metal halide hybrids (OMHHs) have recently emerged as new generation functional materials with exceptional structural and property tunability. Despite the remarkable advances in the development of LD OMHHs, optical properties have been the major functionality extensively investigated for most of LD OMHHs developed to date, while other properties, such as magnetic and electronic properties, remain significantly under‐explored. Here we report for the first time the characterization of the magnetic and electronic properties of a 1D OMHH, organic‐copper (II) chloride hybrid (C8H22N2)Cu2Cl6. Owing to the antiferromagnetic coupling between Cu atoms through chloride bridges in 1D [Cu2Cl62‐]∞ chains, (C8H22N2)Cu2Cl6 is found to exhibit antiferromagnetic ordering with a Néel temperature of 24K. The two‐terminal (2T) electrical measurement on a (C8H22N2)Cu2Cl6 single crystal reveals its insulating nature. This work shows the potential of LD OMHHs as a highly tunable quantum material platform for spintronics.

Temperature and pressure-responsive photoluminescence in a 1D hybrid lead halide

Low-dimensional hybrid lead halides with responsive emissions have attracted considerable attention due to their potential applications in sensing. Herein, a new one-dimensional hybrid lead bromide CyPbBr3 (Cy = cytosine cation) was synthesized to explore its emission evolution in response to temperature and pressure. The compound possesses an edge-sharing 1D double-chain structure and emits warm white light across nearly the entire visible spectrum upon ultraviolet excitation. This emission arises from the self-trapped excitons and its broadband feature is attributed to the strong electron-phonon coupling as revealed by the variable-temperature photoluminescence experiments. Moreover, a 4.5-fold pressure-induced emission enhancement was observed at 2.7 GPa which is caused by the pressure suppressed non-radiative energy loss. Furthermore, in-situ powder X-ray diffraction and Raman experiments reveal the maxima of the emission enhancement is associated with a phase transition at the same pressure. Our work demonstrates that low-dimensional metal halides are a promising class of stimuli-responsive materials which could have potential use in temperature and pressure sensing.

Warm white-light emission from self-trapped excitons in double-chain metal halide hybrid

Low-dimensional metal halide hybrids with efficient warm white-light emission from self-trapped excitons (STEs) have attracted extensive attention for interior lighting because of their fascinating emission features including high colour rendition, excellent colour stability, and low manufacturing cost. Despite great efforts, the mechanism of STEs in one-dimensional (1D) metal halide hybrids is still unclear, which makes the way to regulate white-light emission is still worth exploring. Here, we prepared a double-chain organic-inorganic metal halide hybrid crystal, (C6H18N2)Pb2Br6∙H2O (DEPBH). Strikingly, DEPBH shows a warm white-light emission with an appropriate correlated colour temperature of 3714 K and high colour rendering index up to 89. Especially, further research reveals that STEs springs from the 1D core-shell quantum-wire frame play a crucial role in such warm white-light emission of DEPBH. This work offers a new route to fabricate single-component warm white-light phosphors in low-dimensional materials and will contribute to the further exploration of their relationships between crystal structure and optical properties.

Boosting Blue Self-Trapped Exciton Emission in All-Inorganic Zero-Dimensional Metal Halide Cs2ZnCl4 via Zirconium (IV) Doping.

Low-dimensional metal halides with efficient luminescence properties have received widespread attention recently. However, nontoxic and stable low-dimensional metal halides with efficient blue emission are rarely reported. We used a solvothermal synthesis method to synthesize tetravalent zirconium ion-doped all-inorganic zero-dimensional Cs2ZnCl4 for the first time. Bright blue emission in the range of 370 nm-700 nm with a emission maximum at 456 nm was observed in Zr4+:Cs2ZnCl4 accompanied by a large Stokes shift, which was due to self-trapped excitons (STEs) caused by the lattice vibrations of the twisted structure. Simultaneously, the PLQY of Zr4+:Cs2ZnCl4 achieve an impressive 89.67%, positioning it as a compelling contender for future applications in blue-light technology.

