Synthesis, Crystal Structure and Green Luminescence in Zero-Dimensional Tin Halide (C8H14N2)2SnBr6

Toward an Ideal Light Source for Indoor Photosynthesis: Broadband Red Emission in Zero-Dimensional Hafnium-Based Metal Halide (TPP)2HfCl6·4C2H3N:Sb3

With suitable electron-phonon coupling strength, a near-unity broadband photoluminescence quantum yield (PLQY) can be achieved in organic-inorganic hybrid metal halides (OIHMHs) via self-trapped exciton (STE) emission. However, it is still challenging to obtain high-quality red emission from OIHMHs with a desirable emission wavelength and high chemical stability, which hinders their practical application in high-performance displays, plant-growth lighting, and biomedical imaging. Herein, a series of hafnium-based zero-dimensional (TPP)2HfCl6·4C2H3N (TPP: tetraphenylphosphonium) single crystals with different Sb3+ doping levels are synthesized. The Sb3+-doped (TPP)2HfCl6·4C2H3N shows dual-band red emission with a full width at half-maximum of 178 nm and a high PLQY of 91.09%. This broad dual-band emission originates from dopant-induced extrinsic free excitons and STEs. Furthermore, (TPP)2HfCl6·4C2H3N:Sb3+ was employed as a luminescence converter in a light-emitting diode (LED) for plant growth regulation. A correlated color temperature of 4055 K and a color rendering index of 82.13 were achieved upon excitation of the LED at 365 nm. These results provide fundamental perspectives on the emission behavior of Sb3+-doped OIHMHs and illustrate their promise for use in plant-growth lighting.

Organic-Inorganic Hybrid Halide X-ray Scintillator with High Antiwater Stability

In recent years, low-dimensional organic-inorganic hybrid metal halides have garnered significant attention for optoelectronic applications due to their exceptional photophysical properties, despite their persistent challenge of low stability. Addressing this challenge, our study introduces 1-[5-(trifluoromethyl)pyridin-2-yl]piperazinium (TFPP) as a cation, harvesting a novel one-dimensional hybrid cadmium-based halide semiconductor (TFPP)CdCl4, which exhibits intense blue-light emission upon UV excitation. Additionally, (TFPP)CdCl4 demonstrates a high scintillation performance under X-ray excitation, producing 16600 ± 500 photons MeV-1 and achieving a low detection limit of 0.891 μGyair s-1. Notably, (TFPP)CdCl4 showcases remarkable stability against water, intense light sources, heating, and corrosive environments, positioning it as a promising candidate for optoelectronic applications. Through a blend of experimental techniques and theoretical analyses, including density functional theory calculations, we elucidate the unique photophysical properties and structural stability of (TFPP)CdCl4. These findings significantly contribute to the understanding of low-dimensional hybrid halide semiconductors, offering valuable insights into their potential application in advanced optoelectronic devices and paving the way for further research in this field.

Multimode Luminescence Tailoring in PMA4Na(In,Sb)Cl8 Organic-inorganic Hybrid Metal Halide via Rigid Benzene Ring Induced Local Lattice Distortion

Low dimensional organic-inorganic hybrid metal halide materials have attracted extensive attention due to their superior optoelectronic properties. However, low photoluminescence quantum yields (PLQYs) caused by parity-forbidden transition hinder their further application in optoelectronic devices. Herein, a novel yellow-emitting PMA4Na(In,Sb)Cl8 (C7H10N+, PMA+) low-dimensional OIMHs single crystal with a PLQY as high as 88 % was successfully designed and synthesized, originating from the fact that the doping of Sb3+ effectively relaxes the parity-forbidden transition by strong spin-orbit (SO) coupling and Jahn-Teller (JT) interaction. The as-prepared crystal shows an efficient dual emission peaking 495 and 560 nm at low temperature, which are ascribed to different levels of 3P1→1S0 transitions of Sb3+ in [SbCl6]3- octahedral caused by JT deformation. Moreover, wide-range luminescence tailoring from cyan to orange can be achieved through adjusting excitation energy and temperature because of flexible [SbCl6]3- octahedral in the PNIC lattice. Based on a relative stiff lattice environment, the 560 nm yellow emission under 350 nm light excitation exhibits abnormal anti-thermal quenching from 8 to 400 K owing to the suppression of non-radiative transition. The multimode luminescence regulation enriches PMA4Na(In,Sb)Cl8 great potential in the field of optoelectronics such as temperature sensing, low temperature anti-counterfeiting and WLED applications.

Amine-directed synthesis, valence state control, and optical properties of two new organic-inorganic tin chlorides

Two organic-inorganic tin chlorides, namely (C9H26N3Cl)SnCl4 (1) and (C9H26N3Cl)SnCl6 (2), were prepared via valence state control using N,N,N',N'',N''-pentamethyldiethylenetriamine as a structure-directing agent. The two compounds have zero-dimensional structures crystallized in non-centrosymmetric orthorhombic space group Cmc21 and P212121, respectively. In compound 1, the divalent tin ion forms a seesaw coordination configuration with four chloride ions, whereas in compound 2, the tetravalent tin ion forms an octahedral coordination configuration with six chloride ions. The two compounds show a moderate second-harmonic generation response under 1064 nm laser irradiation. Notably, compound 2 displays a bright orange luminescence with a photoluminescence quantum yield of 19.67%. Theoretical calculations were performed to gain insights into the optical properties of the two compounds.

