2D Metal Halide Research Articles

Utilizing 2D metal halide perovskite thin films as highly tuneable surfaces for orientation control of energetic materials

Perovskites were utilized as a tunable layer to control crystallization and preferential orientation of energetic material thin films.

Tellurium(IV) Halide Achieving Effective Nonlinear-Optical Activity: The Role of Chiral Ligands and Lattice Distortion.

Chiral organic-inorganic hybrid metal halides are a promising class of nonlinear-optical materials with unique optical properties and flexible crystal structures. However, the structures and properties of chiral hybrid tellurium halides, especially second harmonic generation (SHG), have not been reported. Here, by introducing chiral organic molecule (R/S)-methylbenzylammonium (R/S-MBA), we synthesized a pair of novel zero-dimensional (0D) chiral tellurium-based hybrid halides with noncentrosymmetric space group C2, (R/S-MBA)2TeCl6 (R/S-Cl). Single-crystal X-ray diffraction analysis and solid-state circular dichroism (CD) spectra confirm that R/S-Cl shows obvious enantiomer enrichment. Moreover, the resulting chiral products present an efficient SHG response. Interestingly, through manipulation of halogen atoms, two pairs of achiral tellurium halides, (R/S-MBA)2TeBr6 (R/S-Br) and (R/S-MBA)2TeI6 (R/S-I), were obtained, both of which crystallize in the centrosymmetric space group R3̅. It is noteworthy that R/S-I has a narrow band gap of 1.55 eV, which is smaller than that of most 0D metal halides and comparable to that of three-dimensional lead halide, showing its potential as a highly efficient light absorber.

Tuning Structure and Excitonic Properties of 2D Ruddlesden-Popper Germanium, Tin, and Lead Iodide Perovskites via Interplay between Cations.

The compositional tunability of 2D metal halide perovskites enables exploration of diverse semiconducting materials with different structural features. However, rationally tuning the 2D perovskite structures to target physical properties for specific applications remains challenging, especially for lead-free perovskites. Here, we study the effect of the interplay of the B-site (Ge, Sn, and Pb), A-site (cesium, methylammonium, and formamidinium), and spacer cations on the structure and optical properties of a new series of 2D Ruddlesden-Popper perovskites using the previously unreported spacer cation 4-bromo-2-fluorobenzylammonium (4Br2FBZ). We report eight new crystal structures and study the consequence of varying the B-site (Pb, Sn, Ge) and dimension (n = 1, 2, vs 3D). Dimension strongly influences local distortion and structural symmetry, and the increased octahedral tilting and lone pair effects in Ge perovskites lead to a polar n = 2 perovskite that exhibits second harmonic generation, (4Br2FBZ)2(Cs)Ge2I7. In contrast, the analogous Sn and Pb perovskites remain centrosymmetric, but the B-site metal influences the photoluminescence properties. The Pb perovskites exhibit broad, defect-mediated emission at low temperature, whereas the Sn perovskites show purely excitonic emission over the entire temperature range, but the carrier recombination dynamics depend on dimensionality and dark excitonic states. Wholistic understanding of these differences that arise based on cations and dimensionality can guide the rational materials design of 2D perovskites for targeting physical properties for optoelectronic applications based on the interplay of cations and the connectivity of the inorganic framework.

Antimony-Triggered Tunable White Light Emission in Lead-Free Zero-Dimensional Indium Halide with Ultrastable CCT of White Light Emitting Diodes.

