The Structures of s2Metal Complexes in the Ground and sp Excited States

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.

Full-color, time-valve controllable and Janus-type long-persistent luminescence from all-inorganic halide perovskites

Long persistent luminescence (LPL) has gained considerable attention for the applications in decoration, emergency signage, information encryption and biomedicine. However, recently developed LPL materials - encompassing inorganics, organics and inorganic-organic hybrids - often display monochromatic afterglow with limited functionality. Furthermore, triplet exciton-based phosphors are prone to thermal quenching, significantly restricting their high emission efficiency. Here, we show a straightforward wet-chemistry approach for fabricating multimode LPL materials by introducing both anion (Br-) and cation (Sn2+) doping into hexagonal CsCdCl3 all-inorganic perovskites. This process involves establishing new trapping centers from [CdCl6-nBrn]4- and/or [Sn2-nCdnCl9]5- linker units, disrupting the local symmetry in the host framework. These halide perovskites demonstrate afterglow duration time ( > 2,000 s), nearly full-color coverage, high photoluminescence quantum yield ( ~ 84.47%), and the anti-thermal quenching temperature up to 377 K. Particularly, CsCdCl3:x%Br display temperature-dependent LPL and time-valve controllable time-dependent luminescence, while CsCdCl3:x%Sn exhibit forward and reverse excitation-dependent Janus-type luminescence. Combining both experimental and computational studies, this finding not only introduces a local-symmetry breaking strategy for simultaneously enhancing afterglow lifetime and efficiency, but also provides new insights into the multimode LPL materials with dynamic tunability for applications in luminescence, photonics, high-security anti-counterfeiting and information storage.

White light emission in 0D halide perovskite [(CH3)3S]2SnCl6·H2O crystals through variation of doping ns2 ions

With the rapid development of white LEDs, the research of new and efficient white light emitting materials has attracted increasing attention. Zero dimensional (0D) organic-inorganic hybrid metal halide perovskites with superior luminescent property are promising candidates for LED application, due to their abundant and tailorable structure. Herein, [(CH3)3S]2SnCl6·H2O is synthesized as a host for dopant ions Bi3+ and Sb3+. The Sb3+ doped, or Bi3+/Sb3+ co-doped, [(CH3)3S]2SnCl6·H2O has a tunable optical emission spectrum by means of varying dopant ratio and excitation wavelength. As a result, we can achieve single-phase materials suitable for emission ranging from cold white light to warm white light. The intrinsic mechanism is examined in this work, to clarify the dopant effect on the optical properties. The high stability of title crystalline material, against water, oxygen and heat, makes it promising for further application.

Multi-Mode Photoluminescence Regulation in a Zero-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite─[(CH3)4N]2SnCl6

Metal ion-doped zero-dimensional halide perovskites provide good platforms to generate broadband emission and explore the fundamental dynamics of emission regulations. Recently, Sb3+-doped zero-dimensional halide perovskites have attracted considerable attention for the high quantum yield of yellow emission; however, the triplet state recombination is activated and the singlet state emission is usually absent. Herein, we fabricate an Sb3+-doped zero-dimensional [(CH3)4N]2SnCl6 perovskite that can induce singlet and triplet emission. Density functional theory calculation shows that there are some overlaps between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals, which may induce a large energy separation between the lowest excited triplet states (T1) and the lowest excited singlet states (S1) [ΔE(S1 - T1)], impeding all the carriers' transfer from the singlet state to the triplet state. As a result, the reserved singlet emission together with the triplet emission can be regulated by excitation wavelength in situ. In addition, different Bi3+ ratios are co-doped into Sb3+@[(CH3)4N]2SnCl6, resulting in a photoluminescence ex situ regulation. Single-phase white light LED and optical anti-counterfeiting are developed further.

