Fluorescence Emission Is Highly Structure-Dependent in Hybrid Lead Halides

Hybrid lead halide perovskites have received extensive scientific attention owing to their great potential in the field of fluorescent displays and light-emitting diodes. Currently, most luminescent materials contain functional molecular and rare-earth metal ion parts. However, the mechanism of photoluminescence property in two-dimensional hybrid lead halide perovskites with different layered inorganic skeletons has been reported rarely. To better understand the effect of an inorganic skeleton on the fluorescence property, here, we report three organic-inorganic hybrid materials with different layered inorganic frameworks: (MACH)₂·PbBr₄ (Prv-1, MACH = cyclohexylmethylammonium), (2-MPQ)·PbBr₄ (Prv-2, 2-MPQ = 2-methylpiperazinium), and (TMBA)₄·Pb₃Br₁₀ (Prv-3, TMBA = N'N'N'-trimethylbenzylammonium). Among them, Prv-1 is a (100)-oriented perovskite, Prv-2 belongs to the (110)-oriented perovskite, and the inorganic framework of Prv-3 possesses [Pb₃Br₁₀] units. Interestingly, Prv-1 has a strong blue-violet fluorescence emission, while the luminescence effect of Prv-2 is very weak; notably, Prv-3 emits a charming bright-orange light. Meanwhile, results of theoretical computational studies also reveal that the electronic structure of all three compounds is highly dependent on structurally distorted [PbBr₆] octahedra, and the frontier molecular orbital (FMO) analysis further suggests that HOMO and LUMO of Prv-3 are contributed by inorganic and organic components, respectively. In addition, all three materials belong to direct band gap semiconductors, and the band gaps are 2.79, 2.97, and 2.76 eV, respectively. Significantly, there are obvious differences in conduction bands. Based on the above analysis, the photoluminescence mechanism of three hybrid materials is explained from the electronic levels. Consequentially, this work might provide practical strategies and perspectives for exploring novel structure-related properties.

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

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

Temperature-Responsive Photoluminescence and Elastic Properties of 1D Lead Halide Perovskites R- and S-(Methylbenzylamine)PbBr3

Low-dimensional metal halide perovskites (MHPs) have received much attention due to their striking semiconducting properties tunable at a molecular level, which hold great potential in the development of next-generation optoelectronic devices. However, the insufficient understanding of their stimulus-responsiveness and elastic properties hinders future practical applications. Here, the thermally responsive emissions and elastic properties of one-dimensional lead halide perovskites R- and S-MBAPbBr3 (MBA+ = methylbenzylamine) were systematically investigated via temperature-dependent photoluminescence (PL) experiments and first-principles calculations. The PL peak positions of both perovskites were redshifted by about 20 nm, and the corresponding full width at half maximum was reduced by about 40 nm, from ambient temperature to about 150 K. This kind of temperature-responsive self-trapped exciton emission could be attributed to the synergistic effect of electron-phonon coupling and thermal expansion due to the alteration of hydrogen bonding. Moreover, the elastic properties of S-MBAPbBr3 were calculated using density functional theory, revealing that its Young's and shear moduli are in the range of 6.5-33.2 and 2.8-19.5 GPa, respectively, even smaller than those of two-dimensional MHPs. Our work demonstrates that the temperature-responsive emissions and low elastic moduli of these 1D MHPs could find use in flexible devices.

Investigation of Metastable Low Dimensional Halometallates

The solvothermal synthesis, structure determination and optical characterization of five new metastable halometallate compounds, [1,10-phenH][Pb3.5I8] (1), [1,10-phenH2][Pb5I12]·(H2O) (2), [1,10-phen][Pb2I4] (3), [1,10-phen]2[Pb5Br10] (4) and [1,10-phenH][SbI4]·(H2O) (5), are reported. The materials exhibit rich structural diversity and exhibit structural dimensionalities that include 1D chains, 2D sheets and 3D frameworks. The optical spectra of these materials are consistent with bandgaps ranging from 2.70 to 3.44 eV. We show that the optical behavior depends on the structural dimensionality of the reported materials, which are potential candidates for semiconductor applications.

Highly Efficient Broadband White-light Emission in Two-dimensional Semi-conductive Hybrid Lead–Chlorine Halide

White-light emission (WLE) materials based on organic-inorganic hybrid Lead halides have drawn considerable attentions, because of its applications in light-emission equipments. Despite considerable efforts, there is still a lack of...

