Reversible luminescent humidity chromism of organic-inorganic hybrid PEA2MnBr4 single crystals

Efficient Ultraviolet Circularly Polarized Luminescence in Zero-Dimensional Hybrid Cerium Bromides

Ultraviolet circularly polarized luminescence (UV-CPL) with high photon energy shows great potential in polarized light sources and stereoselective photopolymerization. However, developing luminescent materials with high UV-CPL performance remains challenging. Here, we report a pair of rare earth Ce3+-based zero-dimensional (0D) chiral hybrid metal halides (HMHs), R/S-(C14H24N2)2CeBr7, which exhibits characteristic UV emissions derived from the Ce 5d-4f transition. The compounds show simultaneously high photoluminescent quantum yields of (32-39)% and large luminescent dissymmetry factor (|glum|) values of (1.3-1.5)×10-2. Thus, the figures of merits of R/S-(C14H24N2)2CeBr7 are calculated to be (4.5-5.8)×10-3, which are superior to the reported UV-CPL emissive materials. Additionally, nearly 91 % of their PL intensities at 300 K can be well preserved at 380 K (LED operating temperature) without phase transition or decomposition, demonstrating the excellent structural and optical thermal stabilities of R/S-(C14H24N2)2CeBr7. Based on these enantiomers, the fabricated UV-emitting CP-LEDs exhibit high polarization degrees of ±1.0 %. Notably, the UV-CPL generated from the devices can significantly trigger the enantioselective photopolymerization of diacetylene with remarkable stereoselectivity, and consequently yield polymerized products with the anisotropy factors of circular dichroism (gCD) up to ±3.9×10-2, outperforming other UV-CPL materials and demonstrating their great potential as UV-polarized light sources.

Manipulating Chiroptical Activities in 0D Chiral Hybrid Manganese Bromides by Solvent Molecular Engineering

0D hybrid metal halides (0D HMHs) with fully isolated inorganic units provide an ideal platform for studying the correlations between chiroptical activities and crystal structures at atomic levels. Here, through the incorporation of different solvent molecules, a series of 0D chiral manganese bromides (RR/SS-C20H28N2)3MnBr8·2X (X = C2H5OH, CH3OH, or H2O) are synthesized to elucidate their chiroptical properties. They show negligible circular dichroism signals of Mn absorptions due to C2v-symmetric [MnBr4]2- tetrahedra. However, they display distinct circularly polarized luminescence (CPL) signals with continuously increased luminescence asymmetry factors (glum) from 10-4 (X = C2H5OH) to 10-3 (X = H2O). The increased glum value is structurally revealed to originate from the enhancement of [MnBr4]2- tetrahedral bond-angle distortions, due to the presence of different solvent molecules. Furthermore, (RR/SS-C20H28N2)MnBr4·H2O enantiomers with larger bond-angle distortions of [MnBr4]2- tetrahedra are synthesized based on hydrobromic acid-induced structural transformation of (RR/SS-C20H28N2)3MnBr8·2H2O enantiomers. Therefore, such (RR/SS-C20H28N2)MnBr4·H2O enantiomers exhibit enhanced CPL signals with |glum| up to 1.23 × 10-2. This work provides unique insight into enhancing chiroptical activities in 0D HMH systems.

Fine-Tuning Optoelectronic Features in Organic-Inorganic Hybrid Metal Halides: A Focus on the Phenylbutanammonium Series

Extensive research has been dedicated to exploring the potential applications of organic-inorganic hybrid metal halides in optoelectronics. This study presents findings on three metal halides based on phenylbutanammonium (PBA). Specifically, (PBA)2MnBr4(H2O)2 and (PBA)2Sn(IV)Cl6 exhibit zero-dimensional structures with P21/c and Pnma space groups, respectively, while (PBA)2Sn(II)Br4 features a two-dimensional structure with P1̅ space group. Under UV excitation, (PBA)2MnBr4(H2O)2 exhibits double emission arising from the 4T1 → 6A1 transitions of Mn2+ in two distinct coordination environments. The emission spectrum of (PBA)2SnCl6 aligns with that of PBACl, suggesting that the luminescence originates from the organic component. The yellow emission of (PBA)2SnBr4 is attributed to the self-trapped excitons. This study introduces the PBA series of compounds, revealing that varying metal ions and halogen combinations can adjust the structural dimensions and influence optical properties. The insights gained from this work serve as a guide for the preparation of efficient white light-emitting diodes.

