Sunlike White-Light-Emitting Diodes Based on Zero-Dimensional Organic Metal Halide Hybrids

Solution Processed Bilayer Metal Halide White Light Emitting Diodes

Metal halide perovskites and perovskite-related organic metal halide hybrids (OMHHs) have recently emerged as a new class of luminescent materials for light emitting diodes (LEDs), owing to their unique and remarkable properties, including near-unity photoluminescence quantum efficiencies, highly tunable emission colors, and low temperature solution processing. While substantial progress has been made in developing monochromatic LEDs with electroluminescence across blue, green, red, and near-infrared regions, achieving highly efficient and stable white electroluminescence from a single LED remains a challenging and under-explored area. Here, a facile approach to generating white electroluminescence is reported by combining narrow sky-blue emission from metal halide perovskites and broadband orange/red emission from zero-dimensional (0D) OMHHs. For the proof of concept, utilizing TPPcarz+ passivated two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) as sky blue emitter and 0D TPPcarzSbBr4 as orange/red emitter (TPPcarz+ = triphenyl (9-phenyl-9H-carbazol-3-yl) phosphonium), white LEDs (WLEDs) with a solution processed bilayer structure have been fabricated to exhibit a peak external quantum efficiency (EQE) of 4.8% and luminance of 1507 cd m-2 at the Commission Internationale de L'Eclairage (CIE) coordinate of (0.32, 0.35). This work opens a new pathway for creating highly efficient and stable WLEDs using metal halide perovskites and related materials.

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.

A Luminescent Hybrid Bimetallic Halide Family with Solvent-Coordinated Rare Earth and Alkaline Earth Metals

Hybrid metal halides are an extraordinary class of optoelectronic materials with extensive applications. To further diversify and study the in-depth structure-property relations, we report here a new family of 21 zero-dimensional hybrid bimetallic chlorides with the general formula A(L)n[BClm] (A=rare earth (RE), alkaline earth metals and Mn; L=solvent ligand; and B=Sb, Bi and Te). The RE(DMSO)8[BCl6] (RE=La, Ce, Sm, Eu, Tb, and Dy; DMSO=dimethyl sulfoxide) series shows broadband emission attributed to triplet radiative recombination from Sb and Bi, incorporating the characteristic emission of RE metals, where Eu(DMSO)8[BiCl6] shows a staggering PL quantum yield of 94 %. The pseudo-octahedral [SbCl5] with Cl vacancy in AII(DMSO)6[SbCl5] (AII=Mg, Ca and Mn) and the square pyramidal [SbCl5] in AII(TMSO)6[SbCl5] (TMSO=tetramethylene sulfoxide) enhance the stereoactive expression of the 5 s2 lone pairs of Sb3+, giving rise to the observation of dual-band emission of singlet and triplet emission, respectively. A series of Te(IV) analogues have been characterized, showing blue-light-excitable single-band emission. This work expands the materials space for hybrid bimetallic halides with an emphasis on harnessing the RE elements, and provides important insights into designing new emitters and regulating their properties.

Excitation-Selective and Double-Emissive Lead-Free Binary Hybrid Metal Halides for White Light-Emitting Diode and X-Ray Scintillation

Zero-dimensional (0D) organic metal halides comprising heterogeneous metal cations in single phase can achieve multiple luminous emissions enabling them toward multifunctional light-emitting applications. Herein, A novel single crystal of (C8H20N)4SbMnCl9 containing two luminescent centers of [SbCl5]2- pentahedrons and [MnCl4]2- tetrahedrons is reported. The large distance between Sb-Sb, Mn-Mn, and Sb-Mn as well as theory calculation indicate negligible interaction between individual centers, thus endowing (C8H20N)4SbMnCl9 with excitation-dependable and efficient luminescence. Under near-UV excitation, only orange emission originates from self-trapped excitons recombination in [SbCl5]2- pentahedron occurs with photoluminescence quantum yield (PLQY) of 91.5%. Under blue-light excitation, only green emission originating from 4T1-6A1 transition of Mn2+ in [MnCl4]2- tetrahedrons occurs with PLQY of 66.8%. Interestingly, upon X-ray illumination, both emissions can be fully achieved due to the high-energy photon absorption. Consequently, (C8H20N)4SbMnCl9 is employed as phosphors to fabricate white light-emitting diodes optically pumped by n-UV chip and blue-chip thanks to its excitation-dependable property. Moreover, it also shows promising performance as X-ray scintillator with low detection limit of 60.79 nGyair S-1, steady-state light yield ≈54% of commerical scintillaotr LuAG:Ce, high resolution of 13.5 lp mm-1 for X-ray imaging. This work presents a new structural design to fabricate 0D hybrids with multicolor emissions.

