0D Perovskites: Unique Properties, Synthesis, and Their Applications

Multicolor emission from a 0D-doped hybrid halide (C8H14N2)2CdBr6 single crystal

Achieving multicolor emission is a fascinating goal that remains challenging for zero-dimensional (0D) hybrid halides. We successfully obtained a three-millimeter-scale 0D (MXDA)2CdBr6 (MXDA = C8H14N22+) single crystal (SC) by the solvothermal method. It serves as an outstanding host for doping with various valence activators, such as Cu+, Mn2+ and Sb3+, and these doped single crystals emit blue (470 nm), yellow (580 nm) and red (618 nm) fluorescence, which accurately cover a large visible region and achieve efficient multicolor emission. (MXDA)2CdBr6:8%Cu+ exhibits a high photoluminescence quantum yield (PLQY) of 60.31% under 320 nm UV excitation, while (MXDA)2CdBr6:10%Mn2+ shows a PLQY of 50.52%. Density functional theory calculations indicate that the hybrid 0D (MXDA)2CdBr6 halide is an indirect bandgap semiconductor with a bandgap value of 3.33 eV. This work expands the new material space for organic-inorganic hybrid halide materials and provides insights for tuning their optical properties.

Large-scale preparation of Sb3+-activated hybrid metal halides with efficient tunable emission from visible to near-infrared regions for advanced photonic applications

Zero-dimensional metal halides with diverse structures and rich photophysical properties have been reported. However, achieving multimode dynamic luminescence and efficient near-infrared (NIR) emission under blue light excitation in a single system is a great challenge. Herein, Sb3+-doped hybrid Cd(II) halides were synthesized by a large scale synthesis process at room temperature. Compared with the poor emission of (C12H28N)2CdX4 (C12H28N = tetrapropylammonium; X = Cl and Br) and single steady-state visible light emission of (C12H28N)2SbX5, (C12H28N)2CdX4:Sb3+ exhibits efficient tunable emission from visible to NIR regions. More specifically, (C12H28N)2CdCl4:Sb3+ exhibits distinct excitation wavelength-dependent luminescence characteristics, which can change from green to white and orange emission. Parallelly, halogen substitution can regulate the optical properties of Sb3+-doped (C12H28N)2CdCl4-xBrx (x = 0-1), which enables the excitation and emission bands to exhibit a significant redshift. Thus, the efficient broad NIR emission upon 450 nm excitation was realized in (C12H28N)2CdBr4:Sb3+. In addition, we demonstrated the use of (C12H28N)2CdCl4:Sb3+ phosphors in solid state lighting, and an advanced NIR light source was fabricated by coating (C12H28N)2CdBr4:Sb3+ on a commercial blue chip (450 nm), which exhibits the most advanced photoelectric efficiency (14.67%) and output power (32.84 mW) in hybrid metal halides. Finally, we also demonstrated the use of Sb3+-activated phosphors in four-level fluorescence anti-counterfeiting and information encryption.

Ultra-stable and Sensitive X-ray Detectors Using 3D Hybrid Perovskitoid Single Crystals

Organic-inorganic hybrid perovskites (OIHPs) have shown great potential for direct X-ray detection in security screening and medical diagnostics. However, their humidity stability is compromised due to the susceptibility of the structural components to water molecules, thereby limiting their practical application. In this work, stable and sensitive X-ray detection is achieved using high-quality bulk single crystals of the 3D perovskitoid (DMPZ)Pb2Br6 (DPB, DMPZ = N,N'-dimethyl-pyrazinium), wherein N-acid protons are replaced with hydrophobic alkyl groups. Notably, the crystals maintain phase stability after 60 days of immersion in water at room temperature, demonstrating their significant potential for moisture-stable X-ray detectors. Based on the bulk crystals of DPB, the X-ray detectors are successfully fabricated, achieving a high sensitivity of 6437.2 µC Gyair -1 cm-2 at 70 V bias and a detection limit low to 46.7 nGyair s-1, outperforming most low-dimensional perovskite detectors. Most strikingly, the detectors retain 79.6% of their initial sensitivity after 14 days of water immersion, highlighting exceptional moisture stability. This work is the first to construct moisture-stable high-performance X-ray detectors using 3D perovskitoid single crystals, advancing the development of stable X-ray detection.

Emerging 0D Hybrid Metal Halide Luminescent Glasses

0D hybrid metal halide (HMH) luminescent glasses have garnered significant attentions for its chemical diversity in optoelectronic applications and it also retains the skeleton connectivity and coordination mode of the crystalline counterparts while exhibiting various physics/chemistry characteristics distinct from the crystalline states. However, understanding of the glass-forming ability and the specific structural origins underpinning the luminescent properties of 0D HMH glasses remains elusive. In this review, it is started from the solid-liquid phase transition and thermodynamic analysis of 0D HMHs formed through melt-quenching, and summarize the current compounds capable of stably forming glassy phases via chemical structural design. The structural characterization methods are further discussed and highlight the exceptional transparency, specific luminescent properties, and glass crystallization behaviors. Moreover, the application prospects demonstrated by these 0D HMH glasses have been presented accordingly in X-ray detection and imaging, anti-counterfeiting, and information encryption. Finally, perspective is offered into the future development of this emerging family of 0D HMH glasses and their applications.

On-Off Switching of Singlet Self-Trapped Exciton Emission Endows Antimony-Doped Indium Halides with Excitation-Wavelength-Dependent Luminescence

Excitation-wavelength-dependent (Ex-De) emitters are a fascinating category of luminescent materials whose emission properties vary with the wavelength of the light used for excitation. Antimony (Sb3+)-doped indium (In)-based metal halides are efficient light emitters; however, the peak fluorescence emission of most Sb3+-activated In-halide remains independent of the excitation wavelength. Here, the study introduces a new Sb3+-doped In-halide cluster, (BDPA)2InCl5:Sb (BDPA+ = C15H18N+, benzyldimethylphenylammonium), which demonstrates efficient Ex-De emission originating from the on-off switchable fluorescence behavior of singlet self-trapped exciton (STE) in 5-coordinate Sb3+ dopant. Interestingly, when excited within the range of 240-370 nm, photoluminescence (PL) spectra of (BDPA)2InCl5:Sb show both singlet and triplet STE emission. However, under excitation wavelengths of 370 to 420 nm, the singlet STE emission is absent, resulting in a noticeable correlated color temperature change from 1700 to 3800 K. The study provides a new approach to designing color-tunable Sb3+-based luminophores, and also presents a novel application scenario for the widely recognized Sb3+ doping strategy.

Why do similar 1D-polyhedron-chain copper chloride semiconductors have 2-order-distinct luminescence quantum efficiencies?