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.

RGB tri-luminescence in organic-inorganic zirconium halide perovskites

Materials with two or more fluorescence features under different excitation sources have great potential in optical applications, but luminous materials with three emission characteristics have been largely undeveloped. Here, we report a novel zero-dimensional (0D) organic-inorganic hybrid ((C2H5)4N)2ZrCl6 perovskite with multiple emissions. The zirconium-based perovskite exhibits a red emission around 620 nm, a green emission at 527 nm, and a blue emission around 500 nm. The red and green emissions come from self-trapped excitons (STEs) and the d-d transitions of Zr(iv), respectively, which are caused by distortion of the [ZrCl6]2- octahedra. The blue emission is caused by thermally activated delayed fluorescence (TADF), which is similar to that of Cs2ZrCl6. The absolute photoluminescence quantum yield (PLQY) of the red and blue double emission is up to 83% and the PLQY of the green emission is 27%. With different combinations of ((C2H5)4N)2ZrCl6 samples, we achieve a variety of applications, including a two-color luminescent anti-counterfeiting device, a white light-emitting diode (WLED) with a color rendering index (CRI) of 95 and information encryption with different excitations. We also synthesize other hybrid zirconium perovskites with tri-luminescence through a similar method. Our work provides a potential set of excitation-dependent luminescent materials and is expected to expand the basic research and practical applications of multi-luminescence materials.

Designing Yolk-Shell Nanostructures for Reversible Water-Vapor-Responsive Dual-Mode Switching of Fluorescence and Structural Color

Metal halide perovskites offer ample opportunities to develop advanced optoelectronic devices. This work showcases that the integration of metal halide perovskites into metal oxide nanoshells with controllable interior cavities can enable water-vapor-responsive dual-mode switching of fluorescence and structural color. Through a ship-in-a-bottle method to introduce a controlled amount of CsPbBr3 into MnO2 nanoshells, we have designed CsPbBr3@MnO2 yolk-shell nanostructures, which can uptake a defined amount of water to exhibit rapid (less than 1 s) and reversible (≥100 cycles) responses in both fluorescence on-off and color change when exposed to dynamic water vapor. These responses originate from the water-triggered phase transformation of CsPbBr3 to CsPb2Br5 and the structural color change of the MnO2 shell. The altered electronic and bonding structure at the oxide-halide interface, rapid water accumulation in the yolk-shell cavity, and protective effect of the oxide shell facilitate the reversible transformations. The response characteristics of the yolk-shell nanostructures have been further demonstrated in fabricating patterned films capable of multiple fluorescence/structural color responses, highlighting their potential for applications in advanced anticounterfeiting and encryption.

Highly efficient and stable Cs3Mn0.93Zn0.07Br5@SiO2 for wide color gamut backlight displays

Mn-based perovskites have become a new candidate material for backlight display applications. However, low efficiency and poor stability are the key problems limiting the application of Mn-based perovskites. In this work, Zn-doped and SiO2-encapsulated Cs3MnBr5, denoted as Cs3Mn0.93Zn0.07Br5@SiO2 (CMZBS), was successfully synthesized to improve the photoluminescence quantum yield (PLQY) and stability. After Zn doping, the PLQY increased from 51% to 72% due to the reduction in the energy transfer between [MnBr4]2-. The PLQY can be further improved to 80% after coating SiO2. Compared with Cs3MnBr5 (CMB), CMZBS showed better stability against thermal, air, light, and polar solvents (ethanol and isopropanol). In addition, a white LED (WLED) device with a CIE of (0.323, 0.325) was fabricated by integrating CMZBS and the red phosphor K2SiF6:Mn4+ on a 465 nm blue GaN chip, which exhibited a high luminous efficiency of 92 lm W-1 and excellent stability, demonstrating its great potential application in wide color gamut displays.