The luminescent principle and sensing mechanism of metal-organic framework for bioanalysis and bioimaging

Metal-organic frameworks (MOFs) porous material have obtained more and more attention during the past decade. Among various MOFs materials, luminescent MOFs with specific chemical characteristics and excellent optical properties have been regarded as promising candidates in the research of cancer biomarkers detection and bioimaging. Therefore, the latest advances and the principal biosensing and imaging strategies based on the luminescent MOFs were discussed in this review. The effective synthesis methods of luminescent MOFs were emphasized firstly. Subsequently, the luminescent principle of MOFs has been summarized. Furthermore, the luminescent MOF-based sensing mechanisms have been highlighted to provide insights into the design of biosensors. The designability of LMOFs was suitable for different needs of biorecognition, detection, and imaging. Typical examples of luminescent MOF in the various cancer biomarkers detection and bioimaging were emphatically introduced. Finally, the future outlooks and challenges of luminescent MOF-based biosensing systems were proposed for clinical cancer diagnosis.

Mapping Uncharted Lead-Free Halide Perovskites and Related Low-Dimensional Structures

Research on perovskites has grown exponentially in the past decade due to the potential of methyl ammonium lead iodide in photovoltaics. Although these devices have achieved remarkable and competitive power conversion efficiency, concerns have been raised regarding the toxicity of lead and its impact on scaling up the technology. Eliminating lead while conserving the performance of photovoltaic devices is a great challenge. To achieve this goal, the research has been expanded to thousands of compounds with similar or loosely related crystal structures and compositions. Some materials are "re-discovered", and some are yet unexplored, but predictions suggest that their potential applications may go beyond photovoltaics, for example, spintronics, photodetection, photocatalysis, and many other areas. This short review aims to present the classification, some current mapping strategies, and advances of lead-free halide double perovskites, their derivatives, lead-free perovskitoid, and low-dimensional related crystals.

A 0D hybrid lead-free halide with near-unity photoluminescence quantum yield toward multifunctional optoelectronic applications

Zero-dimensional (0D) hybrid metal halides have emerged as highly efficient luminescent materials, but integrated multifunction in a structural platform remains a significant challenge. Herein, a new hybrid 0D indium halide of (Im-BDMPA)InCl6·H2O was designed as a highly efficient luminescent emitter and X-ray scintillator toward multiple optoelectronic applications. Specifically, it displays strong broadband yellow light emission with near-unity photoluminescence quantum yield (PLQY) through Sb3+ doping, acting as a down-conversion phosphor to fabricate high-performance white light emitting diodes (WLEDs). Benefiting from the high PLQY and negligible self-absorption characteristics, this halide exhibits extraordinary X-ray scintillation performance with a high light yield of 55 320 photons per MeV, which represents a new scintillator in 0D hybrid indium halides. Further combined merits of a low detection limit (0.0853 μGyair s-1), ultra-high spatial resolution of 17.25 lp per mm and negligible afterglow time (0.48 ms) demonstrate its excellent application prospects in X-ray imaging. In addition, this 0D halide also exhibits reversible luminescence off-on switching toward tribromomethane (TBM) but fails in any other organic solvents with an ultra-low detection limit of 0.1 ppm, acting as a perfect real-time fluorescent probe to detect TBM with ultrahigh sensitivity, selectivity and repeatability. Therefore, this work highlights the multiple optoelectronic applications of 0D hybrid lead-free halides in white LEDs, X-ray scintillation, fluorescence sensors, etc.

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.