The "green" copper halides with one-dimensional polyhedron chains are very interesting novel semiconductors. These weakly interacting parallel quantum wires (1D polyhedron chains) play key roles in their photophysical properties. Unlike Cs3Cu2I5, which has been much investigated, its homologous compounds Cs3Cu2Cl5 and CsCu2Cl3 remain less studied and their properties are controversial. Both of them are composed of specific 1D-polyhedron-chains. We report the synthesis and comparatively study the photophysical properties of the single crystals of Cs3Cu2Cl5 and CsCu2Cl3. They exhibit green and orange emissions, respectively. Surprisingly, their luminescence quantum efficiencies have a giant difference of over two orders of magnitude (96.7% vs 0.7%). The CsCu2Cl3 crystals exhibit much slower radiative transition and substantially faster nonradiative transition. The experiment in combination with the density functional theory calculation reveals that their 1D-polyhedron-chains have distinct bonding structures and degrees of distortion. This leads to different distributions of electron wave functions and different concentrations of carrier-trapping chlorine vacancies, which account for their highly contrasted quantum efficiencies. The CsCu2Cl3 and Cs3Cu2Cl5 crystals exhibit easy phase transition between each other driven by the changed temperature or ethanol erosion owing to their resembling skeleton structures of 1D polyhedral chain.

Unveiling the Antithermal Quenching Behavior in 0D Inorganic Metal Halide Cs2InCl5(H2O) Mediated by Upconversion Emission

Inorganic metal halides (IMHs) often suffer from severe fluorescence thermal quenching, limiting their application at elevated temperatures. Therefore, the exploration of IMHs exhibiting antithermal quenching (ATQ) behavior is of great importance. In this study, we developed a green synthetic route using a solvent evaporation method to successfully synthesize the 0D IMHs Cs2InCl5(H2O). By precise control over the doping ratios of Sb3+, Yb3+, and Er3+, unique dual-mode emission properties are obtained. As the temperature increases, the compound exhibited downconversion and upconversion luminescence, with relative sensitivity SR-max values of 7.11% K-1 and 1.21% K-1, respectively. Particularly anomalous is the compound's manifestation of an unconventional ATQ behavior during the upconversion process. In situ structural analysis confirmed that under high-temperature conditions, the 0D Cs2InCl5(H2O) metal halide undergoes structural evolution, transitioning through a Cs3In2Cl9 phase, which is responsible for the ATQ. This study provides experimental evidence for the abnormal ATQ of 0D metal halides, offering new inspiration for the multifunctionalization of 0D metal halides in high-temperature temperature sensing and dual-mode luminescence.

Controllable Multi-Exciton Zero-Dimensional Antimony-Based Metal Halides for White-light Emission and β-Ray Detection

Self-trapped exciton (STE) emission, typified by antimony (Sb), with broadband characteristics, represents the next generation of materials for solid-state lighting and radiation detection. However, little is known about the multiexciton behavior of the Sb emission center. Here, we proposed a general approach for designing antimony-centered multi-exciton emitting materials through self-assembly. Benefitting from controllable multiexciton behavior, dual-band white light emission spanning the entire visible spectrum was achieved. Relying on the reduction of an effective atomic number brought by self-assembly, excellent scintillation response to β-rays was attained. This study offers unprecedented insight into hybrid single/triple STE emission and unveils new avenues for single-emitter white-light emission, as well as radiographic testing using low-risk β-rays as sources.

Recent advances in artificial neuromorphic applications based on perovskite composites

High-performance perovskite materials with excellent physical, electronic, and optical properties play a significant role in artificial neuromorphic devices. However, the development of perovskites in microelectronics is inevitably hindered by their intrinsic non-ideal properties, such as high defect density, environmental sensitivity, and toxicity. By leveraging materials engineering, integrating various materials with perovskites to leverage their mutual strengths presents great potential to enhance ion migration, energy level alignment, photoresponsivity, and surface passivation, thereby advancing optoelectronic and neuromorphic device development. This review initially provides an overview of perovskite materials across different dimensions, highlighting their physical properties and detailing their applications and metrics in two- and three-terminal devices. Subsequently, we comprehensively summarize the application of perovskites in combination with other materials, including organics, nanomaterials, oxides, ferroelectrics, and crystalline porous materials (CPMs), to develop advanced devices such as memristors, transistors, photodetectors, sensors, light-emitting diodes (LEDs), and artificial neuromorphic systems. Lastly, we outline the challenges and future research directions in synthesizing perovskite composites for neuromorphic devices. Through the review and analysis, we aim to broaden the utilization of perovskites and their composites in neuromorphic research, offering new insights and approaches for grasping the intricate physical working mechanisms and functionalities of perovskites.

A 0D Ge(II)-Halide-Based Perovskite with Enhanced Semiconducting Behavior for Electronic Capacitors

Perovskite materials have surged to the forefront of materials science, captivating researchers worldwide with their distinctive crystal lattice arrangement and remarkable optical, electric and dielectric attributes. The current study focuses on the development of a novel zero-dimensional (0D) Ge(II)-based hybrid perovskite, formulated as NH3(CH2)2NH3GeF6, and synthesized through a gradual evaporation process conducted at room temperature. The crystal structure is characterized by an arrangement of organic cations and isolated octahedral [GeF6]2- groups. This configuration is stabilized by relatively weak intermolecular bonds. A comprehensive analysis of the material's thermal properties using differential scanning calorimetry (DSC) revealed a distinct phase transition occurring at approximately 323 K, which was further confirmed through electrical measurements. The studied compound provided a broad absorption range across the visible spectrum and an optical band gap of 3.30 eV, indicating its potential for semiconducting applications in optoelectronic devices. Photoluminescence PL analysis displays a blueish broad-band emission with a high color rendering index CRI value of 91, when excited at 325 nm. This emission primarily originates from the self-trapped excitons (STEs) recombination in the inorganic [GeF6]2-. Herein, the temperature-dependent behavior of grain conductivity exhibited an Arrhenius-type pattern, with an activation energy (E a) of 0.46 eV, confirming the semiconductor nature of the investigated compound. In addition, a deep investigation of the alternating current conductivity, analyzed using Jonscher's law, demonstrates that the conduction mechanism is effectively described by the correlated barrier hopping (CBH) model. The dielectric performances show a significant dielectric constant (ε' ∼ 103). Thus, all these interesting physical properties of this hybrid perovskite have paved the way for advancements in various technological applications, particularly in the field of electronic capacitors.