Solid-State Synthesis and Optical Studies of Water-Stable Pb2+-Doped Mn2+ Complexes

The limited Mn2+ doping that occurs in lead halide perovskites has been widely described, while the Pb2+ doping that occurs in Mn2+ halide perovskites has not been studied well. Generally, a large amount of doping of Mn2+ in lead halide perovskite degrades the perovskite structure; eventually, high orange luminescence of Mn2+ dopant has not been achieved. In our present study, we followed a reverse strategy, i.e., Pb2+ doping in Mn2+ halide perovskites, to increase the amount of Mn2+ in halide perovskites through the high-energy ball milling method. This strategy yields bright-fluorescence orange light-emitting Mn2+-doped perovskite with a Mn/Pb ratio of 95%, which is the highest among Mn2+-doped perovskites. Zero-dimensional (0D) Mn2+ perovskites and two-dimensional (2D) Pb2+-doped Mn2+-based perovskites were successfully synthesized and characterized. During the mechanochemical engineering, Pb2+ ions partially occupy the site of Mn2+ ions and act as a luminescence activator. Mn2+-based 2D perovskites with the proper amounts of Pb2+ ions as dopant ions and phenylethylammonium (PEA+) as dielectric organic cations show enhanced stability in water. The dual-emissive properties of these 2D-Pb2+-doped Mn2+-based perovskites were also investigated by using single-particle imaging fluorescence. We believe that these findings will pave the way for designing eco-friendly dimension and bandgap tunable layered perovskites.

Water-Molecule-Induced Reversible Fluorescence in a One-Dimensional Mn-Based Hybrid Halide for Anticounterfeiting and Digital Encryption-Decryption

Hybrid metal halides with reversible transformation of structure and luminescence properties have attracted significant attention in anticounterfeiting. However, their long transition time and slow response rate may hinder the rapid identification of confidential information. Here, a one-dimensional hybrid manganese-based halide, i.e., (C5H11N3)MnCl2Br2·H2O, is prepared and demonstrates the phenomenon of water-molecule-induced reversible photoluminescence transformation. Heating for <40 s induces a dynamic transfer of red-emissive (C5H11N3)MnCl2Br2·H2O to green-emissive (C5H11N3)MnCl2Br2. In addition, the green emission can gradually revert to red emission during a cooling process in a moist environment, demonstrating excellent reversibility. It is found that the water molecule acts as an external stimulus to realize the reversible transition between red and green emission, which also exhibits remarkable stability during repeated cycles. Furthermore, with the assistance of heating and cooling, a complex digital encryption-decryption and an optical "AND" logical gate are achieved, facilitating the development of anticounterfeiting information security.

High-Temperature, Reversible, and Robust Thermochromic Fluorescence Based on Rb2 MnBr4 (H2 O)2 for Anti-Counterfeiting

Thermochromic fluorescent materials (TFMs) characterized by noticeable emission color variation with temperature have attracted pervasive attention for their frontier application in stimulus-response and optical encryption technologies. However, existing TFMs typically suffer from weak PL reversibility as well as limited mild operating temperature and severe temperature PL quenching. PL switching under extreme conditions such as high temperature will undoubtedly improve encryption security, while it is still challenging for present TFMs. In this work, high-temperature thermochromic fluorescence up to 473 K and robust structural and optical reversibility of 80 cycles are observed in Rb2 MnBr4 (H2 O)2 and related crystals, which is seldom reported for PL changes at such a high temperature. Temperature-driven nonluminous, red and green light emission states can be achieved at specific temperatures and the modulation mechanism is verified by in situ optical and structural measurements and single particle transition. By virtue of this unique feature, a multicolor anti-counterfeiting label based on a broad temperature gradient and multidimensional information encryption applications are demonstrated. This work opens a window for the design of inorganic materials with multi-PL change and the development of advanced encryption strategies with extreme stimuli source.