Second harmonic generation from symmetry breaking stimulated by mixed organic cations in zero-dimensional hybrid metal halides

Mixing cations with different chemical properties to induce the generation of asymmetric structures is a new approach for tuning the optical properties of hybrid organic-inorganic metal halides (HOIMHs). In this study, zero-dimensional (C₉N₃H₁₅)(C₉H₁₃SO)MBr₆ (M = Bi/Sb, [C₉N₃H₁₅]²⁺ = [(C₄N₂H₁₀)(C₅NH₅)]²⁺ and [C₉H₁₄SO]⁺ = [CH₃(C₆H₄)OS(CH₃)₂]⁺) are synthesized. Two different cations cause both compounds to crystallize in the polar space group P2₁2₁2₁, thus resulting in significant phase matchable second harmonic generation under a 1064 nm laser excitation. Thus, (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit intensities that are approximately 1.8 and 1.7 times that of KH₂PO₄, respectively. The results of density functional theory calculations show that both (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit direct bandgaps of 2.95 and 2.81 eV, respectively. Additionally, because of the distortion of the inorganic octahedra, (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibited bright yellow emission at room temperature, which is attributed to ns² fluorescence emission. We believe that the symmetry of the HOIMH crystal structure can be broken by introducing spatially differentiated bifunctional organic cations, which consequently enables even-order nonlinear activities.

Supramolecular Assembly of Halide Perovskite Building Blocks

The structural diversity and tunable optoelectronic properties of halide perovskites originate from the rich chemistry of the metal halide ionic octahedron [MX₆]^n- (M = Pb²⁺, Sb³⁺, Te⁴⁺, Sn⁴⁺, Pt⁴⁺, etc.; X = Cl^-, Br^-, and I^-). The properties of the extended perovskite solids are dictated by the assembly, connectivity, and interaction of these octahedra within the lattice environment. Hence, the ability to manipulate and control the assembly of the octahedral building blocks is paramount for constructing new perovskite materials. Here, we propose a systematic supramolecular strategy for the assembly of [MX₆]^n- octahedra into a solid extended network. Interaction of alkali metal-bound crown ethers with the [M(IV)X₆]^2- octahedron resulted in a structurally and optoelectronically tunable "dumbbell" structural unit in solution. Single crystals with diverse packing geometries and symmetries will form as the solid assembly of this new supramolecular building block. This supramolecular assembly route introduces a new general strategy for designing halide perovskite structures with potentially new optoelectronic properties.

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.

Ultrafast Solution-Phase Photophysical and Photochemical Dynamics of Hexaiodobismuthate(III), the Heart of Bismuth Halide Perovskite Solar Cells

The ultrafast relaxation pathways in a hexaiodide bismuth(III) complex, BiI₆^3-, excited at 530 nm in acetonitrile solution are studied by means of femtosecond transient absorption spectroscopy supported by steady-state absorption/emission measurements and DFT computations. Radiationless relaxation out of the Franck-Condon, largely metal-centered (MC) triply degenerate ³T_1u state (46 ± 19 fs), is driven by vibronic coupling due to the Jahn-Teller effect in the excited state. The relaxation populates two lower-energy states: a ligand-to-metal charge transfer (LMCT) excited state of ³π I(5p_π) → Bi(6p) nature and a luminescent "trap" ³A_1u(³P₀) MC state. Coherent population transfer from the initial ³T_1u into the ³π LMCT state occurs in an oscillatory, stepwise manner at ∼190 and ∼550 fs with a population ratio of ∼4:1. The ³π LMCT state decays with a 2.9 ps lifetime, yielding two short-lived reaction intermediates of which the first one reforms the parent ground state with a 15 ps time constant, and the second one decays on a ∼5 ps timescale generating the triplet product species, which persists to the longest 2 ns delay times investigated. This product is identified as the η² metal-ligated diiodide-bismuth adduct with the intramolecularly formed I-I bond, [(η²-I₂)Bi(II)I₄]^3-, which is the species of interest for solar energy conversion and storage applications. The lifetime of the "trap" ³A_1u state is estimated to be 13 ns from the photoluminescence quenching of BiI₆^3-. The findings give insight into the excited-state relaxation dynamics and the photochemical reaction mechanisms in halide complexes of heavy ns² metal ions.