Organic-Inorganic Hybrid Cuprous-Based Metal Halides with Unique Two-Dimensional Crystal Structure for White Light-Emitting Diodes

Ternary cuprous (Cu+)-based metal halides, represented by cesium copper iodide (e.g., CsCu2I3 and Cs3Cu2I5), are garnering increasing interest for light-emitting applications owing to their intrinsically high photoluminescence quantum yield and direct band gap. Toward electrically driven light-emitting diodes (LEDs), it is highly desirable for the light emitters to have a high structural dimensionality as it may favor efficient electrical injection. However, unlike lead-based halide perovskites whose light-emitting units can be facilely arranged in three-dimensional (3D) ways, to date, nearly all ternary Cu+-based metal halides crystallize into 0D or 1D networks of Cu-X (X=Cl, Br, I) polyhedra, whereas 3D and even 2D structures remain mostly uncharted. Here, by employing a fluorinated organic cation, we report a new kind of ternary Cu+-based metal halides, (DFPD)CuX2 (DFPD+=4,4-difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr2, which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr2 crystals show appealing properties, including improved ambient stability and an efficient warm white-light emission, making it a promising candidate for single-component lighting and display applications.

Unveiling Chirality Transfer between Chiral Centers and Metal Halides in Chiral Organic-Inorganic Hybrid Metal Halides

Chirality transfer refers to the process in which chiral cations compel the crystallization of the inorganic component into the Sohncke group. Enhancing the chirality of the inorganic component in chiral organic-inorganic hybrid metal halides (OIHMHs) through chirality transfer, aimed at improving chiroptical and spintronic properties, remains challenging due to the complexity of the underlying mechanism. To investigate this, we propose a novel concept─chirality transfer coefficient─as a means of quantifying the strength of chirality transfer in OIHMHs. A comparative study of OIHMHs with varying dimensionality, metal ions, and chiral centers was conducted to elucidate this mechanism. By analyzing factors such as hydrogen bonding, the number of chiral centers, dimensionality, helical geometry, and structural distortions, we found that chirality transfer is influenced by a combination of structural dimensions and the number of chiral centers. Importantly, our findings reveal that 0D, and 1D OIHMHs, particularly 1D with a zigzag chain configuration, exhibit stronger chirality transfer than their 2D counterparts. Moreover, in 2D OIHMHs, a reduction in the number of chiral centers enhances chirality transfer. However, no direct correlation was observed between chirality transfer and spin splitting. These insights contribute to a more comprehensive understanding of chirality transfer mechanisms and provide a strategic approach for enhancing the chirality transfer and associated physical properties in OIHMHs.

Metal halide perovskite polymer composites for indirect X-ray detection

Metal halide perovskites (MHPs) have emerged as a promising class of materials for radiation detection due to their high atomic numbers and thus high radiation absorption, tunable and efficient luminescent properties and simple solution processability. Traditional MHP scintillators, however, suffer from environmental degradation, spurring interest in perovskite-polymer composites. This paper reviews recent developments in these composites tailored for scintillator applications. It discusses various synthesis methods, including solution-based and mechanochemical techniques, that enable the formation of composites with enhanced performance metrics such as light yield, detection limit, and environmental stability. The review also covers the remaining challenges and opportunities in fabrication techniques and performance metric evaluations of this class of materials. By offering a comprehensive overview of current research and future perspectives, this paper underscores the potential of perovskite-polymer composites to revolutionize the field of radiation detection.

Boosting circularly polarized luminescence by optimizing off-centering octahedral distortion in zero-dimensional hybrid indium-antimony halides

Chiral zero-dimensional hybrid metal halides (0D HMHs) are being extensively studied as they can directly generate circularly polarized luminescence (CPL) with high photoluminescence quantum yields (PLQYs), yet improving their luminescence dissymmetry factor (g lum) remains a challenge. This study proposes a general strategy to boost the g lum value of chiral 0D HMHs by optimizing the off-centering distortion of inorganic octahedra. Accordingly, (R/S-MBA)2(2MA)In0.95Sb0.05Cl6 (MBA = α-methylbenzylammonium, 2MA = dimethylamine) and (R/S-MBA)2(3MA)In0.95Sb0.05Cl6 (3MA = trimethylamine) with near-unity PLQYs are accordingly synthesized. With increasing the from 0.012 to 0.020, the |g lum| is accordingly increased from 7.8 × 10-3 to 2.0 × 10-2. Notably, the |g lum| can be further boosted to an impressive value of 3.8 × 10-2 while maintaining near-unity PLQYs by continuously increasing the . Experimental results reveal that the choice of achiral ligands and varied Sb3+ dopant concentrations can modulate the distribution and strength of hydrogen bonds around indium-antimony halogen octahedra, respectively, thus regulating the parameter of octahedra in 0D hybrid metal halides. Additionally, light-emitting diodes with a polarization of 1.6% are fabricated. This work sheds light on the relationship between the distortion of inorganic octahedra and the g lum value.

Solution Synthesis and Light-Emitting Applications of One-Dimensional Lead-Free Cerium(III) Metal Halides

Combining rare earth elements with the halide perovskite structure offers valuable insights into designing nonlead (Pb) luminescent materials. However, most of these compositions tend to form zero-dimensional (0D) networks of metal-halide polyhedra, with higher-dimensional (1D, 2D, and 3D) structures receiving relatively less exploration. Herein, we present synthesis and optical properties of Cs3CeCl6·3H2O, characterized by its unique 1D crystal structure. The conduction band minimum of Cs3CeCl6·3H2O becomes less localized as a result of the increased structural dimension, making it possible for the materials to achieve an efficient electrical injection. For both Cs3CeCl6·3H2O single crystals and nanocrystals, we also observed remarkable luminescence with near-unity photoluminescence quantum yield and exceptional phase stability. Cs3CeCl6·3H2O single crystals demonstrate an X-ray scintillation light yield of 31900 photons/MeV, higher than that of commercial LuAG:Ce (22000 photons/MeV); electrically driven light-emitting diodes fabricated with Cs3CeCl6·3H2O nanocrystals yield the characteristic emission of Ce3+, indicating their potential use in next-generation violet-light-emitting devices.

Tuning the dimensionality in chiral and racemic organic/tin hybrids with halides

Chiral 1D tin iodides EBASnI3 were synthesized while incorporating enantiomerically pure and racemic ethylbenzylammonium (EBA) cations between the 1D shared inorganic corners. The dimensionality was reduced to 0D when replacing iodine with bromine. In all the cases, the presence of hydrogen bonds was observed between the organic part and the inorganic part, while transfer of chirality was evidenced for the EBASnI3 enantiomerically pure compounds.