Electronic structure study of dual-doped II-VI semiconductor quantum dots towards single-source white light emission

Single-source white light emitting colloidal semiconductor quantum dots (QDs) is one of the most exciting and promising high-quality solid-state light sources to meet the current global demand for sustainable resources. While most of the previous methods involve dual (green-red) emissive nanostructures coated on blue LEDs to achieve white light, this work describes a single-source white light emitter of robust and superior quality using dual-doping. A modified synthesis method for intense white light emitting Cu, Mn dual-doped ZnSe QDs is engineered such that the extent of doping and concentration of ligands can alter their electronic structures. This is then customized to obtain various types of white light emissions ranging from warm white to cool white. Further, the composition-driven change in the electronic structure of the host QDs is exploited to achieve emission tunability over the entire visible range.

Enhanced stability and complex phase behaviour of organic-inorganic green-emitting ionic manganese halides

Light-emitting materials based on earth-abundant metals, such as manganese hold great promise as emitters for organic lighting devices. In order to apply such emitter materials and, in particular, to overcome the problem of self-quenching due to cross-relaxation, we investigated a series of tetrabromidomanganate ([MnBr₄]^2-) salts with bulky tetraalkylphosphonium counter cations [P_nnn]⁺, namely [P_nnnn]₂[MnBr₄] (n = 4 (1), 6 (2) and 8 (3)), which can be obtained by a straightforward reaction of the respective phosphonium bromide and MnBr₂. Variation of the cation size allows control of the properties of the resulting ionic materials. 1 and 3 qualify as ionic liquids (ILs), where 1 features a melting point of 68 °C, and 3 is liquid at room temperature and even at very low temperatures. Furthermore, 1 and 2 show the formation of higher-ordered thermotropic mesophases. For 1 a transition to a thermodynamically metastable smectic liquid crystalline phase can be observed at room temperature upon reheating from the metastable glassy state; 2 appears to form a plastic crystalline phase at ∼63 °C, which persists up to the melting point of 235 °C. The photoemission is greatly affected by phase behaviour and ion dynamics. A photoluminescence quantum yield of 61% could be achieved, by balancing the increase in Mn²⁺-Mn²⁺ separation and reducing self-quenching through increasingly large organic cations which leads to adverse increased vibrational quenching. Compared to analogous ammonium compounds, which have been promoted as ̈inorganic hybrid perovskites̈, the phosphonium salts show superior performance, with respect to photoluminescent quantum yield and thermal and air/humidity stability. As the presented compounds are not sensitive to the atmosphere, in particular moisture, and show strong visible electroluminescence in the green region of light, they are important emitter materials for use in organic light-emitting devices.

Synthetic-Method-Dependent Antimony Bromides and Their Photoluminescent Properties

Recently, excellent optical properties of low-dimensional organic-inorganic metal halides, stemming from their tunable structure and optoelectronic properties, have been demonstrated. The synthetic method is critical because it is highly related to the structure and properties of the halide. Herein, we obtain two different antimony bromides, (Bmpip)₂SbBr₅ and (Bmpip)₃Sb₂Br₉, which both possess the P2₁/c space group having different crystal structures, and this confirms the important influence of synthesis on the single-crystal structure. (Bmpip)₂SbBr₅ contains Bmpip⁺ and [SbBr₅]^2- pyramids, and (Bmpip)₃Sb₂Br₉ consists of Bmpip⁺ and Sb-based dimers [Sb₂Br₉]^3-. Under 400 nm excitation, (Bmpip)₂SbBr₅ exhibits a 640 nm orange emission with a quantum yield of ∼11.5% owing to Sb 5s² electron luminescence. A diode was fabricated by (Bmpip)₂SbBr₅ and commercial phosphors and showed a high color render index of 92. Our work reveals the effect of the preparation method on the crystal structure. A luminescent material was finally identified.