A highly efficient and easily tunable luminescence is significant for solid-state luminescent (SSL) materials. However, achieving a photoluminescence quantum yield (PLQY) close to unity and tuning the emission remain challenging tasks. Metal doping strategies enable resolution of these issues. Herein, we report the preparation of a novel organic-inorganic lead-free indium-based metal halide hybrid (MP)3InCl6•EtOH (MP = C4H10ON) with a typical zero-dimension structure. When excited at 320 nm, (MP)3InCl6•EtOH exhibits a dual emission band at 420 and 600 nm, which originates from the organic cation [MP] and the [InCl6]3- octahedral unit. The photoluminescence can be significantly enhanced through Sb3+ doping, resulting in an increase in PLQY from 0.78% to near unity. Multiple emission color tunings have been achieved by regulating the Sb doping level and the radiation wavelength, resulting in a change in emission color from blue → white → orange. Optical characterizations reveal that the significantly enhanced emission centered at 600 nm can be attributed to more efficient absorption, closely associated with an additional 1S0 → 3P1 transition in the inorganic octahedron [In(Sb)Cl6]3- due to Sb3+ doping. With its excellent optical performance, a white light emitting diode (WLED) has been successfully fabricated by coating the mixture of (MP)3InCl6•EtOH:15%Sb3+ with blue phosphor BaMgAl10O17:Eu2+ onto a UV LED chip. The WLED device exhibits perfect white light emission with regard to the International Commission on Illumination (CIE) coordinates of (0.36, 0.34). Significantly, the WLED device maintains a stable correlated color temperature (CCT) range of 4119-4393 K and CIE coordinates (x: 0.37-0.34, y: 0.35-0.33) as the driven current varies from 20 to 200 mA, demonstrating outstanding stability across different power levels. This work not only presents a novel system for achieving remarkably enhanced luminescent performance and tuning emission bands in 0D metal halides but also represents a significant step toward achieving resistance to color drifting for stable WLEDs.

Achieving Highly Efficient Orange Emission in Tin (IV)‐Based Metal Halides with Outstanding Anti‐Water Stability Through Antimony Doping and Reasonable Structural Modulation

AbstractRecently, 0D metal halides have attracted widespread interest because of their diverse structures and rich luminescence properties. Nevertheless, the controllable synthesis of metal halide clusters with the ideal configuration using chemical methods remains a great challenge. In addition, the relationship between the coordination configuration and the optical properties of 0D metal halides is not well understood. In this study, two homologous Sb3+‐doped 0D Sn (IV)‐based metal halides with different coordination configurations are developed by inserting a single organic ligand, tetrabutylphosphonium chloride (TBPCl), into a SnCl4 lattice, resulting in different optical properties. Under photoexcitation, Sb3+‐doped (TBP)SnCl5·DMF shows a negligible luminescence from the organic cation of TBP+, while Sb3+‐doped (TBP)2SnCl6 shows a bright orange emission band at 650 nm with a photoluminescence quantum yield (PLQY) of 99%. The above two compounds show quite different optical properties, which should be due to the too‐large lattice distortion of Sb3+‐doped (TBP)SnCl5·DMF, and the DMF will cause the efficient non‐radiation relaxation. In particular, Sb3+‐doped (TBP)2SnCl6 exhibits remarkable anti‐water stability, which shows stability in water for 48 h without structural degradation, and the luminous intensity remains at a high level. Combined with its excellent optical properties and impressive stability, Sb3+‐doped (TBP)2SnCl6 is used in white‐light‐emitting diodes (WLED).

Assembling Two Self‐Trapped Exciton Emissions in 0D Metal Halides with Near‐Unity Quantum Yield and Zero Thermal‐Quenching Photoluminescence

AbstractZero‐dimensional (0D) lead‐free metal halides with efficient photoluminescence (PL) have wide application prospects in the optoelectronics field due to their unique structures and physicochemical properties. However, thermal quenching seriously hinders the practical applications of metal halide materials. Herein, this challenging effort is spearheaded to design novel lead‐free 0D indium‐based chloride K3InCl6:Sb3+ single crystals with zero‐thermal quenching and a near‐unity PL quantum yield based on an effective strategy to suppress non‐radiative transitions. Experimental and computational studies indicate that the intense PL emission originates from self‐trapping excitons (STEs). The extremely low temperature of 7 K and time‐resolved spectra reveal the existence of two individual STEs emissions induced by the distinguished octahedrons in K3InCl6:Sb3+ crystals. Meanwhile, the K3InCl6:Sb3+ crystals can maintain PL stability without thermal quenching over a wide temperature range. Furthermore, the phosphor‐converted light‐emitting diodes can stably operate in the long term, benefitting from the significant structural and PL stability of Sb3+‐doped 0D indium‐based chlorides. Therefore, this work not only presents new 0D metal halides with high efficiency and remarkable stability, but also provides insights into designing high‐performance optoelectronic materials.