Ion-Exchanging Lead-Free Perovskite with Tunable Emission Wavelengths for Chemical and Fluorescent Double-Modal Anticounterfeiting Application

Novel and covert fluorescence is quite desirable for fluorescent anticounterfeiting application. Here, Cs2InCl5·H2O/Sb and Cs2NaInCl6/Sb with high photoluminescence quantum yields (PLQYs) of 99.61 and 99.9%, respectively, were achieved. Considering the excellent optical performances together with the high similarity of the two crystal structures, we tried to realize the crystal structure transition from Cs2InCl5·H2O/Sb to Cs2NaInCl6/Sb by an ion-exchange method. It was well done by just adding the NaCl precursor with different concentrations in the Cs2InCl5·H2O/Sb product. Interestingly, a gradual color change from yellow to orange, warm white, white, cool white, and blue was achieved in the process of crystal structure transition. The energy-transfer dynamic models of Cs2InCl5·H2O/Sb, the white product, and Cs2NaInCl6/Sb were identified. The chemical reaction and UV fluorescence properties made it possible for application in chemical and fluorescent double-modal anticounterfeiting and highly decreased the possibility of being cracked and copied. Especially, when salt for daily cooking was used to replace NaCl, a similar phenomenon happened as that of the 99.9% NaCl precursor, which made it easy to be applicated. The combination of chemical and optical verifications provides two levels of security and unbreakable encryption. The results demonstrate that the transition from Cs2InCl5·H2O/Sb to Cs2NaInCl6/Sb is highly promising in fluorescent anticounterfeiting application.

Highly Selective Protic-Solvent-Mediated Organic-Inorganic Hybrid Cuprous Bromides Achieving Structural Transformation

The potential application of stimuli-responsive hybrid copper halides in information storage and switch devices has generated significant interest. However, their transformation mechanism needs to be further studied deeply. Herein, two zero-dimensional (0D) organic-inorganic hybrids, namely, (TBA)CuBr2 (1) with linear [CuBr2]- units and (TBA)2Cu4Br6 (2) with [Cu4Br6]2- clusters (TBA+ = (C4H9)4N+), are synthesized using simple solvent evaporation approaches. Interestingly, upon exposure to distinct protic solvents, such as methanol, ethanol, ethylene glycol, or hot water, 1 undergoes a transformation into 2 with varying degrees of transition, accompanied by a change in luminescence color from cyan to orange (or mixed color) under high-energy emission (e.g., 254 nm) excitation. Hot water can trigger 1 to completely transform into 2 because of its large contact angle difference in the solvents. Furthermore, 2 can be converted back to 1 through a simple solid-state mechanochemical reaction. Additionally, the structure of 2 remains unchanged even after immersion in 80 °C H2O for 168 h due to the dense organic framework. This study provides valuable insights for exploring reversible structural transformation materials in the 0D metal halide system.

High-efficiency color-tunable ultralong room-temperature phosphorescence from organic-inorganic metal halides via synergistic inter/intramolecular interactions

Materials exhibiting highly efficient, ultralong and multicolor-tunable room-temperature phosphorescence (RTP) are of practical importance for emerging applications. However, these are still very scarce and remain a formidable challenge. Herein, using precise structure design, several novel organic-inorganic metal-halide hybrids with efficient and ultralong RTP have been developed based on an identical organic cation (A). The original organic salt (ACl) exhibits red RTP properties with low phosphorescence efficiency. However, after embedding metals into the organic salt, the changed crystal structure endows the resultant metal-halide hybrids with excellent RTP properties. In particular, A2ZnCl4·H2O exhibits the highest RTP efficiency of up to 56.56% with a long lifetime of up to 159 ms. It is found that multiple inter/intramolecular interactions and the strong heavy-atom effect of the rigid metal-halide hybrids can suppress molecular motion and promote the ISC process, resulting in highly stable and localized triplet excitons followed by highly efficient RTP. More crucially, multicolor-tunable fluorescence and RTP achieved by tuning the metal and halogen endow these materials with wide application prospects in the fields of multilevel information encryption and dynamic optical data storage. The findings promote the development of phosphorescent metal-halide hybrids for potential high-tech applications.

Theoretical Design of Tellurium-Based Two-Dimensional Perovskite Photovoltaic Materials

In recent years, the photoelectric conversion efficiency of three-dimensional (3D) perovskites has seen significant improvements. However, the commercial application of 3D perovskites is hindered by stability issues and the toxicity of lead. Two-dimensional (2D) perovskites exhibit good stability but suffer from low efficiency. Designing efficient and stable lead-free 2D perovskite materials remains a crucial unsolved scientific challenge. This study, through structural prediction combined with first-principles calculations, successfully predicts a 2D perovskite, CsTeI5. Theoretical calculations indicate that this compound possesses excellent stability and a theoretical efficiency of up to 29.3%, showing promise for successful application in thin-film solar cells. This research provides a new perspective for the design of efficient and stable lead-free 2D perovskites.

Quantum-confined bismuth iodide perovskite nanocrystals in mesoporous matrices

Bismuth iodide perovskite nanocrystals are considered a viable alternative to the Pb halide ones due to their reduced toxicity and increased stability. However, it is still challenging to fabricate nanocrystals with a small and controlled size, and their electronic properties are not well understood. Here, we propose the growth of Bi iodide perovskite nanocrystals using different mesoporous silica with ordered pores of controlled diameter as templates. We obtain a series of confined Cs3Bi2I9 and MA3Bi2I9 perovskites with diameters of 2.3, 3.7, 7.4, and 9.2 nm, and precise size control. The complex absorption spectra of the encapsulated perovskites cannot be properly fitted using classical Tauc or Elliott formalisms. By fitting the spectra with a modified Elliott formula, the bandgap values and exciton binding energies (70-400 meV) could be extracted. The calculated bandgaps scale with the pore sizes. Using a combined experimental and theoretical approach, we demonstrate for the first time quantum confinement in 0D Bi-iodide perovskite nanocrystals.

Three-State Dielectric Switching within a Narrow Temperature Range in Isopropylammonium Lead Iodide, a One-Dimensional Perovskite with Polar Phase

The phenomenon of dielectric switching has garnered considerable attention due to its potential applications in electronic and photonic devices. Typically, hybrid organic-inorganic perovskites, HOIPs, exhibit a binary (low-high) dielectric state transition, which, while useful, represents only the tip of the iceberg in terms of functional relevance. One way to boost the versatility of applications is the discovery of materials capable of nonbinary switching schemes, such as three-state dielectric switching. The ideal candidate for that task would exhibit a trio of attributes: two reversible, first-order phase transitions across three distinct crystal phases, minimal thermal hysteresis, and pronounced, step-like variations in dielectric permittivity, with a substantial change in its real part. Here, we demonstrate a one-dimensional lead halide perovskite with the formula (CH3)2C(H)NH3)PbI3, abbreviated as ISOPrPbI3, that fulfills these criteria and demonstrates three-state dielectric switching within a narrow temperature range of ca. 45 K. Studies on ISOPrPbI3 also revealed the polar nature of the low-temperature phase III below 266 K through pyrocurrent experiments, and the noncentrosymmetric character of the intermediate phase II and low-temperature phase III is confirmed via second harmonic generation measurements. Additionally, luminescence studies of ISOPrPbI3 have demonstrated combined broadband and narrow emission properties. The introduction of ISOPrPbI3 as a three-state dielectric switch not only addresses the limitations posed by the wide thermal gap between dielectric states in previous materials but also opens new avenues for the development of nonbinary dielectric switchable materials.