Large Spectral Shift of Mn2+ Emission Due to the Shrinkage of the Crystalline Host Lattice of the Hexagonal CsCdCl3 Crystals and Phase Transition

All-inorganic halide perovskite crystals are considered excellent optical host lattices for various dopants to obtain wavelength-tunable emissions with ultra-broad bands even over a wide spectral range. Here, a series of Mn²⁺-doped bulk ligand-free CsCdCl₃ (CCC) perovskite crystals with a hexagonal shape and size of about 1 millimeter (mm) have been prepared by a facile hydrothermal method. These CCC:Mn²⁺ (CCC:Mn) crystals emit the representative orange-red photoluminescence (PL) of Mn²⁺ (⁴T₁(G)-⁶A₁(S)) in the centers of hexagonal octahedrons coordinated with six Cl^- ions. A fine-tuning of the Mn²⁺ concentration from 1 to 50 mol % Cd²⁺ induces a substantial red shift of emission spectra from 570 to 630 nm due to the shrinkage of the crystalline host lattice, and the maximum intensity of emission is achieved at 20 mol % Mn²⁺ doping. A further increase in the Mn²⁺ concentration causes a decrease of the PL intensity due to the phase transition from CCC to CsMnCl₃·2H₂O (CMCH). The strong excitation bands at 360, 370, 420, and 440 nm can make the excitation of the emissive CCC:Mn crystals possible with ultraviolet (UV) and blue chips for application in white light-emitting diodes (WLEDs). The similarity of the Mn²⁺-concentration-dependent emission spectra excited by various wavelengths indicates that there is only one type of site for Mn²⁺ occupation in CCC.

Water-Molecule-Induced Emission Transformation of Zero-Dimension Antimony-Based Metal Halide

Low-dimensional organic-inorganic metal halides have recently emerged as a class of promising luminescent materials. However, the intrinsic toxicity of lead would strongly hamper future application. Herein, we synthesized a new type of lead-free zero-dimensional (0D) antimony-based organic-inorganic metal halide single crystals, (PPZ)₂SbCl₇·5H₂O (PPZ = 1-phenylpiperazine), which features a broadband emission at 720 nm. Ultrafast transient absorption and temperature-dependent photoluminescence (PL) spectra are combined to investigate the PL mechanism, revealing that self-trapped exciton recombination was involved. Furthermore, it is interesting that (PPZ)₂SbCl₇·5H₂O material shows reversible PL emission transformation between red light (720 nm) and yellow light (590 nm) as water molecules are inserted or removed from the lattice. Such reversible emission transformation phenomenon renders the (PPZ)₂SbCl₇·5H₂O as a potential low-cost water sensing material.

Highly Efficient Light-Emitting Diodes Based on an Organic Antimony(III) Halide Hybrid

As low-dimensional lead-free hybrids with higher stability and lower toxicity than those of three-dimensional lead perovskites, organic antimony(III) halides show great application potential in opt-electronic field owing to diverse topologies along with exceptional optical properties. We report herein an antimony(III) hybrid (MePPh₃ )₂ SbCl₅ with a zero-dimensional (0D) structure, which exhibits brilliant orange emission peaked at 593 nm with near-unity photoluminescent quantum yield (99.4 %). The characterization of photophysical properties demonstrates that the broadband emission with a microsecond lifetime (3.24 μs) arises from self-trapped emission (STE). Electrically driven organic light-emitting diodes (OLEDs) based on neat and doped films of (MePPh₃ )₂ SbCl₅ were fabricated. The doped devices show significant improvement in comparison to non-doped OLEDs. Owing to the much improved surface morphology and balanced carrier transport in light-emitting layers of doped devices, the peak luminance, current efficiency (CE) and external quantum efficiency (EQE) are boosted from 82 cd m^-2 to 3500 cd m^-2 , 1.1 cd A^-1 to 6.8 cd A^-1 , and 0.7 % to 3.1 % relative to non-doped devices, respectively.

