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

Yellow-Orange Emission in Sb3+-Doped Hexakis(thiocarbamidium) Hexabromoindium(III) Tribromide

A luminescent zero-dimensional organic-inorganic hybrid indium halide (TUH)6[In1-xSbxBr6]Br3 (TU = thiourea, 0 ≤ x ≤ 0.0998) was synthesized via the solvothermal method. In structures, resolved by single-crystal X-ray diffraction, isolated distorted [InBr6]3- and [SbBr6]3- octahedra are linked to organic TUH+ cations by intermolecular N-H···Br and N-H···S hydrogen bonds. The crystals were characterized by elemental analysis, TG-DSC, powder X-ray diffraction, FTIR analysis, and steady-state absorption and photoluminescence spectroscopy. (TUH)6[In1-xSbxBr6]Br3 exhibits a broadband yellow-orange emission centered at 595-602 nm with a half-width of 141-149 nm (0.48-0.52 eV) and a large Stokes shift of 232-238 nm (1.33-1.35 eV). This emission can be attributed to the self-trapped exciton emission of triplet states of the octahedral anion [SbBr6]3- or [InBr6]3-. Two possible emission mechanisms were discussed. Doping with Sb3+ leads to a significant increase in photoluminescence quantum yield from 25.7 at x = 0 to 48.4% at x = 0.0065, when excited at 365 nm, indicating the potential use of (TUH)6[In1-xSbxBr6]Br3 compounds in the field of photonics.

Synthesis, Structure, and Optical Properties of a 0D Hybrid Organic-Inorganic Metal Halide (C5N2H14Cl)GeCl3

Due to the flexible structural tunability and excellent photoelectric performance, hybrid organic-inorganic metal halides (OIMHs) have attracted intensive attention and become a hot topic in the field of materials. It is important and necessary to explore new OIMHs and study their structure-property relationship. In this work, a new lead-free OIMH, (C5N2H14Cl)GeCl3, is synthesized by the combination of hydrothermal and solution methods. This compound features a zero-dimensional structure composed of inorganic [GeCl3]- trigonal pyramids surrounded by isolated Cl- anions and organic (C5N2H14)2+ cations. Preliminary characterization and first-principles calculations are performed to study its basic optical properties. Interestingly, (C5N2H14Cl)GeCl3 shows weak blue emission under ultraviolet excitation, and the intrinsic mechanism is discussed.

Tellurium(IV) Halide Achieving Effective Nonlinear-Optical Activity: The Role of Chiral Ligands and Lattice Distortion

Chiral organic-inorganic hybrid metal halides are a promising class of nonlinear-optical materials with unique optical properties and flexible crystal structures. However, the structures and properties of chiral hybrid tellurium halides, especially second harmonic generation (SHG), have not been reported. Here, by introducing chiral organic molecule (R/S)-methylbenzylammonium (R/S-MBA), we synthesized a pair of novel zero-dimensional (0D) chiral tellurium-based hybrid halides with noncentrosymmetric space group C2, (R/S-MBA)2TeCl6 (R/S-Cl). Single-crystal X-ray diffraction analysis and solid-state circular dichroism (CD) spectra confirm that R/S-Cl shows obvious enantiomer enrichment. Moreover, the resulting chiral products present an efficient SHG response. Interestingly, through manipulation of halogen atoms, two pairs of achiral tellurium halides, (R/S-MBA)2TeBr6 (R/S-Br) and (R/S-MBA)2TeI6 (R/S-I), were obtained, both of which crystallize in the centrosymmetric space group R3̅. It is noteworthy that R/S-I has a narrow band gap of 1.55 eV, which is smaller than that of most 0D metal halides and comparable to that of three-dimensional lead halide, showing its potential as a highly efficient light absorber.

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.

Dual Monomeric Inorganic Units Constructed Bright Emissive Zero-Dimensional Antimony Chlorides with Solvent-Induced Reversible Structural Transition

A5M2X11 and A3M2X9 families (A = monovalent organic cation; M = trivalent metal; X = halogen) are receiving increasing attention because of their combination of easy solution processability and superior ferroelectricity properties. However, synthesizing highly efficient A5M2X11 and A3M2X9-type fluorophores with multiple monomeric inorganic units and achieving their structural interconversion remains challenging. Here, we report two novel zero-dimensional (0D) antimony halides, (C10H16N)5Sb2Cl11·C2H3N (1) and (C10H16N)3Sb2Cl9 (2), which not only contain two distinct [SbXn]3-n units but also have excellent orange (590 nm) and yellow-green emission (540 nm) with high PLQY of 17.7% and 31.5%, respectively. Interestingly, a reversible structural conversion could be triggered by acetonitrile steam stimulation, accompanied by luminescence switching properties. This work not only enriches the structure of hybrid Sb-based halides but also provides the possibility of well-known A5M2X11 and A3M2X9 families as structural transformation materials.