Efficient tunable white emission and multiple reversible photoluminescence switching in organic Tin(IV) chlorides via regulating the host lattice environment of antimony ions for multifunctional applications

The host lattice environments of Sb3+ has a great influence on its photophysical properties. Here, we synthesized three zero-dimensional organic metal halides of (TPA)2SbCl5 (1), Sb3+-doped (TPA)SnCl5(H2O)·2H2O (Sb3+-2), and Sb3+-doped (TPA)2SnCl6 (Sb3+-3). Compared with the intense orange emission of 1, Sb3+-3 has smaller lattice distortion, thus effectively suppressing the exciton transformation from singlet to triplet self-trapped exciton (STE) states, which makes Sb3+-3 has stronger singlet STE emission and further bring a white emission with a photoluminescence quantum efficiency (PLQE) of 93.4%. Conversely, the non-emission can be observed in Sb3+-2 even though it has a similar [SbCl5]2- structure to 1, which should be due to its indirect bandgap characteristics and the effective non-radiative relaxation caused by H2O in the lattice. Interestingly, the non-emission of Sb3+-2 can convert into the bright emission of Sb3+-3 under TPACl DMF solution treatment. Meanwhile, the white emission under 315 nm excitation of Sb3+-3 can change into orange emission upon 365 nm irradiation, and the luminescence can be further quenched by the treatment of HCl. Therefore, a triple-mode reversible luminescence switch of off-onI-onII-off can be achieved. Finally, we demonstrated the applications of Sb3+-doped compounds in single-component white light illumination, latent fingerprint detection, fluorescent anti-counterfeiting, and information encryption.

Band-Gap Narrowing and Electric Transport Regulation of Hybrid Perovskites via Pressure Engineering

Lead-free organic-inorganic hybrid perovskites are one class of promising optoelectronic materials that have attracted much attention due to their outstanding stability and environmentally friendly nature. However, the intrinsic band gap far from the Shockley-Queisser limit and the inferior electrical properties largely limit their applicability. Here, a considerable band-gap narrowing from 2.43 to 1.64 eV with the compression rate up to 32.5% is achieved via high-pressure engineering in the lead-free hybrid perovskite MA3Sb2I9. Meanwhile, the electric transport process changes from the initial interaction of both ions and electrons to only the contribution of electrons upon compression. The alteration in electrical characteristics is ascribed to the vibration limitation of organic ions and the enhanced orbital overlap, resulting from the reduction of the Sb-I bond length through pressure-induced phase transitions. This work not only systematically investigates the correlation between the structural and optoelectronic properties of MA3Sb2I9 but also provides a potential pathway for optimizing electrical properties in lead-free hybrid perovskites.

A Three-Dimensional Open-Framework Tin(II) Sulfate with Near-Unity Photoluminescence Quantum Yield

A new open-framework tin(II) sulfate, formulated as C4H12N2·Sn(SO4)2·H2O, was prepared under the structure-directing effect of piperazine. This compound features a 3D structure with 16-ring channels. Under ultraviolet light irradiation, it emits bright yellow luminescence with a near-unity photoluminescence quantum yield. Theoretical calculations were carried out to understand the luminescence mechanism.

Realizing efficient broadband near-infrared emission and multimode photoluminescence switching via coordination structure modulation in Sb3+-doped 0D organic metal chlorides

Recently, organic Sb(III)-based metal halides have achieved significant results in the visible light region due to their efficient emission. However, realizing efficient broadband near-infrared (NIR) emission in such materials is a great challenge. Herein, we developed three different NIR emitters via a coordination structure modulation strategy in Sb3+-doped zero-dimensional organic metal chlorides of (C20H20P)2MnCl4, (C20H20P)2ZnCl4, and (C20H20P)2CdCl4 with tetrahedral structure. More specifically, after the dopant Sb3+ is inserted into the host lattice, the coordination structures of Sb3+ ions can change from [SbCl5]2- square-pyramidal configuration to [SbCl4]- clusters, which will bring a larger lattice distortion degree to the excited state compared to the ground state, resulting in a larger Stokes shift. Thus, efficient NIR emission with near-unity photoluminescence quantum yield (PLQY) can be obtained in Sb3+-doped compounds under 365 nm excitation. Moreover, Sb3+-doped NIR emitters also show remarkable stabilities, which prompts us to fabricate NIR phosphor conversion light-emitting diodes (pc-LEDs) and demonstrate their application in night vision. More interestingly, the Sb3+-doped (C20H20P)2MnCl4 shows tunable emission characteristics, which can be tuned from green to greenish-yellow, orange, red, and NIR emission under different external stimuli, and thus we can demonstrate the applications of this compound in quintuple-mode fluorescence anti-counterfeiting and information encryption.

Broadband Green Luminescence and Phase Transition in Low-Dimensional Organic-Inorganic Hybrid Iodate

Organic-inorganic hybrid iodide systems, which can form highly ordered chromophores and uniformly oriented transition dipole moments, serve as optimal host-guest systems for the fabrication of micrometer-scale optical devices. In particular, those with low-dimensional structures can exhibit strong quantum-limited and highly localized charges, enabling the generation of high exciton energies and stable excitation emission. In this study, we report a novel instance of an organic-inorganic hybrid iodate, (C13H11N2)(IO3), which was synthesized by incorporating the optically active organic compound, 9-aminoacridine. Upon crystallization in the monoclinic space group P21/c, this compound exhibits a direct optical band gap of 2.66 eV. The incorporation of discrete organic units within the low-dimensional structures induces pronounced local charges, culminating in broadband green luminescence with a peak at 540 nm under UV excitation. This corresponds to the CIE coordinates (0.37, 0.56). A potential phase transition was inferred through a comprehensive analysis of the variable temperature structure and emission spectra. Furthermore, first-principles calculations revealed the pivotal role of organic cations in facilitating broadband luminescence.