Component Engineering to Tailor the Structure and Optical Properties of Sb-Doped Indium-Based Halides

Controlling the structure of halide perovskites through component engineering, and thus revealing the changes in luminescence properties caused by the conversion of crystal structure, is of great significance. Herein, we report a controllable synthetic strategy of three-dimensional (3D) Cs₂KInCl₆ and zero-dimensional (0D) (Cs/K)₂InCl₅(H₂O) halide perovskites by changing the Cs/K feed ratio. 3D Cs₂KInCl₆ double perovskites are obtained at the Cs/K feed ratio of 1:1, while 0D (Cs/K)₂InCl₅(H₂O) perovskites are formed at the Cs/K feed ratio of 2:1. Further, a reversible crystal structure transformation between 3D Cs₂KInCl₆ double perovskites and 0D (Cs/K)₂InCl₅(H₂O) perovskites can be achieved by subsequent addition of metal-salt precursors. In addition, the emission efficiency of two perovskite structures can be greatly boosted by breaking the forbidden transition through Sb doping, and as a result, a novel green/yellow reversible emission switch is generated. Meanwhile, the relationship between perovskite structure and luminescence mechanism has been systematically revealed. These environmentally stable halide perovskites have great potential to be applied in optoelectronic devices.

Zero-Dimensional Lead-Free Halide with Indirect Optical Gap and Enhanced Photoluminescence by Sb Doping

Three new lead-free organic-inorganic metal halides (OIMHs) (C₇H₈N₃)₃InX₆·H₂O (X = Cl, Br) and (C₇H₈N₃)₂SbBr₅ were synthesized. First-principles calculations indicate that the highest occupied molecular orbitals (HOMOs) of the two In-based OIMHs are constituted of π orbitals from [C₇H₈N₃]⁺ spacers. (C₇H₈N₃)₃InX₆·H₂O (X = Cl, Br) shows an indirect optical gap, which may result from this organic-contributed band edge. Despite the indirect-gap nature with extra phonon process during absorption, the photoluminescence of (C₇H₈N₃)₃InBr₆·H₂O can still be significantly enhanced through Sb doping, with the internal photoluminescence quantum yields (PLQY) increased 10-fold from 5% to 52%. A white light-emitting diode (WLED) was fabricated based on (C₇H₈N₃)₃InBr₆·H₂O:Sb³⁺, exhibiting a high color-rendering index of 90. Our work provides new systems to deeply understand the principles for organic spacer choice to obtain the 0D metal OIMHs with specific band structure and also the significant enhancement of luminescence performance by chemical doping.

Thallium-based heavy inorganic scintillators: recent developments and future perspectives

The current development status and future perspectives of Tl-based inorganic scintillators are highlighted in this study.

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%.

Light-Emitting 0D Hybrid Metal Halide (C3H12N2)2Sb2Cl10 with Antimony Dimers

Low-dimensional organic-inorganic metal halides (OIMHs), as emerging light-emitting materials, have aroused widespread attention owing to their unique structural tunability and photoelectric characteristics. OIMHs are also promising materials for optoelectronic equipment, light-emitting diodes, and photodetectors. In this study, (C₃H₁₂N₂)₂Sb₂Cl₁₀ (C₃H₁₂N₂²⁺ is an N-methylethylenediamine cation), a new zero-dimensional OIMH, has been reported, and (C₃H₁₂N₂)₂Sb₂Cl₁₀ possesses a P2₁/n space group. The (C₃H₁₂N₂)₂Sb₂Cl₁₀ structure contains [Sb₂Cl₁₀]^4- dimers (composed of two edge-sharing [SbCl₆]^3- octahedra) that are surrounded by C₃H₁₂N₂²⁺ cations. The experimental band gap of (C₃H₁₂N₂)₂Sb₂Cl₁₀ is 3.80 eV, and density functional theory calculation demonstrates that (C₃H₁₂N₂)₂Sb₂Cl₁₀ possesses a direct band gap, with the edge of the band gap mainly contributed from the inorganic units. (C₃H₁₂N₂)₂Sb₂Cl₁₀ exhibits good ambient and thermal stability. Under 395 nm excitation at room temperature, (C₃H₁₂N₂)₂Sb₂Cl₁₀ exhibits a broad emission with a full width at half-maximum of ∼114 nm, peaking at 480 nm, and the broad emission was ascribed to self-trapped exciton emission.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials

Seven novel bismuth(III)-halide phases, Bi₂Cl₆(terpy)₂·0.5(H₂O) (1), Bi₂Cl₄(terpy)₂(k₂-TC)₂(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k₂-TC)₂ (3A-Cl), BiBr(terpy)(k₂-TC)₂ (3A-Br), BiCl(terpy)(k₂-TC)₂ (3B-Cl), [BiCl(terpy)(k₂-TC)₂][Bi(terpy)(k₂-TC)₃]·0.55(TCA) (4), [BiBr₃(terpy)(MeOH)] (5), and [BiBr₂(terpy)(k₂-TC)][BiBr_1.16(terpy)(k₂-TC)_1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX₃ (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi_1-xEu_xCl, with the general formula Bi_1-xEu_xCl(terpy)(k₂-TC)₂ (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.

Role of Polyhedron Unit in Distinct Photophysics of Zero-Dimensional Organic-Inorganic Hybrid Tin Halide Compounds

The zero-dimensional (0D) metal halides comprising isolated metal-halide polyhedra are the smallest inorganic quantum systems and accommodate quasi-localized Frenkel excitons with unique photophysics of broadband luminescence, huge Stokes shift, and long lifetime. Little is known about the role of polyhedron type in the characteristics of 0D metal halides. We comparatively study three novel kinds of 0D hybrid tin halides having identical organic groups. They are efficient light emitters with a maximal quantum yield of 92.3%. Their most stable phases are composed of octahedra for the bromide and iodide but disphenoids for the chloride. They separately exhibit biexponential and monoexponential luminescence decays due to different symmetries and electronic structures. The chloride has the largest absorption and smallest emission photon energies. A proposed model regarding unoccupied-energy-band degeneracy explains well the experimental phenomena and reveals the crucial role of polyhedron type in determining optical properties of the 0D tin halides.

Efficiency-Tunable Single-Component White-Light Emission Realized in Hybrid Halides Through Metal Co-Occupation

Organic-inorganic hybrid metal halides have attracted widespread attention as emerging optoelectronic materials, especially in solid-state lighting, where they can be used as single-component white-light phosphors for white light-emitting diodes. Herein, we have successfully synthesized a zero-dimensional (0D) organic-inorganic hybrid mixed-metal halide (Bmpip)2PbxSn1-xBr4 (0 < x < 1, Bmpip+ = 1-butyl-1-methyl-piperidinium, C10H22N+) that crystallizes in a monoclinic system in the C2/c space group. Pb2+ and Sn2+ form a four-coordinate seesaw structure separated by organic cations forming a 0D structure. For different excitation wavelengths, (Bmpip)2PbxSn1-xBr4 (0 < x < 1) exhibits double-peaked emission at 470 and 670 nm. The emission color of (Bmpip)2PbxSn1-xBr4 can be easily tuned from orange-red to blue by adjusting the Pb/Sn molar ratio or excitation wavelength. Representatively, (Bmpip)2Pb0.16Sn0.84Br4 exhibits approximately white-light emission with high photoluminescence quantum yield up to 39%. Interestingly, the color of (Bmpip)2PbxSn1-xBr4 can also be easily tuned by temperature, promising its potential for application in temperature measurement and indication. Phosphor-converted light-emitting diodes are fabricated by combining (Bmpip)2PbxSn1-xBr4 and 365 nm near-UV LED chips and exhibit high-quality light output.

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.