Solvent-Induced Bright Emission in Lead-Free Organic-Inorganic Antimony Bromides with Reversible Transformation.

Lead-free low-dimensional organic-inorganic metal halides have gained increasing attention in a wide range of applications due to their low toxicity, outstanding optical performance, and structural tunability. In this work, a general method of incorporating organic molecule into sodium antimony bromides is introduced. The 1D Na3SbBr6(C2H6OS)6 and Na3SbBr6(C4H8OS)6 single crystals exhibit bright yellow and orange emission with PL peaks at 610 and 664nm, and high photoluminescence quantum yields (PLQYs) of 85% and 60%, respectively. These two compounds can be reversibly converted into each other by the removal and addition of the organic components. Their exceptional luminescent performance enables them to be used as solid-state phosphors for the fabrication of yellow and orange down-conversion LEDs. A white LED with a high color rendering index (CRI) of 95 is also fabricated by using Na3SbBr6(C2H6OS)6 as the yellow phosphor. The universality of this method is demonstrated by synthesizing other members of this family with diverse A-groups, including methylammonium (MA) and formamidinium (FA). This work provides an effective strategy for the development of diverse lead-free and high-performance organic-inorganic hybrid materials and indicates these organic-inorganic hybrid compounds are promising luminescent materials for lighting or displays.

Three new low-dimensional organic inorganic hybrid metal halides: Syntheses, structures and properties

It is well known that organic inorganic hybrid metal halides have been excellent materials in the field of luminescence. So far, organic-inorganic Pb(Ⅱ) halide hybrids materials have been extensively studied for their excellent optical properties. However, the toxicity of lead may generate additional pollution. It is important to develop new lead-free halide hybrids. In this work, three new organic inorganic hybrid metal halides, namely [(C4H10NO)Ag2I3] (1), [(C4H10NO)2CuI2.5]·0.5I·0.5H2O (2) and [(C4H9NO)2CdI2] (3) were synthesized under mild conditions. Compounds 1 and 2 display different one dimensional inorganic chains surrounded by organic amine cations, while compound 3 shows a zero dimensional structure. Their luminescent and optical properties were investigated in detail. The result suggests that these three compounds are potential optical materials.

The effect of solvent on the formation of low-dimensional metal halides and their self-trapped exciton emission

Low-dimensional organic–inorganic hybrid metal halides, with broadband luminescence, have attracted much attention for optoelectronic applications due to their rich in structural diversity and solution processibility. However, it is still unclear about how the solvent molecules influence the optoelectronic properties of the solution processed low-dimensional metal halides. Here, we prepared five different antimony-based crystal structures, [SbCl6]3- as the metal halide octahedron and 4, 4-difluoropiperidine (DFPD+) as organic cation, by using different solvents: hydrochloric acid (HCl) aqueous solution and four organic solvents (dimethylformamide (DMF), methanol (MeOH), acetonitrile (ACN) and dimethylacetamide (DMAC)). We revealed the relation between their crystal structures and optical properties, and we found the participation of organic molecules in the crystal structure causes significant lattice distortions, which is beneficial for achieving self-trapped exciton (STE) emission. Among them, (DFPD)6SbCl9·2DMAC exhibits a remarkable photoluminescence (PL) quantum yield of approximately 90 %. The STE dynamics in (DFPD)6SbCl9·2DMAC were characterized by femtosecond transient absorption and time-resolved PL spectroscopies. Simultaneously, this study also provides new directions for expanding the application of low-dimensional luminescent metal halides: in addition to UV-LEDs, efficient and rapid detection of methanol or acetonitrile can be achieved using the raw materials, while also realizing the potential application of multi-level optical anti-counterfeiting.

Revealing the Structure-Luminescence Relationship in Robust Sn(IV)-Based Metal Halides by Sb3+ Doping.