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.

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.

Zero-Dimensional Hybrid Antimony Chloride with Near-Unity Broad-Band Orange-Red Emission toward Solid-State Lighting

Zero-dimensional (0D) hybrid metal halides are attractive owing to their distinctive structure as well as photoluminescence (PL) characteristics. To discover 0D hybrid metal halides with high photoluminescence quantum yield and good stability is of great significance for white light-emitting diodes (LEDs). Herein, a novel hybrid antimony chloride (CTP)2SbCl5 is synthesized, which shows a bright broad-band orange-red emission peaking at 620 nm under the low energy excitation (365 nm), achieving an excellent photoluminescence quantum yield of 96.8%. In addition, (CTP)2SbCl5 shows an additional emission peaking at 470 nm when excited at high energy (323 nm). PL spectra and density functional theory results demonstrate that the observed dual-band emission originates from the singlet and triplet self-trapped excitons confined in isolated [SbCl5]2- square pyramids. Moreover, (CTP)2SbCl5 presents relatively superior air stability, and the PL intensity still maintains 78% of the initial PL intensity when exposed to the air for above 2 weeks. Benefiting from high-efficiency PL emission and good stability of (CTP)2SbCl5, a stable warm white LED device with a 92.3% color rendering index was prepared by coating blue phosphor BaMgAl10O17:Eu2+, green (Sr,Ba)2SiO4:Eu2+, and orange-red (CTP)2SbCl5 on a 365 nm LED chip. This work provides an efficient luminescent material and also demonstrates the potential application of 0D hybrid antimony chloride in solid-state lighting.

Luminescent Behavior of Sb3+-Activated Luminescent Metal Halide

Metal halide perovskites have unparalleled optoelectronic properties and broad application potential and are expected to become the next epoch-making optoelectronic semiconductors. Although remarkable achievements have been achieved with lead halide perovskites, the toxicity of lead inhibits the development of such materials. Recently, Sb3+-activated luminescent metal halide perovskite materials with low toxicity, high efficiency, broadband, large Stokes shift, and emission wavelengths covering the entire visible and near-infrared regions have been considered one of the most likely luminescent materials to replace lead halide perovskites. This review reviews the synthesis, luminescence mechanism, structure, and luminescence properties of the compounds. The basic luminescence properties of Sb3+-activated luminescent metal halide perovskites and their applications in WLED, electroluminescence LED, temperature sensing, optical anti-counterfeiting, and X-ray scintillators are introduced. Finally, the development prospects and challenges of Sb3+-activated luminescent metal halide perovskites are discussed.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic-Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides

Organic-inorganic metal halides (OIMHs) have abundant optical properties and potential applications, such as light-emitting diodes, displays, solar cells, and photodetectors. Herein, we report zero-dimensional Mn-based OIMH (C₈H₂₀N)₂MnCl₄ single crystals synthesized by a simple slow evaporation method, which exhibit intense green emission at 520 nm originating from ⁴T₁-⁶A₁ transition of Mn²⁺ ions. Large organic cations in the crystal structure result in the isolated [MnCl₄]^2- tetrahedrons, and the closest Mn-Mn distance reaches 9.07 Å, which effectively inhibits the migration of excitation energy between adjacent Mn²⁺ emission centers, thus achieving a high quantum yield (∼87%) and a long photoluminescence (PL) lifetime (3.42 ms). The different optical and structural properties at low and high temperatures are revealed by temperature-dependent PL and X-ray diffraction spectra. The PL spectra and lifetimes under the heating and cooling processes indicate that the optical property transitions are reversible at 220/240 K. Our work provides a promising strategy for building multifunctional optoelectronic materials and insights into the understanding convertible photophysical properties from isomers of metal halides.

(C5N2H14)GeBr4: A 2D Organic Germanium Bromide Perovskite with Strong Orange Photoluminescence Properties

Hybrid organic-inorganic metal halide (OIMH) perovskites are regarded as potential photoluminescent (PL) materials and have attracted intensive attention. Here, we select 1-methylpiperazine as an organic component and successfully obtain a two-dimensional (2D) Ge-based OIMH perovskite, (1-mpz)GeBr₄. It features a 2D layered structure composed of distorted [GeBr₆]^4- octahedra with organic (C₅H₁₄N₂)²⁺ located between the layers. (1-mpz)GeBr₄ exhibits strong orange color under ultraviolet (UV) light and possesses good PL stability for over 2 months. The photoluminescence quantum efficiency is measured to be 7.15% at room temperature, which is the largest among all reported low-dimensional Ge-based perovskites. Experimental measurements, combined with first-principles calculations, reveal that its PL property is attributed to self-trapped excitons (STEs) from [GeBr₆]^4- groups. From the deduced structure-property relationship, Ge-based OIMH PL perovskites with good stability and high PL efficiency can be expected.