Realizing Tunable White Light Emission in Lead-Free Indium(III) Bromine Hybrid Single Crystals through Antimony(III) Cation Doping

Low-dimensional metal halide hybrids (OIMHs) have recently been explored as single-component white-light emitters for use in solid-state lighting. However, it still remains challenging to realize tunable white-light emission in lead-free zero-dimensional (0D) hybrid system. Here, a combination strategy has been proposed through doping Sb³⁺ enabling and balancing multiple emission centers toward the multiband warm white light. We first synthesized a new lead-free 0D (C₈NH₁₂)₆InBr₉·H₂O single crystal, in which isolated [InBr₆]^3- octahedral units are separated by large organic cations [C₈NH₁₂]⁺. (C₈NH₁₂)₆InBr₉·H₂O exhibits dual-band emissions with one intense cyan emission and a weak red emission tail. The low-energy ultrabroadband red emission tail can be greatly enhanced by the Sb³⁺ doping. Experimental data and first-principles calculations reveal that the original dominant cyan emission is originated from the organic cations [C₈NH₁₂]⁺ and that the broadband red emission is ascribed to self-trapped excitons in [In(Sb)Br₆]^3-. When the Sb concentration is 0.1%, a single-component warm white-light emission with a photoluminescence quantum efficiency of 23.36%, correlated color temperature of 3347 K, and a color rendering index up to 84 can be achieved. This work represents a significant step toward the realization of single-component white-light emissions in environmental-friendly, high-performance 0D metal halide light-emitting materials.

Building Blocks of Hybrid Perovskites: A Photoluminescence Study of Lead-Iodide Solution Species

In this work, we present a detailed investigation of the optical properties of hybrid perovskite building blocks, [PbI2+n ]n- , that form in solutions of CH3 NH3 PbI3 and PbI2 . The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH3 NH3 PbI3 and PbI2 solutions were measured in various solvents and a broad concentration range. Both CH3 NH3 PbI3 and PbI2 solutions exhibit absorption features attributed to [PbI3 ]1- and [PbI4 ]2- complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI2 . For the first time, we show that the [PbI2+n ]n- species in both solutions of CH3 NH3 PbI3 and PbI2 exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH3 NH3 PbI3 and PbI2 solutions are dominated by coordination complexes between Pb2+ and I- . Finally, the impact of these complexes on the properties of solid-state perovskite semiconductors is discussed in terms of defect formation and defect tolerance.

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.

Crystal structure, vibrational spectroscopy and optical properties of a one-dimensional organic-inorganic hybrid perovskite of [NH3CH2CH(NH3)CH2]BiCl5

In this work the crystal structure by single crystal X-ray measurement and optical properties of 1D propane-1,2-diammonium pentachlorobismuthate [NH₃CH₂CH(NH₃)CH₃]BiCl₅ organic-inorganic hybrid perovskite are presented. It is prepared by mixing ethanolic solution of equimolar ratios (1:1) of its basic components. The title compound crystallized in the noncentrosymmetric orthorhombic space group Pca2₁ with Z = 8 molecules per unit cell. The unit-cell parameters are a = 19.8403 (7) Å, b = 6.3303 (2) Å, c = 19.0314 (7) Å. The vibrational spectra are studied by Raman and infrared spectroscopy. The optical properties show a strong absorption in the ultraviolet region, the band gap energy E_g is found to be 3.15 eV. Cathodoluminescence measurements are also discussed.

