Integrated Afterglow and Self-Trapped Exciton Emissions in Hybrid Metal Halides for Anti-Counterfeiting Applications

Optical activity levels of metal centers controlling multi-mode emissions in low-dimensional hybrid metal halides for anti-counterfeiting and information encryption

In-depth insight into the electronic competition principles between inorganic units and organic ligands proves to be extremely challenging for controlling multi-mode emissions in low-dimensional hybrid metal halides (LHMHs). Herein, an efficient blue emission from organic ligand was engineered in (DppyH)2MCl4 (Dppy = diphenyl-2-pyridylphosphine, M = Zn2+, Cd2+) due to the reverse type I band alignment constructed by optically inert units with nd10 shell electrons. By contrast, the optically active [MnCl4]2- with semi-fully filled 3d5 shell electrons prompts the band alignment of type II, resulting in the narrowband green emission of Mn2+, along with an energy transfer from DppyH+ to [MnCl4]2-. Beyond that, the band alignment of (DppyH)SbCl4 is further reversed to type I due to the strong stereochemical activity of 5s2 lone-pair electrons, resulting in the triplet-state (3P1 → 1S0) self-trapped exciton (STE) emission of [SbCl4]-. The conclusion is that the electronic configurations of metal centers govern the optical activity levels of inorganic units, which in turn controls the multi-mode emissions by maneuvering the band alignments. This research provides an enlightening perspective on the multi-mode emissions with tunable photoluminescence and resulting electronic transitions of LHMHs, whose derived emitters can be employed in anti-counterfeiting and information encryption.

Strategic engineering of cationic systems for spatial & temporal anti-counterfeiting applications in zero-dimensional Mn(II) halides

While spatial and time-resolved anti-counterfeiting technologies have gained increasing attention owing to their excellent tunable photoluminescence, achieving high-security-level anti-counterfeiting remains a challenge. Herein, we developed a spatial-time-dual-resolved anti-counterfeiting system using zero-dimensional (0D) organic-inorganic Mn(II) metal halides: (EMMZ)2MnBr4 (named M-1, EMMZ=1-Ethyl-3-Methylimidazolium Bromide) and (EDMMZ)2MnBr4 (named M-2, EDMMZ=1-Ethyl-2,3-Dimethylimidazolium Bromide). M-1 shows a bright green emission with a quantum yield of 78 %. It undergoes a phase transformation from the crystalline to molten state with phosphorescence quenching at 350 K. Reversible phase and luminescent conversion was observed after cooling down for 15 s. Notably, M-2 exhibits green light emission similar to M-1 but undergoes phase conversion and phosphorescence quenching at 390 K, with reversible conversion observed after cooling down for 5 s. The photoluminescence switching mode of on(green)-off-on(green) can be achieved by temperature control, demonstrating excellent performance with short response times and ultra-high cyclic reversibility. By leveraging the different quenching temperatures and reversible PL conversion times of M-1 and M-2, we propose a spatial-time-dual-resolved photoluminescence (PL) switching system that combines M-1 and M-2. This system enables multi-fold tuning of the PL switch for encryption and decryption through cationic engineering strategies by modulating temperature and cooling time. This work presents a novel and feasible design strategy for advanced-level anti-counterfeiting technology based on a spatial-time-dual-resolved system.

Realizing Stable Luminescence in Antimony Doped Hybrid Tin(IV) Chloride toward Full Spectrum WLED and Anticounterfeiting Applications

The outstanding optical properties empower Sb3+-doped zero-dimensional hybrid metal halides as cutting-edge luminescent materials. In this research, we present an efficient hybrid tin chloride, TEA2SnCl6:Sb3+ (TEA = tetraethylammonium), with broad dual emission bands peaking in the blue and orange regions that arise from the singlet and triplet state emissions of [SbCl5]2-, respectively. TEA2SnCl6:Sb3+ demonstrates a high photoluminescence quantum yield (PLQY) of 83.5% under 328 nm excitation, while 358 nm light induces an orange emission with a PLQY of 92.5% and a low thermal quenching behavior (73.9% at 423 K). Benefiting from the appealing luminescence properties of TEA2SnCl6:Sb3+, a full spectrum white light-emitting diode (WLED) device and an anticounterfeiting model were constructed, affirming the potential use of Sb3+-doped TEA2SnCl6 hybrid metal halide in versatile application fields.