Facile synthesis of Sb3+-doped (Bmim)2InCl5(H2O) through a grinding method for light-emitting diodes

Organic-inorganic metal hybrid halides (OIMHs) as a new kind of photoelectric material have gained much attention in recent years because of their excellent performance in solid-state lighting applications. However, the preparation of most OIMHs is complex and requires a long preparation time in addition to the solvent providing the reaction environment. This greatly limits their further applications. Here, we synthesized zero-dimensional lead-free OIMH (Bmim)₂InCl₅(H₂O) (Bmim = 1-butyl-3-methylimidazolium) by a facile grinding method at room temperature. Through Sb³⁺ doping, Sb³⁺:(Bmim)₂InCl₅(H₂O) shows a bright broadband emission centered at 618 nm under UV excitation, which could be attributed to the self-trapped exciton (STE) emission of Sb³⁺ ions. To explore their ability in the field of solid-state lighting, a white-light-emitting diode (WLED) device based on Sb³⁺:(Bmim)₂InCl₅(H₂O) with a high color rendering index of 90 was fabricated. This work enriches In³⁺-based OIMHs and provides a new direction for the simple fabrication of OIMHs.

Circularly Polarized Luminescence in Zero-Dimensional Antimony Halides: Structural Distortion Controlled Luminescence Thermometer

Materials emitting circularly polarized luminescence (CPL) have been intensively studied for their promising applications in various fields. However, developing tunable and responsive CPL materials in a wide wavelength range remains a great challenge. Here, a pair of chiral (R,R/S,S-DCDA)₃Sb₂Cl₁₂ (DCDA = dimethyl-1,2-cyclohexanediamine divalent cation) shows efficient broadband yellow emission with a photoluminescence (PL) quantum yield of 27.6% with a CPL asymmetry factor of 3 × 10^-3. The associated chiroptical activity is attributed to the efficient chiral transfer as well as the self-trapped exciton emission originating from the large distortion of the inorganic blocks. Notably, (R,R/S,S-DCDA)₃Sb₂Cl₁₂ exhibits a large red-shift emission exceeding 100 nm upon lowering temperature. An excellent linear correlation of the PL wavelength on temperature indicates that the compounds can be used as PL thermometers, which originates from a temperature-dependent linear structural distortion of the [SbCl₆] emitter. This work inspires the potential utilization of CPL-emitting materials as responsive light sources.

Effect of the Host Lattice Environment on the Expression of 5s2 Lone-Pair Electrons in a 0D Bismuth-Based Metal Halide

ns²-Metal halide perovskites have attracted wide attention due to their fascinating photophysical properties. However, achieving high photoluminescence (PL) properties is still an enormous challenge, and the relationship between the lattice environment and ns²-electron expression is still elusive. Herein, an organic-inorganic Bi³⁺-based halide (C₅H₁₄N₂)₂BiCl₆·Cl·2H₂O (C₅H₁₄N₂²⁺ = doubly protonated 1-methylpiperazine) with a six-coordinated structure has been successfully prepared, which, however, exhibits inferior PL properties due to the chemically inert expression of Bi³⁺-6s² lone-pair electrons. After reasonably embedding Sb³⁺ with 5s² electrons into the lattice of (C₅H₁₄N₂)₂BiCl₆·Cl·2H₂O, the host lattice environment induces the Sb-Cl moiety to change from the original five-coordinated to six-coordinated structure, thereby resulting in a broad-band yellow emission with a PL efficiency up to 50.75%. By utilizing the host lattice of (C₅H₁₄N₂)₂BiCl₆·Cl·2H₂O, the expression of Sb³⁺-5s² lone-pair electrons is improved and thus promotes the radiative recombination from the Sb³⁺-³P₁ state, resulting in the enhanced PL efficiency. This work will provide an in-depth insight into the effect of the local structure on the expression of Sb³⁺-5s² lone-pair electrons.