Self-Trapped Exciton Emission in Highly Polar 0D Hybrid Ammonium/Hydronium-Based Perovskites Triggered by Antimony Doping

Various monovalent cations are employed to construct metal halide perovskites with various structures and functionalities. However, perovskites based on highly polar A-site cations have seldom been reported. Here, a novel hybrid 0D (NH4)x(OH3)3-xInCl6 perovskite with highly polar hydronium OH3+ cations is introduced in this study. Upon doping with Sb3+, hybrid 0D (NH4)x(OH3)3-xInCl6 single crystals exhibited highly efficient broadband yellowish-green (550 nm) and red (630 nm) dual emissions with a PLQY of 86%. The dual emission arises due to Sb3+ occupying two sites within the crystal lattice that possess different polarization environments, leading to distinct Stokes shift energies. The study revealed that lattice polarity plays a significant role in the self-trapped exciton emission of Sb3+-doped perovskites, contributing up to 25% of the Stokes shift energy for hybrid 0D (NH4)x(OH3)3-xInCl6:Sb3+ as a secondary source, in addition to the Jahn-Teller deformation. These findings highlight the potential of Sb3+-doped perovskites for achieving tunable broadband emission and underscore the importance of lattice polarity in determining the emission properties of perovskite materials.

Flexible, photoluminescent 0D Cs4PbX6 (X = Br, Br/I)-PMMA composite films for white LED via water-induced recrystallization

3D CsPbX3 inorganic perovskite materials have attracted much attention in optoelectronic devices because of their strong absorbance, high photoluminescent quantum yield, tunable band gap, and narrow emission bandwidth. However, their practical usefulness is limited due to their poor stability in ambient conditions. Here, we created photoluminescent 0D Cs4PbX6 (X = Br, Br/I) suspensions in toluene by adding a small amount of water. The photoluminescent 0D Cs4PbX6 perovskite was mixed with polymethylmethacrylate (PMMA) forming 0D Cs4PbX6/PMMA composite films with higher PL, stability, transparency, and transmittance than that of the 3D CsPbX3/PMMA composite films prepared separately. Moreover, the PL intensity maintains 90% of the initial value after 30 days in water, showing excellent water stability. The flexible white-light LED device prepared by the composite films illustrated good luminescence performance with color rendering index 74.77, chromaticity coordinates (0.32, 0.33), and color temperature 6997 K.

Graphical abstract

Modulation of Nucleation and Growth Kinetics of Perovskite Nanocrystals Enables Efficient and Spectrally Stable Pure-Red Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) based on CsPb(Br/I)3 nanocrystals (NCs) usually suffer from severe spectral instability under operating voltage due to the poor-quality PeNCs. Herein, zeolite was utilized to prepare high-quality CsPb(Br/I)3 NCs via promoting the homogeneous nucleation and growth and suppressing the Ostwald ripening of PeNCs. In addition, the decomposed zeolite interacted strongly with PeNCs through Pb-O bonds and hydrogen bonds, which inhibited the formation of defects and suppressed halide ion migration, leading to an improved photoluminescence quantum yield (PLQY) and enhanced stability of PeNCs. Moreover, the strong binding affinity of decomposed zeolite to PeNCs contributed to the formation of homogeneous perovskite films with high PLQY. As a result, pure-red PeLEDs with Commission International de I'Eclairage (CIE) coordinates of (0.705, 0.291) were fabricated, approaching the Rec. 2020 red primary color. The devices achieved a peak external quantum efficiency of 23.0% and outstanding spectral stability.

Exploiting halide perovskites for heavy metal ion detection

Heavy metal ions such as mercury (Hg), copper (Cu), and cadmium (Cd) pose significant threats to ecosystems and human health due to their toxicity and bioaccumulation potential. With growing environmental concerns over heavy metal ion pollution, there is an urgent need to develop efficient detection methods for safeguarding public health and the environment. Various materials, including polymers, nanomaterials, and porous substances, have been used for heavy metal ion detection and have shown promising performance for different scenarios. However, each of these materials has certain limitations as probes. Metal halide perovskites (MHPs), known for their exceptional optoelectronic properties and high structural and chemical tunability, have gained great attention in applications such as photovoltaics and LEDs. Yet, their potential as metal ion probes remains rarely explored. This review assesses MHPs as prospective materials for heavy metal ion detection, taking their structure, chemical properties, and responses to external stimuli into consideration. Three key detection mechanisms-cation exchange (CE), electron transfer (ET), and fluorescence resonance energy transfer (FRET), are explored to understand how metal ions trigger fluorescence changes on perovskites, enabling their detection. Finally, current avenues of developing perovskite probes are discussed, which include exploration of lead-free perovskites to mitigate environmental concerns arising from lead leakage and the pursuit of achieving high-sensitivity and stable detection in aqueous media, summarizing the existing and promising strategies in this field.

Structural Phase Transition in 0D (3,5-DMP)2Bi1-xSbxCl5 Metal Halides: Expression of the Lone Pair Effect and Polyhedral Distortion

Low-dimensional Bi/Sb-based organic-inorganic metal halides (OIMHs) have attracted immense attention from the research community because of their structural diversity and efficient luminescence properties. Further understanding of the relationship between the structure and luminescence properties of these materials is of utmost importance for tuning the luminescence properties for various practical applications. Herein, we have synthesized two lead-free Bi/Sb-based novel OIMHs, (3,5-DMP)2BiCl5 and (3,5-DMP)2SbCl5 [(3,5-DMP) = 3,5-dimethylpiperidine], with zero-dimensional (0D) structures and crystallizing in triclinic (P1 ¯ space group) and monoclinic (P21/c space group) crystal systems, respectively. Both the compounds behave as typical semiconductors with indirect optical band gaps of 3.34 and 3.36 eV for pristine Bi and Sb compounds. These compounds exhibit higher environmental and thermal stability at ambient conditions. Gradual substitution of Sb at the Bi site in (3,5-DMP)2Bi1-xSbxCl5 resulted in the introduction of structural strain due to the significant expression of the lone pair effect, thus leading to a structural transition from the triclinic to monoclinic phase. The effect of the structural phase transition on the optical properties is also studied in (3,5-DMP)2Bi1-xSbxCl5. This work may offer new direction and guidance for exploring various 0D hybrid metal halides and tuning the structures for improvement in the luminescence properties.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

Unveiling Sb3+ Doping and Tricolor Luminescence from Intrinsic Self-Trapped Excitons in Cs2ZnCl4 Crystals

Zero-dimensional (0D) lead-free halide perovskites have lately received significant interest owing to their captivating broadband emissions. An in-depth understanding of the luminescence mechanism of self-trapped excitons (STEs) and realization of effective regulation of luminescence properties have become a major challenge in the research of lead-free metal halides. Herein, we have synthesized the Cs2ZnCl4 and Sb3+-doped Cs2ZnCl4 crystals and conducted a comprehensive investigation into their distinct electronic structures and optical characteristics. The findings from both experimental and theoretical investigations indicate that the tricolor luminescence in Cs2ZnCl4 and blue emission in Sb3+-doped Cs2ZnCl4 stem from intrinsic STEs, and the near-infrared emission originates from extrinsic STEs associated with the Sb3+ ion in Sb3+-doped Cs2ZnCl4. Sb3+ doping increases the quantum yield of Cs2ZnCl4 to a large extent. In addition, intersystem crossing, exciton self-trapping, and lattice relaxation are the main reasons for the large Stokes shift. The present study is expected to provide a novel perspective for researchers in comprehending the luminescent mechanism of STEs and advancing the utilization of 0D lead-free metal halides in optoelectronic applications.