N2H4Zn(HC3N3O3): exceptionally strong second harmonic generation and ultra-long phosphorescence

The discovery and designed synthesis of multifunctional materials is a leading pursuit in materials science. Herein, we report a novel hydro-isocyanurate, N2H4Zn(HC3N3O3), which combines strong second harmonic generation (SHG) and ultra-long room-temperature phosphorescence (RTP). The SHG intensity is the highest within the cyanurate system (13 × KDP), and RTP lifetime extends up to 448 ms, accompanied by a long-lasting afterglow visible to the naked eye for 1.2 s, surpassing most of the current metal-organic complexes. This advancement holds promise for the development of multifunctional optoelectronic devices, particularly leveraging second-harmonic generation (SHG) processes.

Flexible transparent and hydrophobic SiNCs/PDMS coatings for anti-counterfeiting applications

Silicon nanocrystals (SiNCs) have attracted considerable attention in many advanced applications due to silicon's high natural abundance, low toxicity, and impressive optical properties. However, little attention has been paid to fluorescence anti-counterfeiting applications based on lipophilic silicon nanocrystals. Moreover, it is also a challenge to fabricate aging-resistant anti-counterfeiting coatings based on silicon nanocrystals. Herein, this paper presents a demonstration of aging-resistant fluorescent anti-counterfeiting coatings based on red fluorescent silicon nanocrystals. In this work, lipophilic silicon nanocrystals (De-SiNCs) with red fluorescence were prepared first by thermal hydrosilylation between hydrogen-terminated silicon nanocrystals (H-SiNCs) and 1-decene. Subsequently, a new SiNCs/PDMS coating (De-SiNCs/DV) was fabricated by dispersing De-SiNCs into reinforcing PDMS composites with vinyl-capped silicone resin. Interestingly, the De-SiNCs/DV composites exhibit superior transparency (up to 85%) in the visible light range, outstanding fluorescence stabilities with an average lifetime of 20.59 μs under various conditions including acidic/alkaline environments, different organic solvents, high-humidity environments and UV irradiation. Meanwhile, the encapsulation of De-SiNCs is beneficial to enhancing the mechanical properties and thermal stability of De-SiNCs/DV composites. Additionally, the De-SiNCs/DV coating exhibits an excellent anti-counterfeiting effect on cotton fabrics when used as an ink in screen-printing. These findings pave the way for developing innovative flexible multifunctional anti-counterfeiting coatings in the future.

A Luminescent Hybrid Bimetallic Halide Family with Solvent-Coordinated Rare Earth and Alkaline Earth Metals

Hybrid metal halides are an extraordinary class of optoelectronic materials with extensive applications. To further diversify and study the in-depth structure-property relations, we report here a new family of 21 zero-dimensional hybrid bimetallic chlorides with the general formula A(L)n[BClm] (A=rare earth (RE), alkaline earth metals and Mn; L=solvent ligand; and B=Sb, Bi and Te). The RE(DMSO)8[BCl6] (RE=La, Ce, Sm, Eu, Tb, and Dy; DMSO=dimethyl sulfoxide) series shows broadband emission attributed to triplet radiative recombination from Sb and Bi, incorporating the characteristic emission of RE metals, where Eu(DMSO)8[BiCl6] shows a staggering PL quantum yield of 94 %. The pseudo-octahedral [SbCl5] with Cl vacancy in AII(DMSO)6[SbCl5] (AII=Mg, Ca and Mn) and the square pyramidal [SbCl5] in AII(TMSO)6[SbCl5] (TMSO=tetramethylene sulfoxide) enhance the stereoactive expression of the 5 s2 lone pairs of Sb3+, giving rise to the observation of dual-band emission of singlet and triplet emission, respectively. A series of Te(IV) analogues have been characterized, showing blue-light-excitable single-band emission. This work expands the materials space for hybrid bimetallic halides with an emphasis on harnessing the RE elements, and provides important insights into designing new emitters and regulating their properties.

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.