A Self-Powered UV Photodetector With Ultrahigh Responsivity Based on 2D Perovskite Ferroelectric Films With Mixed Spacer Cations.

Self-powered photodetectors (PDs) have the advantages of no external power requirement, wireless operation, and long life. Spontaneous ferroelectric polarizations can significantly increase built-in electric field intensity, showing great potential in self-powered photodetection. Moreover, ferroelectrics possess pyroelectric and piezoelectric properties, beneficial for enhancing self-powered PDs. 2D metal halide perovskites (MHPs), which have ferroelectric properties, are suitable for fabricating high-performance self-powered PDs. However, the research on 2D metal halide perovskites ferroelectrics focuses on growing bulk crystals. Herein, 2D ferroelectric perovskite films with mixed spacer cations for self-powered PDs are demonstrated by mixing Ruddlesden-Popper (RP)-type and Dion-Jacobson (DJ)-type perovskite. The (BDA0.7 (BA2 )0.3 )(EA)2 Pb3 Br10 film possesses, overall, the best film qualities with the best crystalline quality, lowest trap density, good phase purity, and obvious ferroelectricity. Based on the ferro-pyro-phototronic effect, the PD at 360nm exhibits excellent photoelectric properties, with an ultrahigh peak responsivity greater than 93 A W-1 and a detectivity of 2.5 × 1015 Jones, together with excellent reproducibility and stability. The maximum responsivities can be modulated by piezo-phototronic effect with an effective enhancement ratio of 480%. This work will open up a new route of designing MHP ferroelectric films for high-performance PDs and offers the opportunity to utilize it for various optoelectronics applications.

Intense Hydrochromic Photon Upconversion from Lead-Free 0D Metal Halides For Water Detection and Information Encryption.

Hydrochromic materials that change their luminescence color upon exposure to moisture have attracted considerable attention owing to their applications in sensing and information encryption. However, the existing materials lack high hydrochromic response and color tunability. This study reports the development of a new and bright 0D Cs3 GdCl6 metal halide as the host for hydrochromic photon upconversion in the form of polycrystals (PCs) and nanocrystals. Lanthanides co-doped cesium gadolinium chloride metal halides exhibit upconversion luminescence (UCL) in the visible-infrared region upon 980nm laser excitation. In particular, PCs co-doped with Yb3+ and Er3+ exhibit hydrochromic UCL color change from green to red. These hydrochromic properties are quantitatively confirmed through the sensitive detection of water in tetrahydrofuran solvent via UCL color changes. This water-sensing probe exhibits excellent repeatability and is particularly suitable for real-time and long-term water monitoring. Furthermore, the hydrochromic UCL property is exploited for stimuli-responsive information encryption via cyphertexts. These findings will pave the way for the development of new hydrochromic upconverting materials for emerging applications, such as noncontact sensors, anti-counterfeiting, and information encryption.

Study of Glass Formation and Crystallization Kinetics in a 2D Metal Halide Perovskite Using Ultrafast Calorimetry.