Strong Magnetically-Responsive Circularly Polarized Phosphorescence and X-Ray Scintillation in Ultrarobust Mn(II)-Organic Helical Chains

Over recent years, Mn(II)-organic materials showing circularly polarized luminescence (CPL) have attracted great interest because of their eco-friendliness, cheapness, and room temperature phosphorescence. Using the helicity design strategy, herein, chiral Mn(II)-organic helical polymers are constructed featuring long-lived circularly polarized phosphorescence with exceptionally high glum and ΦPL magnitudes of 0.021% and 89%, respectively, while remaining ultrarobust toward humidity, temperature, and X-rays. Equally important, it is disclosed for the first time that the magnetic field has a remarkably high negative effect on CPL for Mn(II) materials, suppressing the CPL signal by 4.2-times atB ⃗ $\vec{B}$  = 1.6 T. Using the designed materials, UV-pumped CPL light-emitting diodes are fabricated, demonstrating enhanced optical selectivity under right- and left-handed polarization conditions. On top of all this, the reported materials display bright triboluminescence and excellent X-ray scintillation activity with a perfectly linear X-ray dose rate response up to 174 µGyair  s-1 . Overall, these observations significantly contribute to the CPL phenomenon for multi-spin compounds and promote the design of highly efficient and stable Mn(II)-based CPL emitters.

Thermosalient effect of a naphthalene diimide and tetrachlorocobaltate hybrid and changes of color and magnetic properties by ammonia vapor

An organic-inorganic hybrid metal halide (OIMH), namely the electron-deficient naphthalene diimide (NDI) and [CoCl₄]^2- hybrid (1), showed potential as a sensor for ammonia and amines, in addition to magnetic changes upon vapochromism. Crystal 1 exhibited thermosalient behavior such as leaping and movement, at around 130 °C, which could be explained to be associated with the removal of water molecules from the crystal lattice as shown by TGA and DSC. Compound 1 changed from green to black within 5 minutes when exposed to ammonia vapor, which was attributed to the radical formation in the NDI moiety as evidenced by ESR, and this phenomenon was preserved even when other mono- and di-alkylamines were applied. The exposure of 1 to ammonia resulted in a subsequent color alteration, progressing from black to a gradually dark orange after one day (1_NH3_1 day). This transformation was concomitant with the formation of [Co(NH₃)₆]³⁺ from [CoCl₄]^2-, leading to a modification of the magnetic properties from paramagnetic Co(II) (S = 3/2) to diamagnetic Co(III) (S = 0). Based on these findings, compound 1 represents the first example of an OIMH that exhibits thermosalient behaviour, color change, and magnetic conversion upon exposure to ammonia.

Metal-Ion-Doped Manganese Halide Hybrids with Tunable Emission for Advanced Anti-Counterfeiting

Stimuli-responsive luminescent materials have received great attention for their potential application in anti-counterfeiting and information encryption. Manganese halide hybrids have been considered an efficient stimuli-responsive luminescent material due to their low price and adjustable photoluminescence (PL). However, the photoluminescence quantum yield (PLQY) of PEA₂MnBr₄ is relatively low. Herein, Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄ samples are synthesized, and show an intense green emission and orange emission, respectively. After doping with Zn²⁺, the PLQY of PEA₂MnBr₄ is elevated from 9% to 40%. We have found that green emitting Zn²⁺-doped PEA₂MnBr₄ could transform to a pink color after being exposed to air for several seconds and the reversible transformation from pink to green was achieved by using heating treatment. Benefiting from this property, an anti-counterfeiting label is fabricated, which exhibits excellent "pink-green-pink" cycle capability. Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ is acquired by cation exchange reaction, which shows intense orange emission with a high QY of 85%. The PL of Pb²⁺-doped PEA₂Mn_0.88Zn_0.12Br₄ decreases with increasing temperature. Hence, the encrypted multilayer composite film is fabricated relying on the different thermal responses of Zn²⁺- and Pb²⁺-doped PEA₂MnBr₄, whereby the encrypted information can be read out by thermal treatment.