Integrated Reversible Thermochromism, High Tc , Dielectric Switch and Narrow Band Gap in One Multifunctional Ferroic

Organic-inorganic Hybrid (OIH) materials for multifunctional switchable applications have attracted enormous attention in recent years due to their excellent optoelectronic properties and good structural tunability. However, it still remains challenging to fabricate one simple OIH compound with multi-functionals properties, such as dielectric switching, thermochromic properties, semiconductor characteristics and ferroelasticity. Under this context, we successfully synthesized [2-(2-fluorophenyl)ethan-1- ammonium]₂ SnBr₆ (compound 1), which has a higher phase transition temperature of 427.7 K. Additionally, it exhibits a semiconducting property with an indirect band gap of 2.36 eV. Combining ferroelastic, narrow band gap, thermochromic, and dielectric properties, compound 1 can be considered as a rarely reported multi-functional ferroelastic material, which is expected to give inspiration for broadening the applications in the smart devices field.

Spacer Switched Two-Dimensional Tin Bromide Perovskites Leading to Ambient-Stable Near-Unity Photoluminescence Quantum Yield

Semiconductor nanostructures with near-unity photoluminescence quantum yields (PLQYs) are imperative for light-emitting diodes and display devices. A PLQY of 99.7 ± 0.3% has been obtained by stabilizing 91% Sn²⁺ in the Dion-Jacobson (8N8)SnBr₄ (8N8-DJ) perovskite with 1,8-diaminooctane (8N8) spacer. The PLQY is favored by a longer spacer molecule and out-of-plane octahedral tilting. The PLQY shows one-month ambient stability under high relative humidity (RH) and temperature. With n-octylamine (8N) spacer, Ruddlesden-Popper (8N)₂SnBr₄ (8N-RP) also shows PLQY of 91.7 ± 0.6%, but it has poor ambient stability. The 5-300 K PL experiments decipher the self-trapped excitons (STEs) where the self-trapping depth is 25.6 ± 0.4 meV below the conduction band because of strong carrier-phonon coupling. The microsecond long-lived STE dominates over the band edge (BE) peaks at lower excitation wavelengths and higher temperatures. The higher PLQY and stability of 8N8-DJ are due to the stronger interaction between SnBr₆^4- octahedra and 8N8 spacer, leading to a rigid structure.

Organic Cation-Directed Modulation of Emissions in Zero-Dimensional Hybrid Tin Bromides

Zero-dimensional hybrid metal halides (0D HMHs) are attractive due to their intriguing self-trapped exciton (STE) emission properties. However, the effect of organic cations on the emission of 0D HMHs is relatively underexplored. Herein, we report two types of 0D hybrid tin bromides, (BMe)₂SnBr₆ (BMe = C₈N₂H₁₈) and (MeH)₂SnBr₆ (MeH = C₇N₂H₁₆), which share similar structural features with different hydrogen bonding (HB) interactions between [SnBr₆]^4- anions and organic cations. The (BMe)₂SnBr₆ with weak HB interactions exhibits only STE emission, while the (MeH)₂SnBr₆ exhibits both STE and charge transfer exciton emissions owing to the strong HB interactions, resulting in an excitation-dependent emission at cryogenic conditions. Detailed structural analyses and Hirshfeld surface calculations confirm that the enhanced HB interactions are essential to obtain the multiple emissions in (MeH)₂SnBr₆.

Competitive Dual-Emission-Induced Thermochromic Luminescence in Organic-Metal Halides

Lead-free Halides, especially Mn-based ones, are preferred as hotspots in the exploration of photoluminescent materials. However, there are few reports on sensitive reversible thermochromism and switchable dual emission originating from self-trapped exciton emission in pure Mn-Based materials. Here, we report a new Mn-based hybrid material [TMPA]₂MnI₄ (TMPA = trimethylphenylammonium), which shows two emission peaks at 545 and 660 nm benefitting from the d-d orbital transition of Mn²⁺ and the generation of self-trapped excitons, respectively. Due to the different sensitivity to temperature, the stages of thermal activation and thermal quenching of the two emission types are also inconsistent, showing a certain competition relationship and dominating the emission colors in different temperature ranges, resulting in adjustable green-orange-green thermochromic luminescence from 100 to 403 K (both high and low temperatures correspond to green, and orange is displayed at near room temperature). Therefore, thermochromic luminescence can be easily achieved by controlling the temperature under the guidance of excited states. This work provides new insights into the synthesis and application of thermochromic materials. Therefore, it is certain that regulating temperature while being guided by excited states will achieve thermochromic luminescence. This research offers fresh perspectives on the development and potential of thermochromic materials.

Highly Distorted Antimony(III) Chloride [Sb2 Cl8 ]2- Dimers for Near-Infrared Luminescence up to 1070 nm

Zero-dimensional (0D) hybrid metal halides with unique compositional and structural tunability appear as an emerging class of luminescent materials, but near-infrared (NIR) emitters therein are largely unexplored to date. This study presents three novel 0D hybrid antimony chlorines with edge-sharing [Sb₂ Cl₈ ]^2- dimers, showing unusual room-temperature broadband NIR emission with the maximum emission wavelength up to 1070 nm. Photoluminescence studies and density functional theory calculation demonstrate that the emissions originate from the highly localized excitons, and that the confined [Sb₂ Cl₈ ]^2- dimers in these structures show low symmetry and a large degree of structural freedom. These hybrid antimony chlorines with [Sb₂ Cl₈ ]^2- dimers expand the range of new NIR materials in 0D metal halides.

