Lead-Free Zero-Dimensional Organic-Copper(I) Halides as Stable and Sensitive X-ray Scintillators

Embedding Te4+ into Sn4+-Based Metal Halide To Passivate Structure Defects for High-Performance Light-Emitting Application

Low-dimensional lead-halide hybrids are an emerging class of optical functional material but suffer the problems of toxicity and poor air stability. Among lead-free metal halides, tin(IV)-based metal halides are promising optoelectronic materials due to their robust structure and environmental friendliness. However, their photoluminescence (PL) properties are poor, and the underlying mechanisms are still elusive. Herein, a stable Sn4+-based halide hybrid, (C4H7N2)2SnCl6, was developed, which however exhibits poor PL properties at room temperature (RT) due to the lattice defects and the robust crystal structure. To enhance its PL efficiency, the Te4+ ion with a stereoactive 5s2 lone pair has been introduced into the lattice. As a result, Te4+-doped (C4H7N2)2SnCl6 displays broadband orange emission (∼640 nm) with a PL efficiency of ∼46% at RT. Interestingly, Te4+-doped (C4H7N2)2SnCl6 shows triple emission bands at 80 K, which could be due to the synergistic effect of the organic cations and the self-trapped state induced by Te4+. Additionally, high-performance white light-emitting diodes were prepared using Te4+-doped (C4H7N2)2SnCl6, revealing the potential of this material for lighting applications. This study provides new insight into the PL mechanism of Sn4+-based metal-halide hybrids and thus facilitates the design and development of eco-friendly light-emitting metal halides.

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.

Revealing the Structure-Luminescence Relationship in Robust Sn(IV)-Based Metal Halides by Sb3+ Doping

Low-dimensional hybrid metal halides are an emerging class of materials with highly efficient photoluminescence (PL), but the problems of poor stability remain challenging. Sn(IV)-based metal halides show robust structure but exhibit poor PL properties, and the structure-luminescence relationship is elusive. Herein, two Sn(IV)-based metal halides (compounds 1 and 2) with the same constituent ((C6H16N2)SnCl6) but different crystal structures have been prepared, which however show poor PL properties at room temperature due to the absence of active ns2 electrons. To improve materials' PL properties, Sb3+ with active 5s2 electrons was embedded into the lattice of Sn4+-based hosts. As a result, efficient emissions were achieved for Sb3+-doped compounds 1 and 2 with a maximum PL efficiency of 14.28 and 62%, respectively. Experimental and calculation results reveal that the smaller distorted lattice structure of the host could result in the blueshift of the emission from Sb3+. Thus, a tunable color from red to orange was realized. Benefiting from the broadband efficient emission from Sb3+-doped compound 2, an efficient white light-emitting diode with a high color rendering index of up to 92.3 was fabricated to demonstrate its lighting application potential. This work promotes the understanding of the influence of robust Sn(IV)-based host lattice on the PL properties of Sb3+, advancing the development of environmentally friendly, low-cost, and high-efficiency Sn(IV)-based metal halides.

Dual-color photoluminescence modulation of zero-dimensional hybrid copper halide microcrystals

Zero-dimensional hybrid copper(I) halides (HCHs) are attractive due to their interesting photoluminescence (PL) properties and the high abundance and low toxicity of copper. In this study, we report green-red dual emission from rhombic 1-butyl-1-methyl piperidinium copper bromide [(Bmpip)2Cu2Br4] microcrystals (MCs) prepared on borosilicate glass. The structure and elemental composition of the MCs are characterized by single crystal X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Interestingly, MCs prepared on an ITO-coated glass plate show an intense green emission compared to the dual emission on a bare glass or plastic substrate. Furthermore, the intensity of the green emission from the MC is enormously increased by powdering using a conductive material, suggesting the deactivation of the red-emitting state by a charge transfer interaction with the conductor. These findings open a new strategy to suppress the self-trapping of excitons by longitudinal optical phonons and control the dual emitting states in HCHs.

Synthesis and Characterization of New Hybrid Organic-Inorganic Metal Halides [(CH3)3SO]M2I3 (M = Cu and Ag)