Reversible Luminescent Switching Induced by Heat/Water Treatment in a Zero-Dimensional Hybrid Antimony(Ⅲ) Chloride

Recently zero-dimensional (0-D) inorganic-organic metal halides (IOMHs) have become a promising class of optoelectronic materials. Herein, we report a new photoluminescent (PL) 0-D antimony(III)-based IOMH single crystal, namely [H₂BPZ][SbCl₅]·H₂O (BPZ = benzylpiperazine). Photophysical characterizations indicate that [H₂BPZ][SbCl₅]·H₂O exhibits singlet/triplet dual-band emission. Density functional theory (DFT) calculations suggest that [H₂BPZ][SbCl₅]·H₂O has the large energy difference between singlet and triplet states, which might induce the dual emission in this compound. Temperature-dependent PL spectra analyses suggest the soft lattice and strong electron-phonon coupling in this compound. Thermogravimetric analysis shows that the water molecules in the lattice of the title crystal could be removed by thermal treatment, giving rise to a dehydrated phase of [H₂BPZ][SbCl₅]. Interestingly, such structural transformation is accompanied by a reversible PL emission transition between red light (630 nm, dehydrated phase) and yellow light (595 nm, water-containing phase). When being exposed to an environment with 77% relative humidity, the emission color of the dehydrated phase was able to change from red to yellow within 20 s, and the red emission could be restored after reheating. The red to yellow emission switching could be achieved in acetone with water concentration as low as 0.2 vol%. The reversible PL transition phenomenon makes [H₂BPZ][SbCl₅]·H₂O a potential material for luminescent water-sensing.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic-Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides

Organic-inorganic metal halides (OIMHs) have abundant optical properties and potential applications, such as light-emitting diodes, displays, solar cells, and photodetectors. Herein, we report zero-dimensional Mn-based OIMH (C₈H₂₀N)₂MnCl₄ single crystals synthesized by a simple slow evaporation method, which exhibit intense green emission at 520 nm originating from ⁴T₁-⁶A₁ transition of Mn²⁺ ions. Large organic cations in the crystal structure result in the isolated [MnCl₄]^2- tetrahedrons, and the closest Mn-Mn distance reaches 9.07 Å, which effectively inhibits the migration of excitation energy between adjacent Mn²⁺ emission centers, thus achieving a high quantum yield (∼87%) and a long photoluminescence (PL) lifetime (3.42 ms). The different optical and structural properties at low and high temperatures are revealed by temperature-dependent PL and X-ray diffraction spectra. The PL spectra and lifetimes under the heating and cooling processes indicate that the optical property transitions are reversible at 220/240 K. Our work provides a promising strategy for building multifunctional optoelectronic materials and insights into the understanding convertible photophysical properties from isomers of metal halides.

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.

Large-Area Laminar TEA2MnI4 Single-Crystal Scintillator for X-ray Imaging with Impressive High Resolution

Current X-ray imaging scintillators are dominated by inorganic scintillators grown through a high-temperature process. Exploring new types of scintillators with mild growth conditions, high light yields, and eco-friendly chemical compositions is essential and challenging. Herein, the zero-dimensional large-area laminar organic-inorganic hybrid metal halide TEA₂MnI₄ (TEA = tetraethylammonium) single crystal with dimensions of 50 mm × 60 mm × 0.82 mm is grown via a local-heating solvent evaporation method. Compared with its Cl- and Br-based counterparts, the incorporation of the iodine component enhances the X-ray attenuation ability and significantly accelerates the decay of the photoluminescence of TEA₂MnI₄. Interestingly, the prepared TEA₂MnI₄ exhibits a high transmittance of >90% over the range of 515-765 nm and exhibits a high light yield of 26288 photons/MeV, which provides the prerequisite for high-resolution X-ray imaging. The TEA₂MnI₄ single-crystal scintillator displays an astonishing spatial resolution exceeding 25 line pairs per millimeter, which provides a design concept for a Mn-I-based single crystal for high-performance scintillator applications.