The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond

The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). Focusing on well-characterized structures, it is shown that it is not merely charge-assisted hydrogen bonds that stabilize the inorganic frameworks, as widely assumed and well-documented, but simultaneously nitrogen-centered pnictogen bonding, and, depending on the atomic constituents of the organic cation, other non-covalent interactions such as halogen bonding and/or tetrel bonding, are also contributors to the stabilizing of a variety of materials in the solid state. We have shown that competition between pnictogen bonding and other interactions plays an important role in determining the tilting of the MX6 (X = a halogen) octahedra of metal halide perovskites in one, two and three-dimensions. The pnictogen interactions are identified to be directional even in zero-dimensional crystals, a structural feature in many engineered ordered materials; hence an interplay between them and other non-covalent interactions drives the structure and the functional properties of perovskite materials and enabling their application in, for example, photovoltaics and optoelectronics. We have demonstrated that nitrogen in ammonium and its derivatives in many chemical systems acts as a pnictogen bond donor and contributes to conferring stability, and hence functionality, to crystalline perovskite systems. The significance of these non-covalent interactions should not be overlooked, especially when the focus is centered on the rationale design and discovery of such highly-valued materials.

Integrated Afterglow and Self-Trapped Exciton Emissions in Hybrid Metal Halides for Anti-Counterfeiting Applications

0D hybrid metal halides (0D HMHs) are considered to be promising luminescent emitters. 0D HMHs commonly exhibit self-trapped exciton (STE) emissions originating from the inorganic metal halide anion units. Exploring and utilizing the emission features of the organic cation units in 0D HMHs is highly desired to enrich their optical properties as multifunctional luminescent materials. Here, tunable emissions from organic and inorganic units are successfully achieved in triphenylsulfonium (Ph₃ S⁺ )-based 0D HMHs. Notably, integrated afterglow and STE emissions with adjustable intensities are obtained in (Ph₃ S)₂ Sn_{1- x} Te_x Cl₆ (x = 0-1) via the delicate combination of [SnCl₆ ]^2- and [TeCl₆ ]^2- . Moreover, such a strategy can be readily extended to develop other HMH materials with intriguing optical properties. As a demonstration, 0D (Ph₃ S)₂ Zn_{1- x} Mn_x Cl₄ (x = 0-1) are constructed to achieve integrated afterglow and Mn²⁺ d-d emissions with high efficiency. Consequently, these novel 0D HMHs with colorful afterglow and STE emissions are applied in multiple anti-counterfeiting applications.

Organic-Inorganic Hybrid Tin Halide Single Crystals with Sulfhydryl and Hydroxyl Groups: Formation, Optical Properties, and Stability

Lead (Pb)-free halide hybrid materials have received a great deal of attention because of their potential in optoelectronic applications. However, heteroatom-based amine lead-free tin halide hybrid single crystals have not been well investigated yet. Detailed synthetic processes, growth, crystal structures, and stability of (ACH₂CH₂NH₃)₂SnBr₆ (A = OH or SH) and (BCH₂CH₂NH₃)₂SnI₄ (B = I or SH) single crystals were investigated. Interestingly, (IH₃NCH₂CH₂SSCH₂CH₂NH₃)₂HPO₃ exhibited orange-red photoluminescence (PL) at about 620 nm with an average PL lifetime of about 912 ns. (HSCH₂CH₂NH₃)₂SnI₄ single crystals exhibited a PL peak at 620 nm with an average PL lifetime of about 0.607 ns. More importantly, (HSCH₂CH₂NH₃)₂SnI₄ single crystals exhibited reversible red-black color transformations when exposed to a H₃PO₂ solution and an ambient atmosphere, which was attributed to oxidation from Sn²⁺ to Sn⁴⁺, rather than from I^- to I₃^- (I₂). The intriguing characteristics should provide guidance for further optoelectronic applications of these Pb-free halide hybrid materials.

Lead-Free Zero-Dimensional Organic-Copper(I) Halides as Stable and Sensitive X-ray Scintillators

Low-dimensional organic-metal halides are regarded as an emerging class of X-ray scintillation materials, but most of the discovered compounds are confronted with challenges of toxicity and instability. To address these challenges, we herein report two lead-free zero-dimensional (0D) hybrid halides, (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ single crystals, grown by the low-cost solution-processing method. By single-crystal X-ray diffraction refinement, the crystal structures of (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ were determined to be orthorhombic and monoclinic crystal systems, respectively. (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ show broadband orange and yellow emissions peaking at 620 and 538 nm, respectively. Different from the emission nature of the recent reported Cu-based halide hybrids, both (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ emit from excitons bound to defects featuring spin-allowed transition, enabling them to possess fast scintillation decay time of tens of nanoseconds, respectively. In particular, the (Bmpip)₂Cu₂Br₄ single crystal has a high photoluminescence quantum yield of 48.2%, a high scintillation yield of 16,000 photons/MeV, and a low detection limit of 710 nGy_air/s. Due to the combination of nontoxicity, long-term stability, and decent detection performance, (Bmpip)₂Cu₂Br₄ could be regarded as a promising X-ray scintillator.