Low-dimensional hybrid metal halides are an emerging class of materials with highly efficient photoluminescence (PL), but the problems of poor stability remain challenging. Sn(IV)-based metal halides show robust structure but exhibit poor PL properties, and the structure-luminescence relationship is elusive. Herein, two Sn(IV)-based metal halides (compounds 1 and 2) with the same constituent ((C6H16N2)SnCl6) but different crystal structures have been prepared, which however show poor PL properties at room temperature due to the absence of active ns2 electrons. To improve materials' PL properties, Sb3+ with active 5s2 electrons was embedded into the lattice of Sn4+-based hosts. As a result, efficient emissions were achieved for Sb3+-doped compounds 1 and 2 with a maximum PL efficiency of 14.28 and 62%, respectively. Experimental and calculation results reveal that the smaller distorted lattice structure of the host could result in the blueshift of the emission from Sb3+. Thus, a tunable color from red to orange was realized. Benefiting from the broadband efficient emission from Sb3+-doped compound 2, an efficient white light-emitting diode with a high color rendering index of up to 92.3 was fabricated to demonstrate its lighting application potential. This work promotes the understanding of the influence of robust Sn(IV)-based host lattice on the PL properties of Sb3+, advancing the development of environmentally friendly, low-cost, and high-efficiency Sn(IV)-based metal halides.

Blue light emissive zero-dimensional hybrid cadmium bromide as fluorescence sensor toward benzaldehyde

Organic-inorganic hybrid low-dimensional metal halides have been widely studied as a new class of luminescence materials due to abundant structural diversity and intriguing photophysical property. Herein, we explored two new Cd-based 0D halides of [BHEPZ]CdBr4 (BHEPZ = 1,4-Bis(2-hydroxyethyl) piperazine) and [EPIPZ]CdBr4 (EPIPZ = 1-ethylpiperazine) through facile wet-chemistry method. These 0D halides exhibit blue light emissions derived from radiative recombination of self-trapped excitons (STEs) based on detailed spectroscopy investigations. More interestingly, [BHEPZ]CdBr4 exhibits rapid luminescence off switching toward benzaldehyde but fails in any other organic solvents. In-depth investigations demonstrate that the detection limit can fall to 2.65 ppm indicating perfect real-time fluorescent probe to detect benzaldehyde with high sensitivity and selectivity. This work enriches the cadmium halide materials and provide a new perspective for potential applications of 0D hybrid metal halides.

Tunable Emission of Low-Dimensional Organic Metal Halides by Stoichiometric Ratio and Metal Center.

Low-dimensional (LD) organic metal halides (OMHs) have a bright future due to their excellent photoelectric characteristics and unique structure. However, the synthesis and emission control of LD-OMHs are still unclear. Herein, the different dimensional (zero-dimensional (0D), one-dimensional (1D), and three-dimensional (3D)) of OMHs were obtained by the reaction of 1,4-diazabicyclo (2.2.2) octane with PbBr2 in different stoichiometric ratios. This discovery shows that the structure and properties of OMHs can be regulated while maintaining the functional organic cations of OMHs, which broadens the path for the development of functional LD-OMHs. Among them, 0D-OMH 1 and 1D-OMH 3 have narrow-band (full width at half-maximum (fwhm) = 74 nm) and broad-band (fwhm = 201 nm) emission, respectively. We found that when organic cations have no contribution to the formation of conduction band minimum and valence band maximum, and the distances between polyhedrons are larger than the van der Waals diameter of the halogen atom, the effect of phonons on exciton transitions can be reduced to achieve a narrow-band emission. Further, Cu(I)- and Mn (II)-based 0D-OMHs were synthesized, which have high photoluminescence quantum yield (PLQY) (33.97 and 47.33%, respectively). When the emitting of 0D-OMHs produced by the interaction of the metal-center and halogens, the asymmetric planar metal-halogen structure will result in a higher PLQY.