Rational Design of a Super-Alkali Compound with Reversible Photoluminescence

The zero-dimensional (0D) (H₅O₂)(C₄H₁₄N₂S₂)₂BiCl₈: Sb³⁺ single crystal is obtained by the cooling crystallization method. Surprisingly, this compound shows reversible photoluminescence (PL) upon H₅O₂⁺Cl^- removal and insertion. To be specific, the release of H₅O₂⁺Cl^- resulted in red-orange emission with a very low photoluminescence quantum yield (PLQY). While on the reuptake of it, a bright yellow emission with a nearly 10-fold increase of PLQY was observed. Density functional theory (DFT) calculations and temperature-dependent PL experiments reveal that significant [SbCl₆]^3- octahedron distortion induced by guest (H₅O₂⁺Cl^-) removal at the ground state, especially at the excited state, is responsible for the disparate PL performance. Encouragingly, we also found that (C₄H₁₄N₂S₂)₂BiCl₇: Sb³⁺ exhibits a fast response (<3 s) to dilute hydrochloric acid with naked-eye perceivable PL color changes, rendering it a potential sensing material for hydrochloric acid.

Realizing High-Efficiency Yellow Emission of Organic Antimony Halides via Rational Structural Design

Zero-dimensional (0D) organic metal halides have captured extensive attention for their various structures and distinguished optical characteristics. However, achieving efficient emission through rational crystal structure design remains a great challenge, and how the crystal structure affects the photophysical properties of 0D metal halides is currently unclear. Herein, a rational crystal structure regulation strategy in 0D Sb(III)-based metal halides is proposed to realize near-unity photoluminescence quantum yield (PLQY). Specifically, two 0D organic Sb(III)-based compounds with different coordination configurations, namely, (C₂₅H₂₂P)₂SbCl₅ and (C₂₅H₂₂P)SbCl₄ (C₂₅H₂₂P⁺ = benzyltriphenylphosphonium), were successfully obtained by precisely controlling the ratio of the initial raw materials. (C₂₅H₂₂P)₂SbCl₅ adopts an octahedral coordination geometry and shows highly efficient broadband yellow emission with a PLQY of 98.6%, while (C₂₅H₂₂P)SbCl₄ exhibits a seesaw-shaped [SbCl₄]^- cluster and does not emit light under photoexcitation. Theoretical calculations reveal that, by rationally controlling the coordination structure, the indirect bandgap of (C₂₅H₂₂P)SbCl₄ can be converted to the direct bandgap of (C₂₅H₂₂P)₂SbCl₅, thus ultimately boosting the emission intensity. Together with efficient emission and outstanding stability of (C₂₅H₂₂P)₂SbCl₅, a high-performance white-light emitting diode (WLED) with a high luminous efficiency of 31.2 lm W^-1 is demonstrated. Our findings provide a novel strategy to regulate the coordination structure of the crystals, so as to rationally optimize the luminescence properties of organic metal halides.

Luminescent Organic-Inorganic Hybrid Metal Halides: An Emerging Class of Stimuli-Responsive Materials

Luminescent organic-inorganic metal halides (OIMHs) are well known as a new materials family in recent years. Novel materials and applications of luminescent OIMHs have been explored by changing either the organic component or the metal halide species. Thereinto, the stimuli-responsive (SR) phenomena in OIMHs have drawn much attention recently, for not only their attractive application potential but also the helpfulness in understanding the stability of OIMHs to the external environment. Herein, the luminescent OIMHs that are sensitive to external stimuli including contact, pressure, mechanical grinding, light, heat, and gas molecules, are reviewed, with an emphasis on analyses of the structural change during the SR process. The applications of SR luminescent OIMHs in widespread fields, including gas sensing, information encryption, and rewritable luminescent paper are summarized. Finally, the challenges that deserve to be further explored in this research field are discussed, which provides certain guidance for the future study of SR luminescent OIMHs.

A Zero-Dimensional Organic Lead Bromide of (TPA)2PbBr4 Single Crystal with Bright Blue Emission

Blue-luminescence materials are needed in urgency. Recently, zero-dimensional (0D) organic metal halides have attractive much attention due to unique structure and excellent optical properties. However, realizing blue emission with near-UV-visible light excitation in 0D organic metal halides is still a great challenge due to their generally large Stokes shifts. Here, we reported a new (0D) organic metal halides (TPA)2PbBr4 single crystal (TPA+ = tetrapropylammonium cation), in which the isolated [PbBr4]2− tetrahedral clusters are surrounded by organic ligand of TPA+, forming a 0D framework. Upon photoexcitation, (TPA)2PbBr4 exhibits a blue emission peaking at 437 nm with a full width at half-maximum (FWHM) of 50 nm and a relatively small Stokes shift of 53 nm. Combined with density functional theory (DFT) calculations and spectral analysis, it is found that the observed blue emission in (TPA)2PbBr4 comes from the combination of free excitons (FEs) and self-trapped exciton (STE), and a small Stokes shift of this compound are caused by the small structure distortion of [PbBr4]2− cluster in the excited state confined by TPA molecules, in which the multi-phonon effect take action. Our results not only clarify the important role of excited state structure distortion in regulating the STEs formation and emission, but also focus on 0D metal halides with bright blue emission under the near-UV-visible light excitation.