Pure White Emission with 91.9% Photoluminescence Quantum Yield of [(C3H7)4N]2Cu2I4 out of Polaronic States and Ultra-High Color Rendering Index

Recently, cuprous halide perovskite-type materials have drawn tremendous attention for their intriguing optical properties. Here, a zero-dimensional (0D) Cu(I)-based compound of [(C₃H₇)₄N]₂Cu₂I₄ ([C₃H₇)₄N]⁺ = tetrapropylammonium cation) was synthesized by a facile solution method, a monoclinic system of P2₁/n symmetry with a Cu₂I₄^2- cluster as the confined structure. The as-synthesized [(C₃H₇)₄N]₂Cu₂I₄ exhibits bright dual-band pure white emission with a photoluminescence quantum yield (PLQY) of 91.9% and CIE color coordinates of (0.33, 0.35). Notably, this compound also exhibits an ultrahigh color rendering index (CRI) of 92.2, which is comparable to the highest value of single-component metal halides reported recently. Its Raman spectra provide a clear spectral profile of strong electron-phonon interaction after [(C₃H₇)₄N]⁺ incorporation, favoring the self-trapped exciton (STE) formation. [(C₃H₇)₄N]₂Cu₂I₄ can give dual-STE bands at the same time because of the Cu-Cu metal bond in a Cu₂I₄^2- cluster, whose populations could be scaled by temperature, together with the local dipole orientation modulation of neighboring STEs and phase transition related emission color coordinate change. Particularly, the outstanding chemical- and antiwater stability of this compound was also demonstrated. This work illustrates the potential of such cuprous halide perovskite-type materials in multifunctional applications, such as lighting in varied environments.

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.

Room Temperature Fabrication of Stable, Strongly Luminescent Dion-Jacobson Tin Bromide Perovskite Microcrystals Achieved through Use of Primary Alcohols

Lead-free two-dimensional metal halide perovskites have recently emerged as promising light-emitting materials due to their improved stability and attractive optical properties. Herein, a facile room temperature wet milling method has been developed to make Dion-Jacobson (DJ) phase ODASnBr4 perovskite microcrystals, whose crystallization was accomplished via the aid of introduced primary alcohols: ethanol, butanol, pentanol, and hexanol. Due to the strong intermolecular hydrogen bonding, the use of ethanol promoted the formation of non-doped ODASnBr4 microcrystals, with an emission peaked at 599 nm and a high photoluminescence quantum yield (PL QY) of 81%. By introducing other primary alcohols with weaker intermolecular hydrogen bonding such as butanol, pentanol, and hexanol, [SnBr6]4- octahedral slabs of the DJ perovskite microcrystals experienced various degrees of expansion while forming O-H…Br hydrogen bonds. This resulted in the emission spectra of these alcohol-doped microcrystals to be adjusted in the range from 572 to 601 nm, while keeping the PL QY high, at around 89%. Our synthetic strategy provides a viable pathway towards strongly emitting lead-free DJ perovskite microcrystals with an improved stability.

Quasi-Zero Dimensional Halide Perovskite Derivates: Synthesis, Status, and Opportunity

In recent decades, many technological advances have been enabled by nanoscale phenomena, giving rise to the field of nanotechnology. In particular, unique optical and electronic phenomena occur on length scales less than 10 nanometres, which enable novel applications. Halide perovskites have been the focus of intense research on their optoelectronic properties and have demonstrated impressive performance in photovoltaic devices and later in other optoelectronic technologies, such as lasers and light-emitting diodes. The most studied crystalline form is the three-dimensional one, but, recently, the exploration of the low-dimensional derivatives has enabled new sub-classes of halide perovskite materials to emerge with distinct properties. In these materials, low-dimensional metal halide structures responsible for the electronic properties are separated and partially insulated from one another by the (typically organic) cations. Confinement occurs on a crystal lattice level, enabling bulk or thin-film materials that retain a degree of low-dimensional character. In particular, quasi-zero dimensional perovskite derivatives are proving to have distinct electronic, absorption, and photoluminescence properties. They are being explored for various technologies beyond photovoltaics (e.g. thermoelectrics, lasing, photodetectors, memristors, capacitors, LEDs). This review brings together the recent literature on these zero-dimensional materials in an interdisciplinary way that can spur applications for these compounds. The synthesis methods, the electrical, optical, and chemical properties, the advances in applications, and the challenges that need to be overcome as candidates for future electronic devices have been covered.

Bulk assembly of a 0D organic tin(ii)chloride hybrid with high anti-water stability

A lead-free compound, (TBAC)SnCl₃ (TBAC = tetrabutylammonium chloride), with high anti-water stability was reported, which can be stable in water for 24 hours. Upon photoexcitation, this compound exhibits a green photoluminescence (PL) centered at 523 nm with a larger Stokes shift of 260 nm at room temperature (RT), stemming from self-trapped exciton (STE) emission.

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.