Improving the Chemical Stability of Narrow-Band Green-Emitting Manganese(II) Hybrid by Zn-Doping

Hybrid tetrahedral Mn(II)-based halides show great potential for narrow-band green emitters, which could be applied in the liquid crystal display field. However, the strategy to improve the chemical stability of tetrahedral Mn hybrids has not been fully investigated. Here, we demonstrate that Zn doping can be an effective route to significantly improve the stability of tetrahedral Mn hybrids under air conditions without compromising the luminous efficiency. A new bromide (ABI)₂MnBr₄ (ABI = 2-aminobenzimidazole) is synthesized, which exhibits a typical zero-dimensional structure with isolated [MnBr₄]^2- tetrahedra in the P1̅ space group. Under 450 nm excitation, a narrow-band green-emitting peak at 516 nm is observed with a full width at half maximum of 42 nm. It is indicated that spontaneous phase transition from the tetrahedral to octahedral motif occurs in this Mn hybrid driven by humidity, combined with the emission color change from green to red. Interestingly, this phase transition could be strongly suppressed by Zn doping with a very low doping amount (5%), leading to the significantly improved chemical stability of (ABI)₂MnBr₄ without reducing the photoluminescence quantum yield. Our work provides a simple and feasible strategy to enhance the chemical stability of the green-emitting (ABI)₂MnBr₄, and it may also be applicable for other tetrahedral Mn-based hybrids.

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.

Multifunctional Chiral 2D Lead Halide Perovskites with Circularly Polarized Photoluminescence and Piezoelectric Energy Harvesting Properties

Introducing the chiral spacers to two-dimensional (2D) lead halide perovskites (LHPs) enables them to exhibit circularly polarized photoluminescence (CPPL), which could have applications in chiral-optics and spintronics. Despite that a great deal of effort has been made in this field, the reported polarization degree of CPPL at ambient conditions is still very limited, and the integration of multiple functionalities also remains to be explored. Here we report the structures, CPPL, and piezoelectric energy harvesting properties of chiral 2D LHPs, [R-1-(4-bromophenyl)ethylaminium]₂PbI₄ (R-[BPEA]₂PbI₄) and [S-1-(4-bromophenyl)ethylaminium]₂PbI₄ (S-[BPEA]₂PbI₄). Our results show that these chiral perovskites are direct bandgap semiconductors and exhibit CPPL centered at ∼513 nm with a maximum degree of polarization of up to 11.0% at room temperature. In addition, the unique configurational arrangement of the chiral spacers is found to be able to reduce the interlayer π-π interactions and consequently result in strong electron-phonon coupling. Furthermore, the intrinsic chirality of both R-[BPEA]₂PbI₄ and S-[BPEA]₂PbI₄ enables them to be piezoelectric active, and their composite films can be applied to generate voltages and currents up to ∼0.6 V and ∼1.5 μA under periodic impacting with a strength of 2 N, respectively. This work not only reports a high degree of CPPL but also demonstrates piezoelectric energy harvesting behavior for realizing multifunctionalities in chiral 2D LHPs.

Antimony -doped indium-based halide single crystals enabling white-light emission

Metal halides (TMPL)3InCl6·EtOH:xSb3+ with tunable colors were obtained by gradient Sb3+ doping. Interestingly, white emission was achieved when 0.1% of Sb3+ was employed, due to a combination of the cyan emission of organic moiety and orange emission from metal halides.

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.

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%.