While crystalline 2D metal halide perovskites (MHPs) represent a well-celebrated semiconductor class, supporting applications in the fields of photovoltaics, emitters, and sensors, the recent discovery of glass formation in an MHP opens many new opportunities associated with reversible glass-crystalline switching, with each state offering distinct optoelectronic properties. However, the previously reported [S-(-)-1-(1-naphthyl)ethylammonium]2PbBr4 perovskite is a strong glass former with sluggish glass-crystal transformation time scales, pointing to a need for glassy MHPs with a broader range of compositions and crystallization kinetics. Herein we report glass formation for low-melting-temperature 1-MeHa2PbI4 (1-MeHa = 1-methyl-hexylammonium) using ultrafast calorimetry, thereby extending the range of MHP glass formation across a broader range of organic (fused ring to branched aliphatic) and halide (bromide to iodide) compositions. The importance of a slight loss of organic and hydrogen iodide components from the MHP in stabilizing the glassy state is elucidated. Furthermore, the underlying kinetics of glass-crystal transformation, including activation energies, crystal growth rate, Angell plot, and fragility index, is studied using a combination of kinetic, thermodynamic, and rheological modeling techniques. An inferred fast crystal growth rate of 0.21 m/s for 1-MeHa2PbI4 shows promise toward suitability in extended application spaces, for example, in metamaterials, nonvolatile memory, and optical and neuromorphic computing devices.

Turning Self‐Trapped Exciton Emission to Near‐Infrared Region in Thermochromism Zero‐Dimensional Hybrid Metal Halides

AbstractLow dimensional lead‐free metal halides have become the spotlight of the research on developing multifunctional optoelectronic materials as their properties show a wide range of tunability. However, most reported low dimensional metal halides only function in the ultra‐violet to visible range due to their large bandgap. Moreover, the organic cation based low dimensional metal halides show limited thermal stability; on the other hand, their inorganic cation based counterparts suffer from limited solution processability. A hybrid cation approach is proposed, where a zero dimensional (0D) metal halide ((DFPD)2CsBiI6) is developed by using mixed organic–inorganic cations: 4, 4‐difluoropiperidine (DFPD) and cesium (Cs+). This ensures both thermal stability and solution processability. Furthermore, [BiI6]3− octahedra are serving as active light absorption units, which ensures the bandgap to be located at the visible region. Its photoluminescence (PL) is further shifted to the near infrared (NIR) region by doping (DFPD)2CsBiI6 with antimony (Sb3+). The developed materials show multifunctional properties: thermochromic behavior, light detection, and NIR light emitting. This study expands the scope of developing multifunctional 0D metal halides.

Exciton Formation Dynamics and Band‐Like Free Charge‐Carrier Transport in 2D Metal Halide Perovskite Semiconductors

AbstractMetal halide perovskite (MHP) semiconductors have driven a revolution in optoelectronic technologies over the last decade, in particular for high‐efficiency photovoltaic applications. Low‐dimensional MHPs presenting electronic confinement have promising additional prospects in light emission and quantum technologies. However, the optimisation of such applications requires a comprehensive understanding of the nature of charge carriers and their transport mechanisms. This study employs a combination of ultrafast optical and terahertz spectroscopy to investigate phonon energies, charge‐carrier mobilities, and exciton formation in 2D (PEA)2PbI4 and (BA)2PbI4 (where PEA is phenylethylammonium and BA is butylammonium). Temperature‐dependent measurements of free charge‐carrier mobilities reveal band transport in these strongly confined semiconductors, with surprisingly high in‐plane mobilities. Enhanced charge‐phonon coupling is shown to reduce charge‐carrier mobilities in (BA)2PbI4 with respect to (PEA)2PbI4. Exciton and free charge‐carrier dynamics are disentangled by simultaneous monitoring of transient absorption and THz photoconductivity. A sustained free charge‐carrier population is observed, surpassing the Saha equation predictions even at low temperature. These findings provide new insights into the temperature‐dependent interplay of exciton and free‐carrier populations in 2D MHPs. Furthermore, such sustained free charge‐carrier population and high mobilities demonstrate the potential of these semiconductors for applications such as solar cells, transistors, and electrically driven light sources.