Construction of Robust Cadmium-Free Cu-In-Zn-S Nanocrystals and Polyfluorene Derivatives Hybrid Emissive Layer for Stable Electroluminescent White Light-Emitting Devices

Combination of the merit of inorganic nanocrystals (NCs) and solution-processed conjugated polymer is a convenient strategy to obtain stable and efficient electroluminescent white-light-emitting diodes (el-WLEDs). In this work, an el-WLED was fabricated on the basis of Cd-free Cu-In-Zn-S (CIZS)/ZnS NCs blending with polyfluorene derivative poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF), which exhibited a stable white light emission with a color rendering index value of 85. Meanwhile, it had a stable spectrum under high voltage due to the extremely weak energy transfer between PODPF and CIZS/ZnS NCs. To further improve the device performance, PC₉O₄ was used to replace PODPF, which presented better solubility and smoother film-forming properties. Thus, the maximum external quantum efficiency (EQE) of the optimized el-WLED was increased by 221% while maintaining a stable spectrum under high voltage. This work may provide a great foundation on color mixing cadmium-free el-WLEDs.

Reversible Luminescent Vapochromism of a Zero-Dimensional Sb3+-Doped Organic-Inorganic Hybrid

Photoactive metal ions doping is an efficient way to modulate the photophysical properties of perovskite. Herein, we report a zero-dimensional (0D) InCl₆(C₄H₁₀SN)₄·Cl:Sb³⁺ by doping Sb³⁺ into InCl₆(C₄H₁₀SN)₄·Cl, which undergoes a significant enhancement of the emission peak at 550 nm with photoluminescence quantum yield boosting from 20% to 90%. Interestingly, a red-shifted emission is observed on InCl₆(C₄H₁₀SN)₄·Cl:Sb³⁺ upon exposure to ethanol and DMF vapor with the emission peak red-shifted from 550 to 580 and 600 nm, respectively. Furthermore, the transformation is reversed after drying the vapor-exposed InCl₆(C₄H₁₀SN)₄·Cl:Sb³⁺ at ambient conditions. Detailed characterizations reveal that the crystal packing and structure distortion account for the reversible luminescent vapochromism. Thanks to the superior stability and feasible transformation of InCl₆(C₄H₁₀SN)₄·Cl:Sb³⁺ at ambient conditions, a DMF sensor was fabricated by coating the mixture of InCl₆(C₄H₁₀SN)₄·Cl:Sb³⁺ and PMMA into patterned substrate, which exhibits an obvious luminescent change upon release and uptake of DMF and excellent stability and producibility in several cycles.

Co-luminescence in a zero-dimensional organic-inorganic hybrid antimony halide with multiple coordination units

Zero-dimensional (0D) organic-inorganic hybrid metal halides (OIMHs) containing multiple halometallate species (HMSs) have received extensive attention due to their capability to achieve multifunctional photophysical characteristics. Herein we report a lead-free 0D-OIMH compound, namely [Emim]8[SbCl6]2[SbCl5] (1, Emim = 1-ethyl-3-methylimidazolium), which is the first crystal containing two distinct mononuclear [SbXn]3-n units in one single structure. The optical absorption, temperature/excitation-variable photoluminescence (PL) and PL decay were studied. 1 exhibits a broad emission centered at 577 nm, which is analyzed to be a combination of the emissions from [SbCl6]3- and [SbCl5]2-. The structural effects including SbSb distances and polyhedral distortion of [SbXn]3-n on the PL of antimony-based 0D-OIMHs are discussed in detail. This work would provide guidance for constructing Sb-based 0D OIMHs composed of multiple halometallate species.

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 .

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.

Wide range zero-thermal-quenching ultralong phosphorescence from zero-dimensional metal halide hybrids

Materials with ultralong phosphorescence have wide-ranging application prospects in biological imaging, light-emitting devices, and anti-counterfeiting. Usually, molecular phosphorescence is significantly quenched with increasing temperature, rendering it difficult to achieve high-efficiency and ultralong room temperature phosphorescence. Herein, we spearhead this challenging effort to design thermal-quenching resistant phosphorescent materials based on an effective intermediate energy buffer and energy transfer route. Co-crystallized assembly of zero-dimensional metal halide organic-inorganic hybrids enables ultralong room temperature phosphorescence of (Ph4P)2Cd2Br6 that maintains luminescent stability across a wide temperature range from 100 to 320 K (ΔT = 220 °C) with the room temperature phosphorescence quantum yield of 62.79% and lifetime of 37.85 ms, which exceeds those of other state-of-the-art systems. Therefore, this work not only describes a design for thermal-quenching-resistant luminescent materials with high efficiency, but also demonstrates an effective way to obtain intelligent systems with long-lasting room temperature phosphorescence for optical storage and logic compilation applications.