Recently, all-inorganic copper(I) metal halides have emerged as promising optical materials due to their high light emission efficiencies. This work details the crystal structure of the two hybrid organic-inorganic metal halides [(CH3)3SO]M2I3 (M = Cu and Ag) and their alloyed derivatives [(CH3)3SO]Cu2-xAgxI3 (x = 0.2; 1.25), which were obtained by incorporating trimethylsulfoxonium organic cation (CH3)3SO+ in place of Cs+ in the yellow-emitting all-inorganic CsCu2I3. These compounds are isostructural and centrosymmetric with the space group Pnma, featuring one-dimensional edge-sharing [M2I3]- anionic double chains separated by rows of (CH3)3SO+ cations. Based on density functional theory calculations, the highest occupied molecular orbitals (HOMOs) of [(CH3)3SO]M2I3 (M = Cu and Ag) are dominated by the Cu or Ag d and I p orbitals, while the lowest unoccupied molecular orbitals (LUMOs) are Cu or Ag s and I p orbitals. [(CH3)3SO]Cu2I3 single crystals exhibit a semiconductor resistivity of 9.94 × 109 Ω·cm. Furthermore, a prototype [(CH3)3SO]Cu2I3 single-crystal-based X-ray detector with a detection sensitivity of 200.54 uCGy-1 cm-2 (at electrical field E = 41.67 V/mm) was fabricated, indicating the potential use of [(CH3)3SO]Cu2I3 for radiation detection applications.

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.

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.

Centimeter-Sized Single Crystals of Dion-Jacobson Phase Lead-Free Double Perovskite for Efficient X-ray Detection

2D Dion-Jacobson (DJ) phase hybrid perovskites have shown great promise in the photoelectronic field owing to their outstanding optoelectronic performance and superior structural rigidity. However, DJ phase lead-free double perovskites are still a virgin land with direct X-ray detection. Herein, we have designed and synthesized a new DJ phase lead-free layered double perovskite of (HIS)2 AgSbBr8 (1, HIS2+  = histammonium). Centimeter-sized (18 × 10 × 5 mm3 ) single crystals of 1 are successfully grown via the temperature cooling technique, exhibiting remarkable semiconductive characteristics such as a high resistivity (2.2 × 1011  Ω cm), a low trap state density (3.56 × 1010 cm-3 ), and a large mobility-lifetime product (1.72 × 10-3 cm2 V-1 ). Strikingly, its single-crystal-based X-ray detector shows a high sensitivity of 223 µC Gy-1 air cm-2 under 33.3 V mm-1 , a low detection limit (84.2 nGyair s-1 ) and superior anti-fatigue. As far as we know, we firstly demonstrates the potential of 2D DJ phase lead-free hybrid double perovskite in X-ray detection, showing excellent photoelectric response and operational stability. This work will pave a promising pathway to the innovative application of hybrid perovskites for eco-friendly and efficient X-ray detection.

One-Dimensional Hybrid Copper(I) Iodide Single Crystal with Renewable Scintillation Properties

Low-dimensional hybrid copper(I) halides attract considerable attention in the field of light emissions. In this work, we obtained the centimeter-sized single crystal of 1,3-propanediamine copper(I) iodide (PDACuI₃) with a solvent evaporation method. The single crystal X-ray diffraction of PDACuI₃ reveals that the [CuI₄] tetrahedra form the corner-connected chains separated by PDAs, forming a one-dimensional structure with an orthorhombic space group of Pbca. The band gap is determined to be 4.03 eV, and the room temperature photoluminescence (PL) quantum yield is determined to be 26.5%. The thermal quenching and negative thermal quenching of emission are observed via temperature-dependent PL spectra, and our study shows that the intermediate nonradiative state below the self-trapped exciton state may get involved in these temperature-dependent behaviors. The X-ray scintillation performance of PDACuI₃ single crystals is also evaluated, and the relative light output renewed to 94.3% of the fresh one after a low-temperature annealing. On the basis of our results, PDACuI₃ single crystals provide nontoxicity and renewable scintillation performance, thus showing potential application in the area of low-cost radiation detectors.

Molecular Sensitization Enabled High Performance Organic Metal Halide Hybrid Scintillator

Scintillators, one of the essential components in medical imaging and security checking devices, rely heavily on rare-earth-containing inorganic materials. Here, a new type of organic-inorganic hybrid scintillators containing earth abundant elements that can be prepared via low-temperature processes is reported. With room temperature co-crystallization of an aggregation-induced emission (AIE) organic halide, 4-(4-(diphenylamino) phenyl)-1-(propyl)-pyrindin-1ium bromide (TPA-PBr), and a metal halide, zinc bromide (ZnBr₂ ), a zero-dimensional (0D) organic metal halide hybrid (TPA-P)₂ ZnBr₄ with a yellowish-green emission peaked at 550 nm has been developed. In this hybrid material, dramatically enhanced X-ray scintillation of TPA-P⁺ is achieved via the sensitization by ZnBr₄ ^2- . The absolute light yield (14,700 ± 800 Photons/MeV) of (TPA-P)₂ ZnBr₄ is found to be higher than that of anthracene (≈13,500 Photons/MeV), a well-known organic scintillator, while its X-ray absorption is comparable to those of inorganic scintillators. With TPA-P⁺ as an emitting center, short photoluminescence and radioluminescence decay lifetimes of 3.56 and 9.96 ns have been achieved. Taking the advantages of high X-ray absorption of metal halides and efficient radioluminescence with short decay lifetimes of organic cations, the material design paves a new pathway to address the issues of low X-ray absorption of organic scintillators and long decay lifetimes of inorganic scintillators simultaneously.