Nearly one-fold enhancement in photoluminescence quantum yield for isostructural zero-dimensional hybrid antimony(III) bromides by supramolecular interaction adjustments

Zero-dimensional (0D) organic-inorganic metal halides (OIMHs) hold promise in photoluminescence properties and related applications. Thus far, the photoluminescence quantum yields (PLQYs) of the reported 0D hybrid antimony(III) bromides (HABs) are not as high as those of the chloride analogs; therefore, the improvement of PLQY is an important issue for luminescent HABs. Herein, a supramolecular interaction adjustment strategy to improve the PLQYs of HABs is proposed. Two isostructural 0D HABs that crystallize with different lattice solvent molecules, namely [EtPPh₃]₂[SbBr₅]·EtOH (1·EtOH-Br; EtPPh₃ = ethyltriphenylphosphonium; EtOH = ethanol) and [EtPPh₃]₂[SbBr₅]·MeCN (1·MeCN-Br; MeCN = acetonitrile), have been synthesized. Both of them exhibit typical self-trapped exciton (STE) photoluminescence (PL) with broad emission, a large Stokes shift and a long lifetime. They show deviation in deep-red emission peaks (655 nm vs. 661 nm) owing to the difference in the distortion level of [SbBr₅]^2- anions. Most importantly, 1·EtOH-Br exhibits a nearly one-fold enhancement in PLQY compared to 1·MeCN-Br (18.26% vs. 9.29%). Density functional theory (DFT) calculations, hydrogen bonding analysis and Hirshfeld surface analysis suggest that the PLQY enhancement is due to the structural rigidity improvement brought by hydrogen bonding adjustments between the inorganic [SbBr₅]^2- anions and solvent molecules. This work provides a new insight into the structure-property relationship study and PLQY improvement for 0D OIMHs.

A deep-red-emission antimony(III) chloride with dual-cations: extremely large Stokes shift due to high [SbCl6] distortion

Compound [C₅mim][Mim]₂[SbCl₆] (1; [C₅mim]⁺ = 1-pentyl-3-methylimidazolium; [Mim]⁺ = N-methylimidazolium) with dual cations exhibits the first case of deep-red emission in [SbCl₆]^3--based 0D OIMHs. Anion distortion due to high disequilibrium of supramolecular interactions is revealed to be responsible for the extremely large Stokes shift of 335 nm and FWHM of 210 nm in the emission.

Realizing Near-Unity Quantum Efficiency of Zero-Dimensional Antimony Halides through Metal Halide Structural Modulation

Zero-dimensional (0D) organic metal halides have attracted significant attention because of their exceptional structure tunability and excellent optical characteristics. However, controllable synthesis of a desirable configuration of metal halide species in a rational way remains a formidable challenge, and how the unique crystal structures affect the photophysical properties are not yet well understood. Here, a reasonable metal halide structural modulation strategy is proposed to realize near-unity photoluminescence quantum efficiency (PLQE) in 0D organic antimony halides. By carefully controlling the reaction conditions, both 0D (C₁₂H₂₈N)₂SbCl₅ and (C₁₂H₂₈N)SbCl₄ with different metal halide configurations can be prepared. (C₁₂H₂₈N)₂SbCl₅ with pyramid-shaped [SbCl₅]^2- species exhibits yellow emission with a near-unity PLQE of 96.8%, while (C₁₂H₂₈N)SbCl₄ with seesaw-shaped [SbCl₄]^- species is not emissive at room temperature. Theoretical calculations indicate that the different photophysical properties of these two crystals can be attributed to the different symmetries of their crystal structures. (C₁₂H₂₈N)₂SbCl₅ adopts a triclinic structure with P-1 symmetry, while (C₁₂H₂₈N)SbCl₄ possesses a monoclinic structure with P2₁/c symmetry, which has an inversion center, and thus the optical transitions between their band-edge states give a minimal dipole intensity because of their similar parity character. In addition, we also successfully synthesized (C₁₂H₂₈N)₂SbCl₅ nanocrystals for the first time, which are particularly appealing for their solution processibility and excellent optical properties. Furthermore, (C₁₂H₂₈N)₂SbCl₅ nanocrystals flexible composite film shows bright yellow emission under β-ray excitation, suggesting a strong potential of (C₁₂H₂₈N)₂SbCl₅ for β-ray detection.