Modified luminescent properties from green afterglow to efficient orange emission in zirconium-based organometallic chloride scintillator by Sb3+ doping

Zero-dimension (0D) metal halides based on metals with the 5s2 lone pair have attracted great attentions due to their strong triplet broadband emission. However, the conversion from weak afterglow to efficient and fast photoluminescence by regulating the composition of 0D metal halides is still a tough challenge. Herein, Sb3+ ions-doped 0D (Ph4P)2ZrCl6·4CH3CN metal halides were synthesized by a simple solution crystallization method. Compared with the weak triplet green 560 nm afterglow from the organic Ph4P+ components, the emission of the Sb3+-doped material exhibits a strong orange photoluminescence at 660 nm with a high photoluminescence quantum yield of 72% by a host to dopant energy transfer process. In addition, a flexible large-sized X-ray scintillator screen with an area of 16 cm2 was prepared using polydimethylsiloxane as the host matrix, which exhibits excellent scintillation properties with light yields of 8,290 photons/MeV, low detectable limits of 0.986 μGy/s, and a near-infrared broadband emission from 600 nm to 850 nm under steady-state X-ray excitation, which is highly compatible with the response range of the long-wave sensitive silicon-based photodetectors. Therefore, this work not only provides a deep insight into the energy transfer process in the 0D metal halide materials but also opens an alternative approach to realize flexible large-size near-infrared X-ray imaging based on the 0D metal halide scintillator.

Multi‐Responsive 0D Organic–Inorganic Hybrid Cuprous Bromides Constructed via Ultra‐Facile Approaches for Multimodal Luminescent Anti‐Counterfeiting

AbstractLuminescent anti‐counterfeiting has the advantages of high secrecy, low cost, flexible design, simple operation, and convenient light‐regulation of luminescent materials, which makes it easy to achieve high‐level multimodal anti‐counterfeiting. Here, zero‐dimensional (0D) organic–inorganic hybrid luminescent crystals (TPA)CuBr2 (TPA+ = [N(CH2CH2CH3)4]+) with multiple responses to ultraviolet (UV) light, water, and thermal stimulus are synthesized through an ultra‐facile approach for multimodal luminescent anti‐counterfeiting. Water‐sensitive (TPA)CuBr2 could transform into 0D (TPA)2Cu4Br6 upon external water stimulus, accompanied by the change of luminescence color from cyan to orange under UV light irradiation. Both (TPA)CuBr2 and (TPA)2Cu4Br6 exhibit high photoluminescence quantum yields, and long photoluminescence decay lifetimes. In addition, (TPA)CuBr2 and (TPA)2Cu4Br6 show reversible “on‐off” luminescence phenomena and excellent cycling stability under thermal stimulus. Exhilaratingly, multimodal anti‐counterfeiting luminescent labels with high‐security level could be fabricated based on the multiple responsive organic–inorganic hybrid cuprous bromides. Moreover, the test paper based on (TPA)CuBr2 could be fabricated for the detection of trace water in isopropanol. This work demonstrates the capabilities of (TPA)CuBr2 and (TPA)2Cu4Br6 as high‐security anti‐counterfeiting materials and luminescent sensors, which provides an important reference for exploring 0D metal halides for high‐level luminescent anti‐counterfeiting.

Remarkable luminescence regulation covering full visible wavelength range of zero-dimensional indium-based metal halides

Recently, there has been a lot of research into the use of zero-dimensional (0D) metal halides as new luminous materials. However, the wide-range tunability of luminescence properties by structural engineering need to be explored. Here, we report the vacuum solid-state reaction synthesis of a series of indium-based A3InX6 (A = K, Rb, or Cs; X = Cl, Br, or their mixture) 0D metal halide single crystals (SCs). Alkali metal substitution at A site leads to similar luminescence properties but very different stability, among which Rb3InCl6 was the most air stable. Halogen alloying at the X site of Rb3InX6 can produce a luminescence wavelength modulation from 436 to 505 nm. The luminescence wavelength was further extended by Sb3+ doping to the 509–622 nm region. Finally, due to the high luminescence tunability covering the full visible wavelength range, we achieved pure white light-emitting diodes utilizing a combination of Rb3InBr2Cl4 and Rb3InBr2Cl4:Sb3+ SCs. This work provides a strategy with simultaneous substitution, alloying, and doping to modulate the luminescence properties of 0D lead-free metal halides for a variety of applications.