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.

Lead-Free Chiral Perovskite for High Degree of Circularly Polarized Light Emission and Spin Injection

We report a zero-dimensional (0D) lead-free chiral perovskite (S-/R-MBA)4Bi2I10 with a high degree of circularly polarized light (CPL) emission. Our 0D lead-free chiral perovskite exhibits an average degree of circular polarization (DOCP) of 19.8% at 78 K under linearly polarized laser excitation, and the maximum DOCP can reach 25.8%, which is 40 times higher than the highest DOCP of 0.5% in all reported lead-free chiral perovskites to the best of our knowledge. The high DOCP of (S-/R-MBA)4Bi2I10 is attributed to the free exciton emission with a Huang-Rhys factor of 2.8. In contrast, all the lead-free chiral perovskites in prior reports are dominant by self-trapped exciton in which the spin relaxation reduces DOCP dramatically. Moreover, we realize the manipulation of the valley degree of freedom of monolayer WSe2 by using the spin injection of the 0D chiral lead-free perovskites. Our results provide a new perspective to develop lead-free chiral perovskite devices for CPL light source, spintronics, and valleytronics.

Mapping Uncharted Lead-Free Halide Perovskites and Related Low-Dimensional Structures

Research on perovskites has grown exponentially in the past decade due to the potential of methyl ammonium lead iodide in photovoltaics. Although these devices have achieved remarkable and competitive power conversion efficiency, concerns have been raised regarding the toxicity of lead and its impact on scaling up the technology. Eliminating lead while conserving the performance of photovoltaic devices is a great challenge. To achieve this goal, the research has been expanded to thousands of compounds with similar or loosely related crystal structures and compositions. Some materials are "re-discovered", and some are yet unexplored, but predictions suggest that their potential applications may go beyond photovoltaics, for example, spintronics, photodetection, photocatalysis, and many other areas. This short review aims to present the classification, some current mapping strategies, and advances of lead-free halide double perovskites, their derivatives, lead-free perovskitoid, and low-dimensional related crystals.

A 0D hybrid lead-free halide with near-unity photoluminescence quantum yield toward multifunctional optoelectronic applications

Zero-dimensional (0D) hybrid metal halides have emerged as highly efficient luminescent materials, but integrated multifunction in a structural platform remains a significant challenge. Herein, a new hybrid 0D indium halide of (Im-BDMPA)InCl6·H2O was designed as a highly efficient luminescent emitter and X-ray scintillator toward multiple optoelectronic applications. Specifically, it displays strong broadband yellow light emission with near-unity photoluminescence quantum yield (PLQY) through Sb3+ doping, acting as a down-conversion phosphor to fabricate high-performance white light emitting diodes (WLEDs). Benefiting from the high PLQY and negligible self-absorption characteristics, this halide exhibits extraordinary X-ray scintillation performance with a high light yield of 55 320 photons per MeV, which represents a new scintillator in 0D hybrid indium halides. Further combined merits of a low detection limit (0.0853 μGyair s-1), ultra-high spatial resolution of 17.25 lp per mm and negligible afterglow time (0.48 ms) demonstrate its excellent application prospects in X-ray imaging. In addition, this 0D halide also exhibits reversible luminescence off-on switching toward tribromomethane (TBM) but fails in any other organic solvents with an ultra-low detection limit of 0.1 ppm, acting as a perfect real-time fluorescent probe to detect TBM with ultrahigh sensitivity, selectivity and repeatability. Therefore, this work highlights the multiple optoelectronic applications of 0D hybrid lead-free halides in white LEDs, X-ray scintillation, fluorescence sensors, etc.

In-situ free-standing inorganic 2D Cs2PbI2Cl2 nanosheets for efficient self-powered photodetectors with carbon electrode

Inorganic two-dimensional (2D) perovskites possess excellent thermal stability and high charge mobility, making them an attractive choice for stable optoelectronic devices such as photodetectors (PDs). The formation of an appropriate inorganic 2D perovskite structure is of great importance to efficient PDs, especially to that of planar self-powered photovoltaic PDs featuring perpendicular charge transport channels. Herein, we implemented morphological engineering on wide bandgap inorganic 2D perovskite, Cs2PbI2Cl2, demonstrating a successful preparation of in-situ free-standing nanosheets structure with proper charge channels for photovoltaic type self-powered PDs. Compared with its counterpart with a nanoblock morphology, the 2D nanosheet Cs2PbI2Cl2 film exhibits enhanced charge mobility and purified Ruddlesden-Popper phase that can withstand high-energy electron beam radiation, accelerated thermal aging and long-term shelf storage. Sandwiching Cs2PbI2Cl2 nanosheet film in between tin oxide (SnO2) and polythiophene (P3HT) as electron and hole acceptors, respectively, the constructed photovoltaic type structure exhibits effective dissociation of excitons at the cascade type-II interface. The nanosheets enable lower dark current and more efficient charge collection than the nanoblock structure. As a result, the self-powered photodetectors with 2D Cs2PbI2Cl2 nanosheets deliver an outstanding responsivity of 698 mW/cm2 and a detectivity of 8.6×1012 Jones. The stable PDs can be applied to monitor ultraviolet irradiation in real outdoor conditions. Our work demonstrates the significant role of morphology tuning of 2D inorganic perovskite in stable, cost-effective and efficient photodetectors.

Hybrid Iodide Perovskites of Divalent Alkaline Earth and Lanthanide Elements

Hybrid halide perovskites AMIIX3 (A = ammonium cation, MII = divalent cation, X = Cl, Br, I) have been extensively studied but have only previously been reported for the divalent carbon group elements Ge, Sn, and Pb. While they have displayed an impressive range of optoelectronic properties, the instability of GeII and SnII and the toxicity of Pb have stimulated significant interest in finding alternatives to these carbon group-based perovskites. Here, we describe the low-temperature solid-state synthesis of five new hybrid iodide perovskites centered around divalent alkaline earth and lanthanide elements, with the general formula AMIII3 (A = methylammonium, MA; MII = Sr, Sm, Eu, and A = formamidinium, FA; MII = Sr, Eu). Structural, calorimetric, optical, photoluminescence, and magnetic properties of these materials are reported.