Crystal Structure and Optical Properties Characterization in Quasi-0D Lead-Free Bromide Crystals (C6H14N)3Bi2Br9·H2O and (C6H14N)3Sb3Br12.

Low dimensional organic inorganic metal halide materials have shown broadband emission and large Stokes shift, making them widely used in various fields and a promising candidate material. Here, the zero-dimensional lead-free bromide single crystals (C6H14N)3Bi2Br9·H2O (1) and (C6H14N)3Sb3Br12 (2) were synthesized. They crystallized in the monoclinic crystal system with the space group of P21 and P21/n, respectively. Through ultraviolet-visible-near-infrared (UV-vis-NIR) absorption analysis, the band gaps of (C6H14N)3Bi2Br9·H2O and (C6H14N)3Sb3Br12 are found to be 2.75 and 2.83 eV, respectively. Upon photoexcitation, (C6H14N)3Bi2Br9·H2O exhibit broad-band red emission peaking at 640 nm with a large Stokes shift of 180 nm and a lifetime of 2.94 ns, and the emission spectrum of (C6H14N)3Sb3Br12 are similar to those of (C6H14N)3Bi2Br9·H2O. This exclusive red emission is ascribed to the self-trapping exciton transition caused by lattice distortion, which is confirmed through both experiments and first-principles calculations. In addition, due to the polar space group structure and the large spin-orbit coupling (SOC) associated with the heavy elements of Bi and Br of crystal 1, an obvious Rashba effect was observed. The discovery of organic inorganic metal bromide material provides a critical foundation for uncovering the connection between 0D metal halide materials' structures and properties.

Narrow-Band Green-Emitting Hybrid Organic-Inorganic Eu (II)-Iodides for Next-Generation Micro-LED Displays.

Low-dimensional metal halide perovskites are an emerging class of light-emitting materials for LED-based displays; however, their B-site cations are confined to ns2, d5, and d10 metals. Here, the design of divalent rare earth ions at B-site is presented and a novel Eu(II)-based iodide hybrid is reported with efficient (PLQY≈98%) narrow-band (FWHM≈43nm) green emission and high thermal stability (97%@150°C). Owing to reduced lattice vibrations and shrunken average distance of Eu(II)-iodide bonds in the face-sharing 1D-structure, photoluminescence from Eu(II) 4f-5d transition appears along with elevated crystal-field splitting of 5d energy level. The Eu(II)-based iodide hybrid is further demonstrated for color-pure green phosphor-converted LEDs with a maximum brightness of ≈396000cdm-2 and photoelectric efficiency of 29.2%. High-resolution micrometer-scale light-emitting diode (micro-LED) displays (2540PPI) via the solution-processed screen is also presented. This work thus showcases a compelling narrow-band green emitter for commercial micro-LED displays.

Full-Spectrum White-Light Emission from Triple Self-Trapped Excitons in Hybrid Mixed-Metal Halides.

Low-dimensional metal halides with broadband emissions are expected to serve as downconversion luminescent materials for solid-state lighting (SSL). However, efficiently generating full-spectrum white-light emission with a high color-rendering index (CRI) in single-phase emitters remains a challenge. Here, we report a novel zero-dimensional (0D) hybrid mixed-metal halide (TPA)2CuAgI4 (TPA = tetrapropylammonium), in which individual [CuAgI4]2- dimers are completely isolated and surrounded by the organic cations TPA+. Cu+ and Ag+ share the same crystallographic site in [CuAgI4]2- dimers with the same statistical probability. Upon photoexcitation, single crystals exhibit a full-spectrum white-light emission with a full width at half-maximum (fwhm) of up to 314 nm and a high quantum efficiency of 46.8%. Detailed photophysical studies and theoretical calculations reveal that the ultra-broadband emission of (TPA)2CuAgI4 originates from the radiative recombination of red-, green-, and blue-emitting self-trapped excitons in [CuAgI4]2- dimers. In addition, (TPA)2CuAgI4 nanocrystals were successfully synthesized and exhibited optical properties similar to those of single-crystal counterparts. Finally, a prototype ultraviolet (UV)-pumped white-light-emitting diode (WLED) and a composite thin film employing this new white-light emitter produces a well-distributed full-spectrum white light with a high CRI of 91.4 and a warm correlated color temperature (CCT) of 4135 K, indicating the potential application of this white-light emitter in SSL. These results provide a new perspective for designing superior single-phase white-light emitters.