Exceptional structural diversity of hybrid halocuprates(I) with methylammonium and formamidinium cations

Hybrid halocuprates(I) are nowadays the subject of intensive studies as promising materials for various optoelectronic applications. This class of materials is characterized by wide structural diversity enabled by a great variety in the size and shape of organic cations. Therefore, the study of composition-structure-property relationships is a key step for the rational design of new halocuprate materials with desired properties. In this paper, we comprehensively studied MABr/CuBr and FABr/CuBr systems (MA⁺ = methylammonium and FA⁺ = formamidinium) and established the existence of five novel phases (namely, MACu₂Br₃, FA₂[Cu₄Br₆], MACuBr₂, FACuBr₂, and FA₃CuBr₄) related to four different structural types and three distinct A⁺ : Cu⁺ stoichiometries (A⁺ = MA⁺/FA⁺). The optical properties of the discovered phases are studied by absorption and low-temperature photoluminescence spectroscopy. Based on a crystal-chemical analysis, we explained a unique structural diversity of the MA- and FA-based bromocuprates, as well as revealed new structure-property relationships.

Facile synthesis of Sb3+-doped (Bmim)2InCl5(H2O) through a grinding method for light-emitting diodes

Organic-inorganic metal hybrid halides (OIMHs) as a new kind of photoelectric material have gained much attention in recent years because of their excellent performance in solid-state lighting applications. However, the preparation of most OIMHs is complex and requires a long preparation time in addition to the solvent providing the reaction environment. This greatly limits their further applications. Here, we synthesized zero-dimensional lead-free OIMH (Bmim)₂InCl₅(H₂O) (Bmim = 1-butyl-3-methylimidazolium) by a facile grinding method at room temperature. Through Sb³⁺ doping, Sb³⁺:(Bmim)₂InCl₅(H₂O) shows a bright broadband emission centered at 618 nm under UV excitation, which could be attributed to the self-trapped exciton (STE) emission of Sb³⁺ ions. To explore their ability in the field of solid-state lighting, a white-light-emitting diode (WLED) device based on Sb³⁺:(Bmim)₂InCl₅(H₂O) with a high color rendering index of 90 was fabricated. This work enriches In³⁺-based OIMHs and provides a new direction for the simple fabrication of OIMHs.

Solvent-Free Grinding Synthesis of Hybrid Copper Halides for White Light Emission

Lead-free metal halides (LMHs) have recently attracted numerous attention in solid-state lighting due to their unique structures and outstanding optoelectronic properties. However, conventional preparation processes with the utilization of toxic organic solvents and high temperatures seem to impede commercial applications of LMHs. In this work, we successfully synthesize Cu⁺-based metal halides (TMA)₃Cu₂Br_5-xCl_x (TMA: tetramethylammonium) with high photoluminescence quantum yields (PLQYs) via a solvent-free mechanical grinding method. By changing the ratio of halide ions (Cl^- and Br^-) in precursors, the emission wavelength of the prepared (TMA)₃Cu₂Br_5-xCl_x can be tuned from 535 to 587 nm, which are employed as emitters in the fabrication of white-light-emitting diodes (WLEDs). The achieved WLEDs exhibit a high color rendering index value of 84 and standard Commission Internationale de l'Éclairage (CIE) coordinates of (0.324, 0.333). This feasible and solvent-free preparation strategy not only promotes the mass production of LMHs but also highlights the promising potential for efficient solid-state illumination.

Copper Organometallic Iodide Arrays for Efficient X-ray Imaging Scintillators

Lead-free organic metal halide scintillators with low-dimensional electronic structures have demonstrated great potential in X-ray detection and imaging due to their excellent optoelectronic properties. Herein, the zero-dimensional organic copper halide (18-crown-6)₂Na₂(H₂O)₃Cu₄I₆ (CNCI) which exhibits negligible self-absorption and near-unity green-light emission was successfully deployed into X-ray imaging scintillators with outstanding X-ray sensitivity and imaging resolution. In particular, we fabricated a CNCI/polymer composite scintillator with an ultrahigh light yield of ∼109,000 photons/MeV, representing one of the highest values reported so far for scintillation materials. In addition, an ultralow detection limit of 59.4 nGy/s was achieved, which is approximately 92 times lower than the dosage for a standard medical examination. Moreover, the spatial imaging resolution of the CNCI scintillator was further improved by using a silicon template due to the wave-guiding of light through CNCI-filled pores. The pixelated CNCI-silicon array scintillation screen displays an impressive spatial resolution of 24.8 line pairs per millimeter (lp/mm) compared to the resolution of 16.3 lp/mm for CNCI-polymer film screens, representing the highest resolutions reported so far for organometallic-based X-ray imaging screens. This design represents a new approach to fabricating high-performance X-ray imaging scintillators based on organic metal halides for applications in medical radiography and security screening.