Pressure-Regulated Excitonic Transitions in Emergent Metal Halides

ConspectusEmergent metal halides are generating significant interest as novel optical materials, and their diverse applications have brought them to the spotlight of chemistry and material science. The optical properties of semiconducting metal halides are fundamentally dominated by excitonic transitions, which refer to the complex processes of excitonic formation, self-trapping, as well as subsequent transitions of intersystem crossing (ISC) and internal conversion (IC). In this regard, high pressure has recently opened a new research dimension to regulate excitonic transitions in metal halides via continuous structural modulations, to understand the intriguing excitonic emissions from a new perspective. In this Account, we aim to rationalize the fundamental strategy for modulating and optimizing the optical properties of metal halides based on delicate exciton regulation via high-pressure method. First, the band gaps of metal halides that are directly related to the efficiency of excitonic formation, are accurately modulated through contraction, distortion, and destruction of metal-halogen polyhedra under compression. Then, considerable enhancement of self-trapped exciton emission is demonstrated by inducing proper polyhedral distortions via high-pressure method. Furthermore, the emission energy of metal halides could also be controllably and widely tuned through pressure-modulated excitonic transitions. Upon compression on different metal halides, excitonic IC is promoted with sufficient polyhedral distortions, and different sets of ISC could also be achieved. In the end, we emphasize the significance of high-pressure investigations in uncovering the complex excitonic transitions in emergent metal halides and predicting novel metal halides with desired optical properties at ambient conditions. It is expected that these discussions could inspire researchers in different fields to perform interdisciplinary high-pressure studies on novel functional materials.

In Situ Real-Time Observation of Formation and Self-Assembly of Perovskite Nanocrystals at High Temperature

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have received much attention due to their outstanding optical and electronic properties, but the underlying growth mechanism remains elusive due to their rapid formation process. Here, we report an in situ real-time study of the growth of Cs4PbBr6 NCs under practical synthesis conditions in a custom-made reactor. Through the synchrotron-based small-angle X-ray scattering technique, we find that the formation of Cs4PbBr6 NCs is accomplished in three steps: the fast nucleation process accompanied by self-focusing growth, the subsequent diffusion-limited Ostwald ripening, and the self-assembly of NCs into the face-centered cubic (fcc) superlattices at high temperature and the termination of growth. The simultaneously collected wide-angle X-ray scattering signals further corroborate the three-step growth model. The influence of superlattice formation is also elucidated, which improves the uniformity of the final NCs.

Tellurium-Doped 0D Organic-Inorganic Hybrid Lead-Free Perovskite for X-ray Imaging

The application of X-ray imaging in military, industrial flaw detection, and medical examination is inseparable from the wide application of scintillator materials. In order to substitute for lead, lower costs, and reduce self-absorption, organic-inorganic hybrid lead-free perovskite scintillators are emerging as a new option. In this work, novel (TEA)2Zr1-xTexCl6 perovskite microcrystals (MCs) were successfully synthesized by a hydrothermal method, with Te4+ doping, which leads to yellow triplet-state self-trapped excitons emission. The emission peak of (TEA)2Zr1-xTexCl6 located at 605 nm under X-ray excitation, which was applied to X-ray imaging, shows a clear wiring structure inside the USB connector. The detection limit (DL) of 820 nGyair/s for (TEA)2Zr0.9Te0.1Cl6 is well below the dose rate corresponding to a standard medical X-ray diagnosis is 5.5 μGyair/s. This work opens up a new path for organic-inorganic hybrid lead-free scintillators.

Dimension Tuning of All-Inorganic Ag-Based Metal Halides by Solvent Engineering

Dimension growth of metal halides is important for its properties and applications. However, such dimension control of the metal halides is rarely reported in the literature and the growth mechanism is not clear yet. A minute difference of solvent properties can tremendously alter the process of nucleation and growth of crystals. Herein, an intriguing phenomenon of dimension tuning for Ag-based metal halides is reported. The 1D Cs2 AgCl3 crystals can be obtained in pure DMF while the 2D CsAgCl2 crystals are obtained in pure DMSO. Both exhibit bright yellow emission, which are derived from self-trapping excitons (STEs). The photoluminescence quantum yield (PLQY) of Cs2 AgCl3 (1D) and CsAgCl2 (2D) are 28.46 % and 20.61 %, respectively. In order to understand the mechanism of the dimension change, additional solvents (N,N-dimethylacetamide, DMAC, 1,3-Dimethyl-Tetrahydropyrimidin-2(1H)-one, DMPU) are also selected to process the precursor for crystal growth. By comparing the functional group, dielectric constant, and donor number among the four solvents, we find the donor number plays the predominant role in nucleation process for Cs2 AgCl3 and CsAgCl2 . This research reveals the relationship between coordination ability of the solvent and the dimension of metal halides.

In situ recrystallization of zero-dimensional hybrid metal halide glass-ceramics toward improved scintillation performance

Zero-dimensional (0D) hybrid metal halide (HMH) glasses are emerging luminescent materials and have gained attention due to their transparent character and ease of processing. However, the weakening of photoluminescence quantum efficiency from crystal to glass phases poses limitations for photonics applications. Here we develop high-performance glass-ceramic (G-C) scintillators via in situ recrystallization from 0D HMH glass counterparts composed of distinct organic cations and inorganic anions. The G-C scintillators maintain excellent transparency and exhibit nearly 10-fold higher light yields and lower detection limits than those of glassy phases. The general in situ recrystallization within the glass component by a facile heat treatment is analyzed via combined experimental elaboration and structural/spectral characterization. Our results on the development of G-Cs can initiate more exploration on the phase transformation engineering in 0D HMHs, and therefore make them highly promising for large-area scintillation screen applications.

Metal-Free Perovskites for X-Ray Detection

Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials' stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.

Temperature Dependent Hydrogen Bond Toward High Emission in an Emerging Indium-Based Perovskite

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) with broadband emission attract immense scientific interest due to their potential application for the next generation of solid-state lighting. However, due to low exciton utilization, organic cations generally adjust structure rather than contribute the band edge to affect optical properties. Based on this, OIHPs are usually allowed to obtain a low photoluminescence quantum yield (PLQY). Herein, a good charge transfer carrier (p-phenylenediamine, PPDA) as organic cation is rationally employed and a novel indium-based perovskite is synthesized. By coupling with H2 O molecules, a strong interaction between organic and inorganic components is realized by hydrogen bonding, which has good transportability and greatly improves the exciton utilization. The regions of hydrogen bonding show high electron mobility, combined with the induced recombination center, improving the progress of charge relaxation. As a result, the regulation of hydrogen bond strength based on the microstructure optimization directly determines the optical emission intensity, realizing nearly 100% PLQY. Further, the polyhydrogen bond structure makes each component a stronger interaction, showing high stability in polar, organic, and acidic solvent, as well as long-term storing, which represents one of the highest overall performances for lighting in OIHPs.