Surface Ligand Engineering for a Lead-Free Cs3Cu2Br5 Microcrystal-Based Humidity Sensor with a Giant Response

Halide perovskites are potential humidity-detection materials due to their sensitivity to water, but the instability of traditional lead-based halide perovskites and the toxicity of Pb hinder further application in humidity sensing. Here, lead-free Cs₃Cu₂Br₅ perovskite microcrystals passivated by surface ligands (OLA and OAm) are used to prepare an environmentally friendly humidity sensor. The humidity sensing performance of the prepared sensors was tested, and the effect of surface ligands of perovskites on the performance of humidity sensors was analyzed. The results show that the impedance variations of the manufactured humidity sensors at 12 to 95% relative humidity are 10⁶Ω (OLA) and 10⁵Ω (OAm), respectively. Besides, the sensors demonstrated excellent repeatability, low hysteresis, and considerable stability at different RH values. Furthermore, the analysis of the different ligands attests that short-chain OLA is more conducive to the formation of porous films with stronger water absorption capacity, further improving the responsiveness of the sensor. By contrast, and long-chain OAm is more conducive to the formation of dense films, improving the response ability at low humidity. Additionally, the more hydrophilic OLA contributes to greater responsiveness, while the more hydrophobic OAm helps to shorten the response and recovery time.

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.

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.

Photo- and triboluminescent robust 1D polymers made of Mn(ii) halides and meta-carborane based bis(phosphine oxide)

The 1D CPs of [Mn(L)X₂]_n type (X = Cl, Br, I), designed on 1,7-bis(diphenylphosphinyl)-m-carborane (L), show bright phosphorescence and triboluminescence, as well as exhibit thermo- and solvatochromic luminescence.

A family of Mn(ii) complexes exhibiting strong photo- and triboluminescence as well as polymorphic luminescence

New Mn(ii) complexes supported by diphosphine dioxides exhibit strong room-temperature phosphorescence as well as bright triboluminescence and polymorphic luminescence.

Controlling information duration on rewritable luminescent paper based on hybrid antimony (III) chloride/small-molecule absorbates

Controlling the duration that information lasts on paper so that it disappears as desired is crucial for information security. However, this area is rarely studied. Here, we report [TEMA]₂SbCl₅ (1, TEMA⁺ = methyltriethylammonium), [TEA]₂SbCl₅ (2, TEA⁺ = tetraethylammonium), [TEBA]₂SbCl₅ (3, TEBA⁺ = benzyltriethylammonium), and [Ph₄P]₂SbCl₅ (4, Ph₄P⁺ = tetraphenylphosphonium) with structure-dependent reversible photoluminescent switching induced by the absorption and thermal release of small guest molecules including H₂O, methanol, and ethylene glycol. Comparing the structural disorder levels, bond lengths, and luminescent Stokes shifts of the compounds aided in understanding their selective absorption behavior. Our results indicated that the information duration on the rewritable paper coated with the title compounds is easily tuned by changing the cation of the compounds, the type of guest molecules, and laser heating power. Our study opens previously unidentified avenues for information security and extends the potential applications of rewritable paper.

Review on Sensing Applications of Perovskite Nanomaterials

Recently, perovskite-based nanomaterials are utilized in diverse sustainable applications. Their unique structural characteristics allow researchers to explore functionalities towards diverse directions, such as solar cells, light emitting devices, transistors, sensors, etc. Many perovskite nanomaterial-based devices have been demonstrated with extraordinary sensing performance to various chemical and biological species in both solid and solution states. In particular, perovskite nanomaterials are capable of detecting small molecules such as O2, NO2, CO2, etc. This review elaborates the sensing applications of those perovskite materials with diverse cations, dopants and composites. Moreover, the underlying mechanisms and electron transport properties, which are important for understanding those sensor performances, will be discussed. Their synthetic tactics, structural information, modifications and real time sensing applications are provided to promote such perovskite nanomaterials-based molecular designs. Lastly, we summarize the perspectives and provide feasible guidelines for future developing of novel perovskite nanostructure-based chemo- and biosensors with real time demonstration.