Mn(II)-Activated Zero-Dimensional Zinc(II)-Based Metal Halide Hybrids with Near-Unity Photoluminescence Quantum Yield.

As derivatives of metal halide perovskite materials, low-dimensional metal halide materials have become important materials that have attracted much attention in recent years. As one branch, zinc-based metal halides have the potential for practical applications due to their lead-free, low-toxicity and high-stability characteristics. However, pure zinc-based metal halide materials are still limited by their poor optical properties and cannot achieve large-scale practical applications. Therefore, in this work, we report an organic-inorganic hybrid zero-dimensional zinc bromide, (TDMP)ZnBr4, using transition metal Mn2+ ions as dopants and incorporating them into the (TDMP)ZnBr4 lattice. The original non-emissive (TDMP)ZnBr4 exhibits bright green emission under the excitation of external UV light after the introduction of Mn2+ ions with a PL peak position located at 538 nm and a PLQY of up to 91.2%. Through the characterization of relevant photophysical properties and the results of theoretical calculations, we confirm that this green emission in Mn2+:(TDMP)ZnBr4 originates from the 4T1 → 6A1 optical transition process of Mn2+ ions in the lattice structure, and the near-unity PLQY benefits from highly localized electrons generated by the unique zero-dimensional structure of the host material (TDMP)ZnBr4. This work provides theoretical guidance and reference for expanding the family of zinc-based metal halide materials and improving and controlling their optical properties through ion doping.

Unraveling the Origin of an Unusual Shift in the Electroluminescence of 1D CsCu2I3 Light-Emitting Diodes.

Lead-free low-dimensional copper-based metal halides are promising luminescent materials for broadband LEDs owing to their broad self-trapped exciton (STE) emission. However, recently, in 1D CsCu2I3, a discrepancy between their electroluminescence (EL) and photoluminescence (PL) has been observed. As a result, the overall output color from LEDs is significantly different than the anticipated emission. To unveil the origin of this discrepancy, here, we provide comprehensive analyses and show that the shift in the EL is caused neither by any structural/optical interactions between CsCu2I3 and electron transport layers (ETL) nor by the degradation of 1D CsCu2I3. Instead, it depends on the carrier imbalance on CsCu2I3, mainly due to the difference in the electron mobility of the ETLs and the electron density on the CsCu2I3 layer. By varying the ETLs, different colored 1D CsCu2I3 LEDs with peaks at 556, 590, and 647 nm are fabricated, and a maximum luminance of over 2000 cd/m2 is achieved for a 556 nm LED. Further, by limiting the electron mobility and injection to 1D CsCu2I3 using an insulating LiF layer at the CsCu2I3/ETL interface, more red-shifted LEDs are achieved confirming the critical role of electron density on the EL characteristics of 1D CsCu2I3.

Zero-dimensional hybrid tin halides with stable broadband light emissions.

Considering the instability and toxicity of 3D Pb-based perovskite nanocrystals, lead-free low-dimensional organic-inorganic hybrid metal halides have attracted widespread attention as potential substitutes. Herein, two new tin-based 0D halides [H4BAPP]SnBr5·Br and [H4BAPP]SnCl5·Cl·H2O (BAPP = 1,4-bis(3-aminopropyl)piperazine) were synthesized successfully based on [SnX5]3- as an emission center. Typically, [H4BAPP]SnBr5·Br and [H4BAPP]SnCl5·Cl·H2O display broadband yellow and yellow-green light emissions originating from the radiative recombination of self-trapped excitons (STEs). The photoluminescence quantum yields (PLQYs) of the two compounds were calculated to be 19.27% and 2.36%, respectively. Furthermore, the excellent chemical and thermal stability and broadband light emissions reveal their potential application in solid-state white lighting diodes.