Efficient Lone-Pair-Driven Luminescence: Structure-Property Relationships in Emissive 5s2 Metal Halides

Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides.

The Rb7 Bi3-3x Sb3x Cl16 Family: A Fully Inorganic Solid Solution with Room-Temperature Luminescent Members

Low-dimensional ns2 -metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb2+ or unstable Sn2+ , and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb7 Sb3 Cl16 phase, comprised of isolated [SbCl6 ]3- octahedra and edge-sharing [Sb2 Cl10 ]4- dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K-1 at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi3+ in the Rb7 Bi3-3x Sb3x Cl16 (x≤1) family, we present the edge-shared [Sb2 Cl10 ]4- dimer as a design principle for Sb-based luminescent materials.

Supramolecular Approach for Fine-Tuning of the Bright Luminescence from Zero-Dimensional Antimony(III) Halides

Halides of ns² metal ions have recently regained broad research interest as bright narrowband and broadband emitters. Sb(III) is particularly appealing for its oxidative stability (compared to Ge²⁺ and Sn²⁺) and low toxicity (compared to Pb²⁺). Square pyramidal SbX₅ anion had thus far been the most common structural motif for realizing high luminescence efficiency, typically when cocrystallized with an organic cation. Luminescent hybrid organic-inorganic halides with octahedral coordination of Sb(III) remain understudied, whereas fully inorganic compounds show very limited structural engineerability. We show that the host-guest complexation of alkali metal cations with crown ethers fosters the formation of zero-dimensional Sb(III) halides and allows for adjusting the coordination number (5 or 6). The obtained compounds exhibit bright photoluminescence with quantum yields of up to 89% originating from self-trapped excitons, with emission energies, Stokes shifts, and luminescence lifetimes finely-adjustable by structural engineering. A combination of environmental stability and strong, intrinsic temperature-dependence of the luminescence lifetimes in the nanosecond-to-microsecond range nominate these compounds as highly potent luminophores for remote thermometry and thermography owing to their sensitivity range of 200-450 K and high specific sensitivities of 0.04 °C^-1.

Room Temperature Synthesis of All Inorganic Lead-Free Zero-Dimensional Cs4SnBr6 and Cs3KSnBr6 Perovskites

Lead halide perovskites are excellent candidates for photoelectronic and photovoltaic applications, but the toxicity from lead is extremely concerning. Recently, Sn-based zero-dimensional lead-free perovskites synthesized using solid-state reaction techniques have become a new focus in the field. Here, we report a simple room temperature antisolvent method for the synthesis of all inorganic lead-free green emissive Cs₄SnBr₆ (emission at 524 nm) and cyan emissive Cs₃KSnBr₆ (emission at 500 nm) zero-dimensional perovskites. Their photoluminescence quantum yields reach 20% and 35%, respectively. In addition, they maintain their emission for 46 and 55 h in the air, respectively, compared to only 5 min of CsSnBr₃. This method provides a convenient way to do the research and apply these highly emissive perovskites.

[DMEDA]PbCl4: a one-dimensional organic lead halide perovskite with efficient yellow emission

By using a simple room temperature solution reaction, we prepared a new type of one-dimensional (1D) hybrid lead halide [DMEDA]PbCl₄. The compound gives a bright yellow emission with efficient photoluminescence quantum efficiency (PLQE) and optical stability.

Spectral-depth imaging with deep learning based reconstruction

We develop a compact imaging system to enable simultaneous acquisition of the spectral and depth information in real time. Our system consists of a spectral camera with low spatial resolution and an RGB camera with high spatial resolution, which captures two measurements from two different views of the same scene at the same time. Relying on an elaborate computational reconstruction algorithm with deep learning, our system can eventually obtain a spectral cube with a spatial resolution of 1920 × 1080 and a total of 16 spectral bands in the visible light section, as well as the corresponding depth map with the same spatial resolution. Quantitative and qualitative results on benchmark datasets and real-world scenes show that our reconstruction results are accurate and reliable. To the best of our knowledge, this is the first attempt to capture 5D information (3D space + 1D spectrum + 1D time) with a miniaturized apparatus and without active illumination.