Nature of Self-Trapped Exciton Emission in Zero-Dimensional Cs2ZrCl6 Perovskite Nanocrystals

Low dimensional perovskite-inspired materials with self-tapped exciton (STE) emission have stimulated a surge of cutting-edge research in optoelectronics. Despite numerous efforts on developing versatile low-dimensional perovskite-inspired materials with efficient STE emissions, there is little emphasis on the intrinsic dynamics of STE-based broad emission in these materials. Here, we investigated the excited state dynamics in zero-dimensional (0D) Cs2ZrCl6 nanocrystals (NCs) with efficient blue STE emission. By using femtosecond transient absorption (fs-TA) spectroscopy, the ultrafast STE formation process within 400 fs is directly observed. Then, the formed STEs relax to an intermediate STE state with a lifetime of ∼180 ps before reaching the emissive STE state with a lifetime of ∼15 μs. Our work offers a comprehensive and precise dynamic picture of STE emission in low-dimensional metal halides and sheds light on extending their potential applications.

Lead-Free Halide Perovskites for Direct X-Ray Detectors

Lead halide perovskites have made remarkable progress in the field of radiation detection owing to the excellent and unique optoelectronic properties. However, the instability and the toxicity of lead-based perovskites have greatly hindered its practical applications. Alternatively, lead-free perovskites with high stability and environmental friendliness thus have fascinated significant research attention for direct X-ray detection. In this review, the current research progress of X-ray detectors based on lead-free halide perovskites is focused. First, the synthesis methods of lead-free perovskites including single crystals and films are discussed. In addition, the properties of these materials and the detectors, which can provide a better understanding and designing satisfactory devices are also presented. Finally, the challenge and outlook for developing high-performance lead-free perovskite X-ray detectors are also provided.

Structure-Related Evolution of Magnetic Order in Anisidinium Tetrachlorocuprates(II)

Tetrachlorocuprate(II) hybrids of the three anisidine isomers (ortho-, meta-, and para-, or 2-, 3-, and 4-methoxyaniline, respectively) were prepared and studied in the solid state via X-ray diffraction and magnetization measurements. Depending on the position of the methoxy group of the organic cation, and subsequently, the overall cation geometry, a layered, defective layered, and the structure comprising discrete tetrachlorocuprate(II) units were obtained for the para-, meta-, and ortho-anisidinium hybrids, respectively. In the case of layered and defective layered structures, this affords quasi-2D-layered magnets, demonstrating a complex interplay of strong and weak magnetic interactions that lead to the long-range ferromagnetic (FM) order. In the case of the structure with discrete CuCl₄^2- ions, a peculiar antiferromagnetic (AFM) behavior was revealed. The structural and electronic origins of magnetism are discussed in detail. To supplement it, the method for calculation of dimensionality of the inorganic framework as a function of interaction length was developed. The same was used to discriminate between n-dimensional and "almost" n-dimensional frameworks, to estimate the organic cation geometry limits for layered halometallates, and to provide additional reasoning behind the observed relation between cation geometry and framework dimensionality, as well as their relation to differences in magnetic behavior.

Two-Dimensional Metal Halides for X-Ray Detection Applications

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.

Emerging Halide Perovskite Ferroelectrics

Halide perovskites have gained tremendous attention in the past decade owing to their excellent properties in optoelectronics. Recently, a fascinating property, ferroelectricity, has been discovered in halide perovskites and quickly attracted widespread interest. Compared with traditional perovskite oxide ferroelectrics, halide perovskites display natural advantages such as structural softness, low weight, and easy processing, which are highly desirable in applications pursuing miniaturization and flexibility. This review focuses on the current research progress in halide perovskite ferroelectrics, encompassing the emerging materials systems and their potential applications in ferroelectric photovoltaics, self-powered photodetection, and X-ray detection. The main challenges and possible solutions in the future development of halide perovskite ferroelectric materials are also attempted to be pointed out.

Halide Double Perovskite Nanocrystals Doped with Rare-Earth Ions for Multifunctional Applications

Most lead-free halide double perovskite materials display low photoluminescence quantum yield (PLQY) due to the indirect bandgap or forbidden transition. Doping is an effective strategy to tailor the optical properties of materials. Herein, efficient blue-emitting Sb³⁺ -doped Cs₂ NaInCl₆ nanocrystals (NCs) are selected as host, rare-earth (RE) ions (Sm³⁺ , Eu³⁺ , Tb³⁺ , and Dy³⁺ ) are incorporated into the host, and excellent PLQY of 80.1% is obtained. Femtosecond transient absorption measurement found that RE ions not only served as the activator ions but also filled the deep vacancy defects. Anti-counterfeiting, optical thermometry, and white-light-emitting diodes (WLEDs) are exhibited using these RE ions-doped halide double perovskite NCs. For the optical thermometry based on Sm³⁺ -doped Cs₂ NaInCl₆ :Sb³⁺ NCs, the maximum relative sensitivity is 0.753% K^-1 , which is higher than those of most temperature-sensing materials. Moreover, the WLED fabricated by Sm³⁺ -doped Cs₂ NaInCl₆ :Sb³⁺ NCs@PMMA displays CIE color coordinates of (0.30, 0.28), a luminous efficiency of 37.5 lm W^-1 , a CCT of 8035 K, and a CRI over 80, which indicate that Sm³⁺ -doped Cs₂ NaInCl₆ :Sb³⁺ NCs are promising single-component white-light-emitting phosphors for next-generation lighting and display technologies.

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

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

The Tetrel Bond and Tetrel Halide Perovskite Semiconductors

The ion pairs [Cs+•TtX3-] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX3, that are widely regarded as blockbuster materials for optoelectronic applications such as in solar cells. The 3D structures consist of an anionic inorganic tetrel halide framework stabilized by the cesium cations (Cs+). We use computational methods to show that the geometrical connectivity between the inorganic monoanions, [TtX3-]∞, that leads to the formation of the TtX64- octahedra and the 3D inorganic perovskite architecture is the result of the joint effect of polarization and coulombic forces driven by alkali and tetrel bonds. Depending on the nature and temperature phase of these perovskite systems, the Tt···X tetrel bonds are either indistinguishable or somehow distinguishable from Tt-X coordinate bonds. The calculation of the potential on the electrostatic surface of the Tt atom in molecular [Cs+•TtX3-] provides physical insight into why the negative anions [TtX3-] attract each other when in close proximity, leading to the formation of the CsTtX3 tetrel halide perovskites in the solid state. The inter-molecular (and inter-ionic) geometries, binding energies, and charge density-based topological properties of sixteen [Cs+•TtX3-] ion pairs, as well as some selected oligomers [Cs+•PbI3-]n (n = 2, 3, 4), are discussed.