Temperature-Dependent Photoluminescence of Hexafluorobenzene-Intercalated Phenethylammonium Tin Iodide 2D Perovskite

Tin halide perovskites are potential alternatives of lead halide perovskites. However, the easy oxidation of Sn²⁺ to Sn⁴⁺ brings in a challenge. Recently, layered two-dimensional hybrid tin halide perovskites have been shown to partially resist the oxidation process because of the presence of hydrophobic organic molecules. Consequently, such layered hybrid perovskites are being explored for optoelectronic applications. The optical properties of layered tin halide perovskites depend on the interlayer separation and the dielectric mismatch between the organic and inorganic layers. Intercalation (insertion) of a molecular species between the layers modifies the interlayer interactions affecting the optical properties of layered hybrid perovskites. We investigated the effect of hexafluorobenzene (HFB) intercalation in phenethylammonium tin iodide [(PEA)₂ SnI₄ ] using temperature-dependent (6 K to 300 K) photoluminescence (PL). HFB intercalation increases the bandgap. A strong PL quenching is observed in pristine (PEA)₂ SnI₄ below 150 K, probably because of the presence of non-emissive states. HFB intercalation suppresses the influence of such non-emissive states resulting in an increase in PL intensity at the cryogenic temperatures. Our results highlight that a simple molecular intercalation (non-covalent interaction) into layered hybrid perovskites can significantly tailor the electronic and optical properties.

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.

Syntheses, structure and properties of a new series of organic-inorganic Hg-based halides: adjusting halogens resulted in huge performance mutations

Three new organic-inorganic hybrid perovskite (OIHP) halides, [N(CH3)4]HgCl0.63Br2.37 (I), [N(CH3)4]HgBrI2 (II) and [N(CH3)4]HgCl0.45I2.55 (III), were synthesized by a hydrothermal reaction. They feature different crystal structures, in which both II and III are isomorphic and contain a one-dimensional chain with organic cation [N(CH3)4]+ interspersed in the space, whereas II has a similar one-dimensional chain but significantly different spatial arrangement due to the enhanced hydrogen bond interaction. The experimental results show that the divergent second-order nonlinear optical (NLO) effect from Br(Cl) to I and the arrangement of anion groups change dramatically from the presence of hydrogen bonds to the absence of hydrogen bonds, leading to a sharply increased NLO response of II and III (18 and 25 times that of I) compared with that of I. Moreover, the phase matching ability disappeared and the band gap decreased significantly. Meanwhile, a high temperature phase transition was observed in II and III, which is rare in common OIHPs. All these results indicate that the regulation of halogen bonds plays a crucial role in the structural and property mutations of OIHP halides.

Acentric Organic-Inorganic Hybrid Halide [N(CH3)4]2HgBr2I2 Featuring an Isolated [HgBr2I2]2- Tetrahedron and Second-Order Nonlinearity

A new hybrid compound [N(CH₃)₄]₂HgBr₂I₂, obtained by a hydrothermal reaction, crystallized in the noncentrosymmetric space group P2₁2₁2₁. Its structure contains an isolated asymmetric [HgBr₂I₂]^2- tetrahedron with net polarization, connected by hydrogen bonds to form pseudo-one-dimensional chain structures. Moreover, its optical band gap, nonlinear optical (NLO) property, fluorescence property, and thermal property were characterized in detail. A rare high-temperature phase transition was observed in the compound. In addition, theoretical calculations were performed to elaborate the relation between electronic state, band structure, and their nonlinear optical response. These results indicate that [N(CH₃)₄]₂HgBr₂I₂ is a new potential candidate for future photoelectronic applications in fluorescence and nonlinear optics.

Highly Efficient Cool-White Photoluminescence of (Gua)3Cu2I5 Single Crystals: Formation and Optical Properties

Zero-dimensional lead-free organic-inorganic hybrid metal halides have drawn attention as a result of their local metal ion confinement structure and photoelectric properties. Herein, a lead-free compound of (Gua)₃Cu₂I₅ (Gua = guanidine) with a different metal ion confinement has been discovered, which possesses a unique [Cu₂I₅]^3- face-sharing tetrahedral dimer structure. First-principles calculation demonstrates the inherent nature of a direct band gap for (Gua)₃Cu₂I₅, and its band gap of ∼2.98 eV was determined by experiments. Worthy of note is that (Gua)₃Cu₂I₅ exhibits a highly efficient cool-white emission peaking at 481 nm, a full-width at half-maximum of 125 nm, a large Stokes shift, and a photoluminescence quantum efficiency of 96%, originating from self-trapped exciton emission. More importantly, (Gua)₃Cu₂I₅ single crystals have a reversible thermoinduced luminescence characteristic due to a structural transition scaled by the electron-phonon coupling coefficients, which can be converted back and forth between cool-white and yellow color emission by heating or cooling treatment within a short time. In brief, as-synthesized (Gua)₃Cu₂I₅ shows great potential for application both in single-component white solid-state lighting and sensitive temperature scaling.

Hybrid 0D Antimony Halides as Air-Stable Luminophores for High-Spatial-Resolution Remote Thermography

Luminescent organic-inorganic low-dimensional ns2 metal halides are of rising interest as thermographic phosphors. The intrinsic nature of the excitonic self-trapping provides for reliable temperature sensing due to the existence of a temperature range, typically 50-100 K wide, in which the luminescence lifetimes (and quantum yields) are steeply temperature-dependent. This sensitivity range can be adjusted from cryogenic temperatures to above room temperature by structural engineering, thus enabling diverse thermometric and thermographic applications ranging from protein crystallography to diagnostics in microelectronics. Owing to the stable oxidation state of Sb3+ , Sb(III)-based halides are far more attractive than all major non-heavy-metal alternatives (Sn-, Ge-, Bi-based halides). In this work, the relationship between the luminescence characteristics and crystal structure and microstructure of TPP2 SbBr5 (TPP = tetraphenylphosphonium) is established, and then its potential is showcased as environmentally stable and robust phosphor for remote thermography. The material is easily processable into thin films, which is highly beneficial for high-spatial-resolution remote thermography. In particular, a compelling combination of high spatial resolution (1 µm) and high thermometric precision (high specific sensitivities of 0.03-0.04 K-1 ) is demonstrated by fluorescence-lifetime imaging of a heated resistive pattern on a flat substrate, covered with a solution-spun film of TPP2 SbBr5 .