A One-Dimensional Broadband Emissive Hybrid Lead Iodide with Face-Sharing PbI6 Octahedral Chains

One-dimensional (1D) organic-inorganic hybrid lead halides with unique core-shell quantum wire structures and splendid photoluminescence properties have been considered one of the most promising high-efficiency broadband emitters. However, studies on the broadband emissions in 1D purely face-shared lead iodide hybrids are still rare so far. Herein, we report on a new 1D lead iodide hybrid, (2cepyH)PbI₃ (2cepy = 1-(2-chloroethyl)pyrrolidine), characterized with face-sharing PbI₆ octahedral chains. Upon UV photoexcitation, this material shows broadband yellow emissions originating from the self-trapped excitons associated with distorted Pb-I lattices on account of the strong exciton-phonon coupling, as proved by variable-temperature emission spectra. Moreover, experimental and calculated results reveal that (2cepyH)PbI₃ is an indirect bandgap semiconductor, the band structures of which are governed by inorganic parts. Our work represents the first broadband emitter based on a 1D face-shared lead iodide hybrid and opens a new way to obtain the novel broadband emission materials.

Temperature-responsive emission and elastic properties of a new 2D lead halide perovskite

Two-dimensional (2D) organometallic halide perovskites (OHPs) are promising optoelectronic materials because of their excellent stability and tunable band gaps. Herein, we report the optical and elastic properties of a newly synthesized 2D lead halide perovskite, (C9H14ON)2PbI4 (C9H14ON+ = 4-methoxyphenethylammonium), by a combined experimental and theoretical approach. Our experiments demonstrate that (C9H14ON)2PbI4 shows a strong green emission under ambient conditions which is ascribed to its band gap of 2.4 eV. Moreover, our temperature-dependent photoluminescence (PL) experiments in the temperature range of 143-283 K reveal that the green emission red-shifts with increasing temperature, which is primarily attributed to the synergistic effect of thermal expansion and electron-phonon interactions. The elastic properties, obtained from density functional theory calculations, reveal that (C9H14ON)2PbI4 has relatively low modulus and anisotropy compared with other 2D materials.

Conjugated-Polypyridine-Derivative-Derived Semiconductive Iodoplumbates with Tunable Architectures and Efficient Visible-Light-Induced Photocatalytic Property

By mediation of the pH values, three novel inorganic-organic iodoplumbate hybrids, [Me₃TPT][Pb₃I₉] [1; Me₃TPT = trimethyl-2,4,6-tris(4-pyridyl)-1,3,5-triazine], [Me₃TPT]₂[Pb₉I₂₄] (2), and [Me₃TPT]₂[Pb₁₉I₄₄] (3), have been achieved under solvothermal conditions. The large conjugated in situ N-alkylation polypyridine derivatives act as structure-directing agents and electron acceptors, making the materials feature adjustable structural variations with 0D, 1D, and 2D structures and a potential semiconductive performance with narrow energy gaps (1.72, 1.80, and 1.78 eV for 1-3, respectively), which result in their efficient photocatalytic activity under visible-light irradiation. Theoretical calculation reveals that the conjugated organic moieties greatly contribute to the conduction band, leading to narrow band gaps. It is expected that the work will contribute to the exploitation of novel semiconducting halometallates by employing conjugated organic species as structure-directing agents.

Organic cations directed 1D [Pb3Br10]4− chains: syntheses, crystal structures, and photoluminescence properties

To diversify the luminescence properties of 1D perovskites, different organic amine cations were combined with 1D [Pb₃Br₁₀]⁴⁻ chains leading to a series of A₂Pb₃Br₁₀ homologues, displaying broadband near white-light emissions with highest CRI of 96.

(γ-Methoxy propyl amine)2PbBr4: a novel two-dimensional halide hybrid perovskite with efficient bluish white-light emission

A 2D hybrid perovskite based on alkoxyamine cations shows bright bluish white-light emission with a high PLQE of 6.85%.

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.

The red light emission in 2D (C4SH3CH2NH3)2SnI4 and (C4OH7CH2NH3)2SnI4 perovskites

Two-dimensional (2D) perovskites have a large exciton binding energy due to the structure of the quantum confinement, which produces a faster radiative recombination, and so are promising potential materials for light-emitting diodes. However, most of the highly efficient hybrid halide perovskites are based on the toxic Pb-based materials, so the replacement of Pb with less toxic and suitable substitute elements has been investigated for environmental efficient materials. Herein, we report the Sn-based 2D perovskites, which include (TPM)2SnI4 (TPM = C4SH3CH2NH3) and (TFF)2SnI4 (TFF = C4OH7CH2NH3), as red emission materials. Structural characterization by single crystal X-ray diffraction reveals that (TPM)2SnI4 undergoes a structural evolution from the orthorhombic space group Cmc21 (100 K) to Pbca (298 K), while the (TFF)2SnI4 perovskite exhibits the monoclinic space group P21/c at 100 K and 298 K. The inorganic framework of (TFF)2SnI4 was separated by the bilayer TFF chains with an empty space, which is an effective structure to increase the quantum confinement effect. The band gaps of the (TPM)2SnI4 (1.80 eV) and (TFF)2SnI4 (1.73 eV) compounds indicate the direct band gap semiconductor materials. From the time-resolved photoluminescence results, it can be seen that (TPM)2SnI4 produces uniform short emission (0.73 ns) throughout the entire powder crystals, whereas (TFF)2SnI4 has a uniform and long emission life time (47 ns). Temperature-dependent photoluminescence (PL) studies indicate that the (TPM)2SnI4 and (TFF)2SnI4 perovskites have a strong split red emission at low temperature due to the vibration of the inorganic framework. As the temperature increases, the PL spectra shift to the high energy region and the emission intensity decreases. The PL spectra of (TPM)2SnI4 and (TFF)2SnI4 perovskites have maximum peak wavelengths at 622 nm and 640 nm, and show the photoluminescence quantum yields of 0.30% and 1.71%, respectively.