Ionic indium(III) chloride hybrids incorporating a 2,2'-bipyrimidine ligand: studies on photoluminescence and structural transformation

Although luminescent indium(III) based halide perovskites have been widely investigated, the study of emissive indium(III) halide hybrids is limited. Three indium(III) chloride hybrids based on a bpym ligand were synthesized, namely [EPy]₂[InCl₄(bpym)InCl₄]·DMF (1), [EPy]₂[InCl₄(bpym)InCl₄] (2), and [BPy]₂[InCl₄(bpym)InCl₄] (3) (EPy = N-ethylpyridinium; BPy = N-butylpyridinium; bpym = 2,2'-bipyrimidine). They all exhibit a zero-dimensional structure, in which the ligand bpym interconnects two [InCl₄]^- to form a [InCl₄(bpym)InCl₄]^2- anion that is further charge-compensated by the corresponding pyridinium cations. This is the first time using bpym to coordinate with an In atom. At 298 K, 1 exhibits a weak emission at 600 nm while 2 and 3 exhibit emissions peaking at 500 nm and 540 nm, respectively. Interestingly, the DMF solvent molecule in 1 can be removed by heating, thus resulting in the structural transformation of 1 into 2 together with a photoluminescence (PL) change. Density functional theory (DFT) calculations confirm that halogen-to-ligand charge-transfer (HLCT) occurs in the emission process. To the best of our knowledge, this is the first report on PL of ionic indium(III) halide hybrids incorporating organic ligands.

Selective Luminescence Response of a Zero-Dimensional Hybrid Antimony(III) Halide to Solvent Molecules: Size-Effect and Supramolecular Interactions

Zero-dimensional (0D) metal halides with solid-state luminescence switching (SSLS) have attracted attention as sensors and luminescent anticounterfeiting. Herein, selective solvent molecule response and accordingly luminescence switching were discovered in 0D [EtPPh₃]₂[SbCl₅] (1, EtPPh₃ = ethyltriphenylphosphonium). More than a dozen kinds of solvent molecules have been tested to find out the selection rule for molecule absorption in 1, which is demonstrated to be the size effect of guest molecules. Confirmed by crystal structural analysis, only the solvents with molecular volume less than 22.3 ų could be accommodated in 1 leading to the solvatochromic photoluminescence (PL). The mechanism of solvatochromic PL was also deeply studied, which was found to be closely related to the supramolecular interactions between solvent molecules and the host material. Different functional groups of the solvent molecule can affect its strength of hydrogen bonding with [SbCl₅]^2-, which is crucial for the distortion level of [SbCl₅]^2- unit and thus results in not only distinct solvatochromic PL but also distinct thermochromic PL. In addition, they all show typical self-trapped exciton triplet emissions. The additional supramolecular interactions from guest molecules can enhance the photoluminescence quantum yield to be as high as 95%.

Crystalline-Phase-Recognition-Induced Domino Phase Transition and Luminescence Switching for Advanced Information Encryption

Herein, a new mechanism, namely, crystalline phase recognition (CPR), is proposed for the single-crystal-to-single-crystal (SCSC) transition of metal halides. Chiral β-[Bmmim]₂ SbCl₅ (Bmmim=1-butyl-2,3-methylimidazolium) can recognize achiral α-[Bmmim]₂ SbCl₅ on the basis of a key-lock feature through intercontact of their single crystals, resulting in a domino phase transition (DPT). The concomitant photoluminescence (PL) switching enables observation of the DPT in situ. The liquid eutectic interface, stress-strain transfer, and feasible thermodynamics are key issues for the CPR. DFT calculations and PL measurements revealed that the optical absorption and emission of the isomers mainly originate from [SbCl₅ ]^2- anions. The structural effects (e.g., supramolecular interactions and [SbCl₅ ]^2- distortion) on the optical emission are clarified. As a novel type of stimuli response, the CPR-induced DPT and luminescence switching exhibit potential for application in advanced time-resolved information encryption.