Zero-Dimensional Hybrid Cuprous Halide of [BAPMA]Cu2Br5 as a Highly Efficient Light Emitter and an X-Ray Scintillator

Lead halide perovskites have been explored as a new kind of promising X-ray with wide applications in radiation-associated fields, but low light yield and serious toxicity extremely restrict further applications. To address these issues, we herein demonstrated one new zero-dimensional (0D) organic-inorganic hybrid cuprous halide of [BAPMA]Cu₂Br₅ (BAPMA = N,N-Bis(3-aminopropyl) methylamine) containing discrete [Cu₄Br₁₀]^6- tetramers as excellent lead-free scintillators. Upon UV light excitation, [BAPMA]Cu₂Br₅ displays highly efficient broadband yellowish-green light emission with one dominant peak at 526 nm, a large Stokes shift of 244 nm, and a high photoluminescent quantum yield of 53.40%. Significantly, this broadband light emission can also be excited by higher-energy X-ray as radioluminescence with a high scintillation light yield of 43,744 photons/MeV. The detection limit of 0.074 μGy_air/s is also far less than the required value for regular medical diagnostics of 5.5 μGy_air/s. The solution-assembled hybrid structure facilely enables the [BAPMA]Cu₂Br₅-based scintillation screen to display high-performance X-ray imaging with a spatial resolution of 15.79 lp/mm showcasing potential application in X-ray radiography. In brief, combined merits of low toxicity and cost, negligible self-absorption, a low detection limit, considerable light yield, and spatial resolution highlight the excellent scintillation performance of 0D hybrid cuprous halide.

Fiber Optic Plate Coupled Pb-Free Perovskite X-ray Camera Featuring Low-Dose-Rate Imaging toward Dental Diagnosis

Copper-based halide perovskites have been considered as promising scintillators. However, they still cannot meet the requirement of low-dose-rate X-ray imaging in medical diagnosis. Herein, we design a fiber optic plate (FOP) coupled perovskite X-ray camera to reduce the dose rate toward dental X-ray imaging. Tl doped Cs₃Cu₂I₅ prepared via molten salt reaction has a high light yield of 72,000 photons/MeV, resulting from Tl₁⁰/Tl₂⁰-self-trapped hole emissions. After FOP coupling, the pulp cavity, root canal, dentin and root canal file can be clearly observed under a low dose rate as low as 3 μGy_air s^-1, which is absolutely lower than the required 5.5 μGy_air s^-1 for commercial intraoral dental sensors. The realization of such a low dose rate is attributed to the high coupling efficiency of 75% for the FOP and the high brightness of 262 lm m^-2 for the scintillation screen. This designed portable X-ray camera shows its huge potential in intraoral dental X-ray imaging.

Realizing High-Efficiency Yellow Emission of Organic Antimony Halides via Rational Structural Design

Zero-dimensional (0D) organic metal halides have captured extensive attention for their various structures and distinguished optical characteristics. However, achieving efficient emission through rational crystal structure design remains a great challenge, and how the crystal structure affects the photophysical properties of 0D metal halides is currently unclear. Herein, a rational crystal structure regulation strategy in 0D Sb(III)-based metal halides is proposed to realize near-unity photoluminescence quantum yield (PLQY). Specifically, two 0D organic Sb(III)-based compounds with different coordination configurations, namely, (C₂₅H₂₂P)₂SbCl₅ and (C₂₅H₂₂P)SbCl₄ (C₂₅H₂₂P⁺ = benzyltriphenylphosphonium), were successfully obtained by precisely controlling the ratio of the initial raw materials. (C₂₅H₂₂P)₂SbCl₅ adopts an octahedral coordination geometry and shows highly efficient broadband yellow emission with a PLQY of 98.6%, while (C₂₅H₂₂P)SbCl₄ exhibits a seesaw-shaped [SbCl₄]^- cluster and does not emit light under photoexcitation. Theoretical calculations reveal that, by rationally controlling the coordination structure, the indirect bandgap of (C₂₅H₂₂P)SbCl₄ can be converted to the direct bandgap of (C₂₅H₂₂P)₂SbCl₅, thus ultimately boosting the emission intensity. Together with efficient emission and outstanding stability of (C₂₅H₂₂P)₂SbCl₅, a high-performance white-light emitting diode (WLED) with a high luminous efficiency of 31.2 lm W^-1 is demonstrated. Our findings provide a novel strategy to regulate the coordination structure of the crystals, so as to rationally optimize the luminescence properties of organic metal halides.