Structural diversity and photoluminescence enhancement of indium-based hybrid metal halides

Low-dimensional organic-inorganic metal halides have attracted increasing attention for their diverse structure and excellent photoelectric properties. Here, we report two zero-dimensional indium-based halides, (C3H12N2)3In2Cl12·2 H2O ([C3H12N2]2+ is N-methylethylenediamine cation) with space group of P-1 and (C3H12N2)2InCl7 with space group of P21/c. Upon UV excitation, 1 %Sb doped (C3H12N2)3In2Cl12·2 H2O exhibits luminescence centering at 588 nm with a full width at half-maximum of 149 nm (0.527 eV), as well as a large Stokes shift of 262 nm (1.69 eV) with photoluminescence quantum yields as high as 56 %. The broad emission originates from the electron transitions of the Sb3+ 5s2 lone pair. 1 %Sb doped (C3H12N2)3In2Cl12·2 H2O exhibits more intense, broader emission and larger Stokes shift than that of 1 %Sb doped (C3H12N2)2InCl7 which is due to that the crystalline water increases the hydrogen bonding and leading to more distorted [SbCl6]3- octahedra. This work unveiled the relationship between structure and photoluminescence properties, and provide new types of organic-inorganic metal halides for potential application in light-emitting diodes.

Broadband Near-Infrared Emission from 0D Hybrid Copper Halides.

Metal halides have attracted increasing attention owing to their outstanding optoelectronic properties and tunable emission characteristics. Among these, low-dimensional metal halides have emerged as a novel and efficient luminescent material, primarily attributed to their broad spectral emission induced by self-trapped excitons (STEs). However, achieving highly efficient deep red and near-infrared (NIR) emission in metal halides remains a challenge. In this study, we report a novel zero-dimensional (0D) copper-based metal halide [Na2(DMSO)8]Cu4Br6 as the NIR light source, which exhibits a full width at half-maximum (FWHM) of 195 nm peaking at 685 nm, an impressive quantum efficiency of 68% and a large Stokes shift of 299 nm. Through comprehensive spectral analysis and meticulous data calculations, we substantiate that the emission originates from STEs formed within the 0D structure. Furthermore, we demonstrate the potential application of [Na2(DMSO)8]Cu4Br6 as an invisible light source in night vision by combining it with a commercially available 365 nm ultraviolet (UV) chip. This work not only enriches the family of low-dimensional metal halide materials but also inspires the potential of low-dimensional metal halides in night vision applications.

Unveiling the Structure-Luminescence-Stability relationship in 5s2-Based Antimony halides toward High-Performance emitters

Emerging low-dimensional metal halides have attracted enormous research interests due to their prominent photoluminescence (PL) properties and extensive application potentials. However, the systematic discussion on the structure-luminescence-stability relationship is still lacking. Herein, a series of novel lead-free metal halides are developed to unveil the underlying relationship. The as-synthesized (C6H5NH3)6SbCl9·H2O single crystal is structurally unstable that would spontaneously transform into (C6H5NH3)3ClSbCl5·H2O in the mother liquor, due to the strong antibonding Sb-5s2 lone pair with a spherical distribution in highly symmetrical geometry. To suppress this effect and stabilize the metastable phase, In3+ without ns electrons is introduced into the lattice of (C6H5NH3)6SbCl9·H2O, as a result, the changed coordination environment, including band structure, lattice constant and intermolecular electronic interaction, not only inhibits the structure transformation, but also leads to an enhanced PL efficiency (83.37 %) at ∼ 600 nm. This work promotes the understanding of structure-luminescence-stability relationship in organic–inorganic materials, and provides a new insight for further searching for high-performance lead-free perovskite luminescent materials.