Role of Metal-Chloride Anions in Photoluminescence Regulations for Hybrid Metal Halides

Organic-inorganic hybrid metal halides with emissive organic cations are of great interest due to their structural diversity and interesting photophysical properties. Here, we assemble emissive organic cations (EnrofloH₂²⁺) with different metal-chloride anions (Pb₂Cl₆^2- to Bi₂Cl₁₀^4- to SnCl₆^2-) to form the new single crystal phases, and thus the photoluminescence properties of the metal halides, including Stokes shift, full width at half-maximum (FWHM), and photoluminescence quantum yield (PLQY) have been studied accordingly. (EnrofloH₂)SnCl₆·H₂O, as an example, possesses narrow FWHM and high PLQY, which are caused by the strong π-π stacking and inter- and intramolecular hydrogen bonds interactions. Compared with EnrofloH₂²⁺ cation in solution, the interactions generate a restraining effect and increase the rigid degree of EnrofloH₂²⁺ cation in the bulk single crystals. Our work clarifies the photophysical properties of the EnrofloH₂²⁺ organic cations by constructing the inter- and intramolecular interactions and boosts the further study of organic-inorganic hybrid metal halides materials with different luminescence mechanisms.

Combining Dual-Light Emissions to Achieve Efficient Broadband Yellowish-Green Luminescence in One-Dimensional Hybrid Lead Halides

In recent years, low-dimensional lead halides have emerged as some of most attractive photoelectric materials due to their intrinsic broadband emissions with a potential application in white-light emitting diodes. To achieve the desired performance, tremendous research has emphasized the modulation of inorganic components as optical centers; however, less work has paid attention to the direct contribution of the organic components. Herein, we successfully assembled two new hybrid lead halides of [H₂BPP]Pb₂X₆ (X = Br, 1, and Cl, 2) containing one-dimensional double [Pb₂X₆]^2- chains using optically active 1,3-bis(4-pyridyl)-propane (BPP) as an organic cation. Under UV-light excitation, compounds 1 and 2 exhibit broadband yellowish-green emissions, which were verified by promising photoluminescence quantum efficiencies (PLQEs) of 8.10% and 4.84%, respectively. The broadband light emissions are derived from the combination of dual higher-energy blue and lower-energy yellow light spectra, which can be attributed to the individual contributions of the organic and inorganic components, respectively, according to the time-resolved and temperature-dependent emission spectra as well as theoretical calculations. This work proves the great contribution of organic components to the photophysical properties and provides a new design strategy to realize broadband light emission by rationally combining the dual-emitting properties of different assembly blocks.

The twinned crystal structure of 1,3-phenylenedimethanaminium dibromide, C8H14Br2N2

C8H14Br2N2, monoclinic, I2/a (no. 15), a = 9.0331(9) Å, b = 13.4475(14) Å, c = 27.586(3) Å, β = 94.879(9)°, Z = 12, V = 3338.8(6) Å3, R gt (F) = 0.0582, wR ref = 0.0885, T = 290 K.

Preparation of zero-thermal-quenching tunable emission bismuth-containing phosphors through the topochemical design of ligand configuration

We report a high performance bismuth-containing phosphor with zero-thermal-quenching, which can be used for white light illumination and non-contact temperature sensing.

Recent progress of zero-dimensional luminescent metal halides

This review provides in-depth insight into the structure–luminescence–application relationship of 0D all-inorganic/organic–inorganic hybrid metal halide luminescent materials.

Multisequential reversible phase transition materials with semiconducting and fluorescence properties: (C8H18BrN)2SnBr6

A novel organic–inorganic hybrid metal halide has synthesized, namely (C8H18BrN)2SnBr6 (1), which have excellent switchable dielectric properties, narrow band gap and broadband yellow fluorescence characteristics.

Sn3B8O15: A Ternary Tin(II) Borate with Flexible [B8O18]12- Fundamental Building Block Formed by [B7O16]11- and [BO3]3- Groups

Owing to the tendency to form the glass state in growing crystals in the ternary tin(II) borate system, hitherto, very few single crystals in ternary tin(II) borate were reported. In this paper, a single crystal of Sn₃B₈O₁₅ was obtained via a high temperature solution method in a closed system. The structure features a flexible fundamental building block [B₈O₁₈]^12- constructed by one [BO₃]^3- unit and one [B₇O₁₆]^11- group that contains three hexatomic rings, which further connect to compose a two-dimensional ²_∞[B₈O₁₅] layer structure. The connection mode and flexibility of the three hexatomic B-O rings were analyzed, verifying the structural diversity of the B-O configuration. Moreover, the synthesis, crystal structure, and various characterizations were comprehensively presented. Also, theoretical calculations were employed to discuss structure-property relationships, and we use the real-space atom-cutting techniques to explain the origin of the birefringence of Sn₃B₈O₁₅.