Synthesis of a New Chloro Antimony Complex with Pyridinium Derivative: Crystal Structure, Hirshfeld Surface Analysis, Vibrational, and Optical Properties

The new organic–inorganic hybrid material (C6H7N2S)2[SbCl4]Cl was synthesized by slow evaporation method and characterized by single-crystal X-ray diffraction, infrared absorption, Hirshfeld surface analysis, optical absorption and photoluminescence measurements. The Centro symmetric compound crystallizes in the triclinic system of space group $${\text{P}}\bar{1}$$P1¯ with two formula units cell (Z = 2).The crystal structure is composed of a discrete [SbCl4]− anion and two isolated chloride Cl− anions which carried the same negative charge to balance the total charge of this compound surrounded by the 4 pyridiniumethioamide cations. Organic and inorganic parts which are linked by means of hydrogen bonding contacts N–H···Cl with N···Cl length are varied in the range of 3.221–3.456 Å to form a Zero-dimensional network. The infrared study performed at room temperature charge in the 4000–400 cm−1 frequency regions confirms the existence of the organic cation [C6H7N2S]+ and that of the [SbCl4]− anion. The Photoluminescence spectrum exhibits a broad and strong band of luminescence located at 1.95 eV (635 nm), which can be even observed with the naked eye at room temperature and is due to exaction emission. The various intermolecular interactions of the two independent cations and six chloride atoms were examined via Hirshfeld surface analysis.

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).

Halide Photoredox Chemistry

Halide photoredox chemistry is of both practical and fundamental interest. Practical applications have largely focused on solar energy conversion with hydrogen gas, through HX splitting, and electrical power generation, in regenerative photoelectrochemical and photovoltaic cells. On a more fundamental level, halide photoredox chemistry provides a unique means to generate and characterize one electron transfer chemistry that is intimately coupled with X-X bond-breaking and -forming reactivity. This review aims to deliver a background on the solution chemistry of I, Br, and Cl that enables readers to understand and utilize the most recent advances in halide photoredox chemistry research. These include reactions initiated through outer-sphere, halide-to-metal, and metal-to-ligand charge-transfer excited states. Kosower's salt, 1-methylpyridinium iodide, provides an early outer-sphere charge-transfer excited state that reports on solvent polarity. A plethora of new inner-sphere complexes based on transition and main group metal halide complexes that show promise for HX splitting are described. Long-lived charge-transfer excited states that undergo redox reactions with one or more halogen species are detailed. The review concludes with some key goals for future research that promise to direct the field of halide photoredox chemistry to even greater heights.

Ferroelectricity in bis(ethylammonium) pentachlorobismuthate(iii): synthesis, structure, polar and spectroscopic properties

A brief description of the thermal, structural and dielectric properties of bis(ethylammonium) pentachlorobismuthate(iii) ferroelectric with P_s that equals to 1.4 μC cm⁻² at 180 K is presented.

New Quasi-One-Dimensional Organic-Inorganic Hybrid Material: 1,3-Bis(4-piperidinium)propane Pentachlorobismuthate(III) Synthesis, Crystal Structure, and Spectroscopic Studies

The organic-inorganic hybrid compound (C13H28N2) BiCl5 was synthesized by solvothermal method. The crystal structure was solved by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic system space group Cmc21 with a=15.826(4) Å, b=18.746(6) Å, c=7.470(3) Å, and Z=4. The crystal structure was refined down to R=0.019. It consists of corrugated layers of [BiCl5]2− chains, separated by organic [H2TMDP]2+ cations (TMDP=1,3-Bis(4-piperidyl)propane = C13H26N2). The crystal cohesion is achieved by hydrogen bonds N–H⋯Cl joining the organic and inorganic layers. The influence of the organic cations' flexibility is discussed. Raman and infrared spectra of the title compound were recorded in the range of 50–400 and 400–4000 cm−1, respectively. Semiempirical parameter model three (PM3) method has been performed to derive the calculated IR spectrum. The crystal shape morphology was simulated using the Bravais-Friedel and Donnay-Harker model.

Lead as its own luminescent sensor

Lead (II) in polar organic solvents such as acetone, acetonitrile, and propylenecarbonate with excess bromide generates the highly luminescent lead-halide cluster Pb(4)Br(11)(3)(-). This in situ sensor does not rely on a host-guest relationship and, thus, is intrinsically selective and sensitive, allowing for the detection of lead at nanomolar concentrations. The cluster's emission maximum and relaxation kinetics are temperature dependent and indicate a close spacing of intralead and intracluster electronic energy levels.