Dopant effect on the optical and thermal properties of the 2D organic-inorganic hybrid perovskite (HDA)2PbBr4.

Lead-based two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) are popular materials with various optical properties, which can be tuned through metal ion doping. Due to the size and valence misfit, metal ion dopants in 2D lead-based HOIPs are still limited. In this work, Mn2+, Sb3+ and Bi3+ are doped into 2D (HDA)2PbBr4 (HDA = protonated dopamine) successfully. As a result, the dopants in 2D (HDA)2PbBr4 can induce their characteristic optical spectra, which is studied at different temperatures and excitation powers. The temperature-dependent energy transfer in the Mn-doped sample has been clarified, in which abnormal phenomena including negative thermal quenching have been observed. In addition, the dopant ions can impact the phase transition temperatures of the samples, especially lowering their crystallization temperatures greatly. The mussel-inspired organic cation, feasible metal ion regulation, and superior stability provide (HDA)2PbBr4 potential for further applications.

Supramolecular-Interactions-Modulated Photoluminescence in Indium Bromide-Based Isomers.

Here, two isomeric ionic zero-dimensional indium bromide crystals of α (1)/ß (2)-[OPy][InBr4(Phen)] (OPy = N-octylpyridinium; Phen = 1,10-phenanthroline) have been isolated simply by changing the cooling conditions in solvothermal syntheses. Structural comparisons indicate their different supramolecular interactions, which can be confirmed by Hirshfeld surface analyses. The crystal 2 has additional hydrogen bonds and π-π interactions; as a result, the more compact stacking of 2 could result in a 10-fold higher photoluminescence (PL) quantum yield (PLQY) than that of 1. Density functional theory calculations confirm the electron transition from the inorganic moiety to the organic ligand, which provides a further understanding of the optical process. This work provides a new idea for designing PL indium-based halides by understanding the structure-PL relationship.

A High-Rigidity Organic-Inorganic Metal Halide Hybrid Enabling Reversible and Enhanced Self-Trapped Exciton Emission under High Pressure.

Zero-dimensional organic-inorganic metal halide hybrids provide ideal bulk-crystal platforms for exploring the pressure engineering of electron-phonon coupling (EPC) and self-trapped exciton (STE) emission at the molecular level. However, the low stiffness of inorganic clusters hinders the reversible tuning of these physical properties. Herein, we designed a Sb3+-doped metal halide with a high emission yield (89.4%) and high bulk modulus (35 GPa) that enables reversible and enhanced STE emission (20-fold) under pressure. The high lattice rigidity originates from the corner-shared cage-structured inorganic tetramers and ring-shaped organic ligands. Further, we reveal that the pressure-enhanced emission regime below 4.5 GPa is owing to the lattice hardening and preferably EPC strength reducing, while the pressure-insensitive emission regime within 4.5-8.5 GPa results from the enhanced intercluster Coulombic attraction force that resists intracluster compression. These results provide insights into the structure-property relation and molecular engineering of zero-dimensional metal halides toward wide-band and pressure-sensitive light sources.

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.

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.

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.

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.

The moisture-responsive structural transformation of manganochlorine for water-soluble luminescent switching ink.

CsMnCl3(H2O)2 (CMCH) has been widely investigated for magnetic and optical applications, including anti-Stokes photoluminescence, microwave absorption, and magnon-assisted optical transitions. Herein, CMCH crystals, which are colorless and transparent (unlike the pink crystals reported previously), were obtained through a unique approach. Consequently, a high-resolution optical absorption spectrum and distinct thermal behavior were observed. The reversible (de)hydration of CMCH being accompanied by photoluminescence switching (mainly in terms of the color temperature) was rationalized using crystal structure analysis. As a result, water-soluble CMCH could be applied as a moisture-responsive luminescent ink. Moreover, density functional theory (DFT) calculations were performed to understand the optical absorption of CMCH.

Modulation of the Structure and Photoluminescence of Bismuth(III) Chloride Hybrids by Altering the Ionic-Liquid Cations.

Two bismuth(III) halides hybrids with room-temperature phosphorescence (RTP), namely, [BPy]2[Bi2Cl8(bpym)] (1, BPy = N-butylpyridinium) and [EPy]2[Bi2Cl8(bpym)] (2, EPy = N-ethylpyridinium), were synthesized and characterized. Structural comparison reveals that 1 and 2 possess similar anionic zigzaglike chain of [Bi2Cl8(bpym)]n2n-; however, different packing modes of anion/cations and thus different weak interactions. Interestingly, the utilization of pyridinium cations with different length of alkyl chain could tune the RTP behaviors efficiently. The RTP quantum yield (QY) is increased more than 5-fold from 1 to 2 probably due to more rigid structure of 2 arising from the additional H-bond and anion-π interactions, as confirmed by Hirshfeld surfaces analyses and PLATON calculations. Moreover, additional π-π interactions in 1 could stabilize the triplet excitons, leading to an average lifetime of 1 (11.36 ms at 77 K and 1.407 ms at 298 K) being higher than 2 (0.3618 ms at 77 K and 0.07511 ms at 298 K). Density functional theory (DFT) calculations confirm that inorganic moiety to organic ligand charge-transfer (IOCT) is involved in the phosphorescence process. The present work provides a new sight into the design of RTP metal halides through studying the structure-RTP relationship.

Autologous Cobalt Phosphates with Modulated Coordination Sites for Electrocatalytic Water Oxidation.

The correlation between metal coordination and electrocatalytic water oxidation performance is elusive in many cobalt-based materials. Herein, we designed an ideal Co phosphate-based platform to explore the effect of coordination environment on oxygen evolution reaction (OER) activity. The cobalt geometry was modulated from octahedral to tetrahedral by simple removal of water ligands in Co3 (PO4 )2 ⋅8 H2 O. Other features except the coordination structure in the two autologous materials remain similar. The two analogues display the same OER kinetics, but the anhydrous Co3 (PO4 )2 exhibits a greatly enhanced OER activity. On the basis of Raman and operando XAS results, the higher intrinsic activity of the Co tetrahedral sites is because they facilitate the formation of active high valent cobalt (hydr)oxide intermediates during OER. This work not only brings insights of OER on Co-based electrocatalysts but also provides a reference system to study the effect of metal geometry on electrocatalysis.

Material Design and Optoelectronic Properties of Three-Dimensional Quadruple Perovskite Halides.

The discovery of new halide perovskite-type structures could favor the exploration of optoelectronic materials, as in the case of double perovskites applied in solar cells, light-emitting diodes, and X-ray detectors. In this work, we propose a strategy for designing quadruple perovskites by heterovalent cation transmutation from double perovskites. Two stable quadruple perovskite halides, i.e., Cs4CdSb2Cl12 and Cs4CdBi2Cl12, with a vacancy-ordered three-dimensional (3D) crystal structure were predicted through symmetry analysis and density functional theory (DFT) calculations. The title perovskite halides are also electronically 3D with direct forbidden bandgaps. Following the indication provided by the DFT results, Cs4CdSb2Cl12 and Cs4CdBi2Cl12 as unique quadruple perovskites were successfully synthesized by a solvothermal method. The steady-state photoluminescence (PL) shows wide emission, while the transient PL exhibits carrier recombination lifetime on the order of microseconds at low temperature. The quadruple perovskite halides provide an alternative platform for promising optoelectronic material design in addition to simple and double perovskites.