Electroluminescent Warm White Light-Emitting Diodes Based on Passivation Enabled Bright Red Bandgap Emission Carbon Quantum Dots

The development of efficient red bandgap emission carbon quantum dots (CQDs) for realizing high-performance electroluminescent warm white light-emitting diodes (warm-WLEDs) represents a grand challenge. Here, the synthesis of three red-emissive electron-donating group passivated CQDs (R-EGP-CQDs): R-EGP-CQDs-NMe2, -NEt2, and -NPr2 is reported. The R-EGP-CQDs, well soluble in common organic solvents, display bright red bandgap emission at 637, 642, and 645 nm, respectively, reaching the highest photoluminescence quantum yield (QY) up to 86.0% in ethanol. Theoretical investigations reveal that the red bandgap emission originates from the rigid π-conjugated skeleton structure, and the -NMe2, -NEt2, and -NPr2 passivation plays a key role in inducing charge transfer excited state in the π-conjugated structure to afford the high QY. Solution-processed electroluminescent warm-WLEDs based on the R-EGP-CQDs-NMe2, -NEt2, and -NPr2 display voltage-stable warm white spectra with a maximum luminance of 5248-5909 cd m-2 and a current efficiency of 3.65-3.85 cd A-1. The warm-WLEDs also show good long-term operational stability (L/L 0 > 80% after 50 h operation, L 0: 1000 cd m-2). The electron-donating group passivation strategy opens a new avenue to realizing efficient red bandgap emission CQDs and developing high-performance electroluminescent warm-WLEDs.

Disphenoidal Zero-Dimensional Lead, Tin, and Germanium Halides: Highly Emissive Singlet and Triplet Self-Trapped Excitons and X-ray Scintillation

Low-dimensional metal halides have been researched as optoelectronic materials for the past two decades. Zero-dimensional halides of ns² elements (Sn, Pb, Sb) have recently gained attention as highly efficient broadband light emitters. These compounds comprise discrete metal halide centers, isolated by bulky organic cations. Herein, we report isostructural halide complexes of Ge(II), Sn(II), and Pb(II) with a 1-butyl-1-methyl-piperidinium cation (Bmpip), featuring unusual disphenoidal coordination with a highly stereoactive lone pair. Spectrally broad, bright emission from highly localized excitons, with quantum efficiencies of up to 75%, is observed in blue to red spectral regions for bromides (for Pb, Sn, and Ge, respectively) and extends into the near-infrared for Bmpip₂SnI₄ (peak at 730 nm). In the case of Sn(II) and Ge(II), both singlet and triplet excitonic emission bands have been observed. Furthermore, Bmpip₂SnBr₄ and Bmpip₂PbBr₄ exhibit X-ray-excited luminescence (radioluminescence) with brightness being commensurate with that of a commercial inorganic X-ray scintillator (NaI:Tl).

Air-Stable, Lead-Free Zero-Dimensional Mixed Bismuth-Antimony Perovskite Single Crystals with Ultra-broadband Emission

Lead-free zero-dimensional (0D) organic-inorganic metal halide perovskites have recently attracted increasing attention for their excellent photoluminescence properties and chemical stability. Here, we report the synthesis and characterization of an air-stable 0D mixed metal halide perovskite (C₈ NH₁₂ )₄ Bi_0.57 Sb_0.43 Br₇ ⋅H₂ O, in which individual [BiBr₆ ]^3- and [SbBr₆ ]^3- octahedral units are completely isolated and surrounded by the large organic cation C₈ H₁₂ N⁺ . Upon photoexcitation, the bulk crystals exhibit ultra-broadband emission ranging from 400 to 850 nm, which originates from both free excitons and self-trapped excitons. This is the first example of 0D perovskites with broadband emission spanning the entire visible spectrum. In addition, (C₈ NH₁₂ )₄ Bi_0.57 Sb_0.43 Br₇ ⋅H₂ O exhibits excellent humidity and light stability. These findings present a new direction towards the design of environmentally-friendly, high-performance 0D perovskite light emitters.