Semiconducting crystalline inorganic-organic hybrid metal halide nanochains

One-dimensional (1D) inorganic-organic metal halide hybrids at the molecular level, which can be considered as arrays of nanochains isolated by organic components, have shown remarkable optical and electric properties. This review summarizes their reported structural types and shows how to modify their band gaps and optical and electric properties.

Non-transient thermo-/photochromism of iodobismuthate hybrids directed by solvated metal cations

Two iodobismuthate-based organic-inorganic hybrids, [M(DMSO)₈][Bi₂I₉] (M = La (1), Bi (2)), have been successfully designed and synthesized by using solvated metal cations as structure-directing agents (SDAs). 1 displays transient high-temperature thermochromism, which is similar to that of the characteristic low-temperature thermochromic properties of bulk bismuth iodide and iodobismuthate hybrids. In contrast, 2 exhibits distinguishing non-transient thermochromic properties stimulated by the different temperature ranges of the thermal treatments. More importantly, a comparison of the optical inertness of 1 and 2 also reveals novel photochromic behavior. The completely different thermo-/photo-responsive properties of 1 and 2 are mainly ascribed to the different binding abilities of the central metal cations with DMSO molecules, which cause a distinct transformation of the inorganic moiety and consequent modulation of band gaps.

Hybrid iodoplumbates with metal complexes: syntheses, crystal structures, band gaps and photoelectric properties

With the in situ-generated [Pb(MCP)₄]²⁺ (HMCP⁺ = 1-methyl-4-(carboxyl)pyridinium) or [M(phen)₃]²⁺ (M = Co, Fe and Ni; phen = 1,10-phenanthroline) complexes as structural directing agents and charge-balancing ions, we solvothermally synthesized and structurally characterized four new organic-inorganic hybrid iodoplumbates. Compound K₂[Pb(MCP)₄]Pb₃I₁₀ (1) represents the first K⁺ and [Pb(MCP)₄]²⁺ co-templated hybrid haloplumbate, and exhibits a curve-like anionic layer of [Pb₃I₁₀]_n^4n-. Compounds [M(phen)₃]Pb₂I₆·CH₃CN (M = Co (2), Fe (3) and Ni (4)) have isostructural phases, and feature a one-dimensional (1D) [Pb₂I₆]_n^2n- anionic chain characteristic of pyramid-like [PbI₅] units. The optical property studies show that compounds 1-4 exhibit semiconductor behaviors with the band gaps of 1.98-2.68 eV. In addition, the title compounds exhibited interesting photoelectrical responsive properties, with the photocurrent density in the order of 1 > 3 > 2 > 4. The thermal stabilities of the title compounds 1-4, as well as the theoretical band structure and density of states (DOS) of compounds 1 and 2 have also been studied.

[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.

Arranging strategies for A-site cations: impact on the stability and carrier migration of hybrid perovskite materials

An essential understanding is obtained from the cation engineering process into the expected excited-state properties of hybrid perovskite materials.

Achievement of intrinsic white light emission by hybridization-deformable haloplumbates with rigid luminescent naphthalene motifs

The combination of red emissions stemming from deformable haloplumbates and blue emissions originating from luminescent naphthalene motifs give rise to intrinsic single-component white-light emitters.

Photochromic and luminescent switchable iodoargentate hybrids directed by solvated lanthanide cations

A series of photochromic and luminescent switchable iodoargentate hybrids have been constructed by using solvated lanthanide cations as SDAs.

Broadband yellow light emitting performance based on zero-dimensional hybrid lead bromide trimers

Two new zero-dimensional organic–inorganic hybrid lead halides based on linear [Pb₃Br₁₂]⁶⁻ trimers display broadband yellow light emissions with high photoluminescence quantum yields, exhibiting potential in the fabrications of white-light emitting diodes.