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2 O Vapor Sorption.

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with PbII in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)2 Pb5 Br14 . The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H2 O and D2 O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H2 O and D2 O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2O Vapor Sorption

AbstractIn this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure‐directing agents and counter‐cations. Reaction of the [2.2.2] cryptand (DHS) linker with PbII in acidic media gave rise to the first porous and water‐stable 2D metal halide semiconductor (DHS)2Pb5Br14. The corresponding material is stable in water for a year, while gas and vapor‐sorption studies revealed that it can selectively and reversibly adsorb H2O and D2O at room temperature (RT). Solid‐state NMR measurements and DFT calculations verified the incorporation of H2O and D2O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half‐maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid‐state batteries) for this class of hybrid semiconductors.

Facile and Effective Band Gap Engineering of 2D Ruddlesden–Popper Perovskites with Improved Structural and Optoelectronic Properties

Incorporation of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) into 3D metal-halide perovskite crystal structures has resulted in improved crystallinity and film morphology, reduced trap density, and enhanced charge carrier transport. However, due to intrinsic structural instability associated with 3D perovskites, their alkali metal ion-doped semiconductors are not a suitable option for real device optoelectronics. In recent years, Ruddlesden–Popper (RP)-phase quasi-two-dimensional (2D) metal halide perovskites have drawn considerable attention due to their tunable energy band gap, large electron and hole diffusion lengths (∼10 μm), and lower recombination rates compared to pristine 2D metal halide perovskites (n = 1). However, alkali metal ion-incorporated RP perovskite systems are not explored much; therefore, we demonstrate the incorporation of Rb+, using the RbI precursor, into the quasi-2D RP perovskite (BA)2(MA)Pb2Br7 (BA = C4H9NH3; MA = CH3NH3), which has also resulted in the successive replacement of Br– with I– in the PbBr6 network. Subsequent replacement of Br– with I– finely tuned the energy band gap from 2.92 to 2.43 eV, while keeping the phase of the pristine lead bromide RP perovskite intact, as confirmed by X-ray diffraction investigations. MA+ cations available at the outer edge sites got partially exchanged with Rb ions, which in turn has regulated the perovskite crystal growth, whereas the excess Rb+ alloyed with replaced Br– to form RbBr, which resulted in the formation of thinner grain boundaries and thus showed improved charge transport. Transient photocurrent measurements performed for RbI-doped perovskites (lateral configuration photodetector: fluorine-doped tin oxide (FTO)/RP-perovskite/FTO of channel width ∼150 μm), for 35 cycles under standard Xe-lamp (100 mW/cm2) illumination, have shown strong and fast photocurrent response with large photoresponsivity (3.92 × 10–4 A/W). Comparison of structural, optical, and optoelectronic properties of RbI-doped RP perovskites is carried out with the mixed RP perovskites and has further confirmed that Rb+ incorporation plays an important role in enhancing the crystal growth.

Anharmonic Exciton‐Phonon Coupling in Metal‐Organic Chalcogenides Hybrid Quantum Wells

AbstractIn contrast to inorganic quantum wells, hybrid quantum wells (HQWs) based on metal‐organic semiconductors are characterized by relatively soft lattices, in which excitonic states can strongly couple to lattice phonons. Therefore, understanding the lattice's impact on exciton dynamics is essential for harnessing the optoelectronic potential of HQWs. Beyond 2D metal halide perovskites, layered metal‐organic chalcogenides (MOCs), which are an air‐stable, underexplored material class hosting room‐temperature excitons, can be exploited as photodetectors, light emitting devices, and ultrafast photoswitches. Here, the role of phonons in the optical transitions of the prototypical MOC [AgSePh]∞ is elucidated. Impulsive stimulated Raman scattering (ISRS) allows the detection of coherent exciton oscillations driven by Fröhlich interaction with low‐energy optical phonons. Steady state absorption and Raman spectroscopies reveal a strong exciton‐phonon coupling (Huang‐Rhys parameter ≈1.7) and its anharmonicity, manifested as a nontrivial temperature‐dependent Stokes shift. The ab initio calculations support these observations, hinting at an anharmonic behavior of the low‐energy phonons <200 cm−1. These results untangle complex exciton‐phonon interactions in MOCs, establishing an ideal testbed for room‐temperature many‐body phenomena.

Crystal Growth, Structural and Electronic Characterizations of Zero-Dimensional Metal Halide (TEP)InBr4 Single Crystals for X-Ray Detection.

Recently, metal halides have shown great potential for applications such as solar energy harvesting, light emission, and ionizing radiation detection. In this work, we report the preparation, structural, thermal, and electronic properties of a new zero-dimensional (0D) halide (TEP)InBr4 (where TEP is tetraethylphosphonium organic cation, C8H20P+). (TEP)InBr4 single crystals are obtained within a few days of continuous crystal growth time via a solution growth methodology. (TEP)InBr4 shows a relatively large optical bandgap energy of 4.32 eV and a low thermal conductivity between 0.33±0.05 and 0.45±0.07 W/m-K. Based on the density functional theory (DFT) calculations, the highest occupied molecular orbitals (HOMOs) of (TEP)InBr4 are dominated by the Br states, while the lowest unoccupied molecular orbitals (LUMOs) are constituted by both In and Br states. (TEP)InBr4 single crystals exhibit a semiconductor resistivity of 1.73×1013 Ω·cm and a mobility-lifetime (mu-tau) product of 2.07×10-5 cm2/V. Finally, a prototype (TEP)InBr4 single crystal-based X-ray detector with a detection sensitivity of 569.85 uCGy-1cm-2 (at electrical field E=100 V/mm) was fabricated, indicating the potential use of (TEP)InBr4 for radiation detection applications.

Stepwise Crystalline Structural Transformation in 0D Hybrid Antimony Halides with Triplet Turn-on and Color-Adjustable Luminescence Switching.

Intelligent stimuli-responsive fluorescence materials are extremely pivotal for fabricating luminescent turn-on switching in solid-state photonic integration technology, but it remains a challenging objective for typical 3-dimensional (3D) perovskite nanocrystals. Herein, by fine-tuning the accumulation modes of metal halide components to dynamically control the carrier characteristics, a novel triple-mode photoluminescence (PL) switching was realized in 0D metal halide through stepwise single-crystal to single-crystal (SC-SC) transformation. Specifically, a family of 0D hybrid antimony halides was designed to exhibit three distinct types of PL performance including nonluminescent [Ph3EtP]2Sb2Cl8 (1), yellow-emissive [Ph3EtP]2SbCl5·EtOH (2), and red-emissive [Ph3EtP]2SbCl5 (3). Upon stimulus of ethanol, 1 was successfully converted to 2 through SC-SC transformation with enhanced PL quantum yield from ~0% to 91.50% acting as "turn-on" luminescent switching. Meanwhile, reversible SC-SC and luminescence transformation between 2 and 3 can be also achieved in the ethanol impregnation-heating process as luminescence vapochromism switching. As a consequence, a new triple-model turn-on and color-adjustable luminescent switching of off-onI-onII was realized in 0D hybrid halides. Simultaneously, wide advanced applications were also achieved in anti-counterfeiting, information security, and optical logic gates. This novel photon engineering strategy is expected to deepen the understanding of dynamic PL switching mechanism and guide development of new smart luminescence materials in cutting-edge optical switchable device.