Host-Guest Metal-Organic Frameworks-Based Long-Afterglow Luminescence Materials

Long-afterglow materials have a broad of applications in optoelectronic devices, sensors, medicine and other fields due to their excellent luminescent properties. The host-guest long-afterglow MOFs material combines the advantages of multi-component characteristics and the stability of MOFs, which improves its luminous performance and expands its other properties. This review introduces the classification, synthesis and application of host-guest MOFs materials with long afterglow. Due to their rigid frames and multi-channel characteristics, MOFs can load common guest materials including rare earth metals, organic dyes, carbon dots, etc. The synthesis methods of loading guest materials into MOFs include solvothermal synthesis, post-encapsulation, post-modification, etc. Those long-afterglow host-guest MOFs have a wide range of applications in the fields of sensors, information security and biological imaging.

Blue Long Afterglow and Ultra Broadband Vis-NIR Emission from All-Inorganic Copper-Doped Silver Halide Single Crystals

All-inorganic metal halides with afterglow emission have attracted increasing attention due to their significantly longer afterglow duration and higher stability compared to their organic-inorganic hybrid counterparts. However, their afterglow colors have not yet reached the blue spectral region. Here, we report all-inorganic copper-doped Rb2AgBr3 single crystals with ultralong blue afterglow (>300 s) by modulating defect states through doping engineering. The introduction of copper(I) ions into Rb2AgBr3 facilitates the formation of bromine vacancies, thus increasing the density of trap states available for charge storage and enabling bright, persistent emission after ceasing the excitation. Moreover, cascade energy transfer between distinct emissive centers in the crystals results in ultra-broadband photoluminescence, not only covering the whole white light with near-unity quantum yield but also extending into the near-infrared region. This 'cocktail' of exotic light-emission properties, in conjunction with the excellent stability of copper-doped Rb2AgBr3 crystals, allowed us to demonstrate their implementation to solid-state lighting, night vision, and intelligent anti-counterfeiting.

High External Quantum Efficiency and Dual-Band Emission of (C7H18N)3Sb2Cl9 for Sensitivity Temperature Sensing

Organic-inorganic hybrid halides have gained attention for their ease of processing and remarkable optoelectronic properties. However, the relationship between the structure and optical properties requires further exploration. In this study, the butyltrimethylammonium cation (C7H18N+) was chosen, and seven compounds were synthesized: (C7H18N)3Sb2X9 (X = Cl, Br), (C7H18N)3Bi2X9 (X = Cl, Br, I), and (C7H18N)(C2H8N)MBr5 (M = Sb, Bi). Crystals with a single organic cation exhibit a zero-dimensional structure, while the introduction of dimethylamine ions increases the crystal dimensionality from zero-dimensional (C7H18N)3Sb2Br9 to one-dimensional (C7H18N)(C2H8N)SbBr5. Under 372 nm excitation, (C7H18N)3Sb2Cl9 showed broad orange-red single-band emission with a high photoluminescence quantum yield of 88.4% and an external quantum efficiency of up to 56.9%. A white light-emitting diode based on (C7H18N)3Sb2Cl9 achieved a high color rendering index of 96.3. Moreover, dual-band emission was observed in (C7H18N)3Sb2Cl9 under 308 nm excitation, which exhibits an absolute temperature sensitivity of 1.96 × 10-3 K-1 (320 K), and a flexible film was prepared by incorporating polydimethylsiloxane. This shows the promise of hybrid metal halides as photoluminescent materials and their possibilities for temperature sensing.

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.

Solid-State Photochemical Cascade Process Boosting Smart Ultralong Room-Temperature Phosphorescence in Bismuth Halides

Molecular ultralong room-temperature phosphorescence (RTP), exhibiting multiple stimuli-responsive characteristics, has garnered considerable attention due to its potential applications in light-emitting devices, sensors, and information safety. This work proposes the utilization of photochemical cascade processes (PCCPs) in molecular crystals to design a stepwise smart RTP switch. By harnessing the sequential dynamics of photo-burst movement (induced by [2+2] photocycloaddition) and photochromism (induced by photogenerated radicals) in a bismuth (Bi)-based metal-organic halide (MOH), a continuous and photo-responsive ultralong RTP can be achieved. Furthermore, utilizing the same Bi-based MOH, diverse application demonstrations, such as multi-mode anti-counterfeiting and information encryption, can be easily implemented. This work thus not only serves as a proof-of-concept for the development of solid-state PCCPs that integrate photosalient effect and photochromism with light-chemical-mechanical energy conversion, but also lays the groundwork for designing new Bi-based MOHs with dynamically responsive ultralong RTP.

Multisite Fine-Tuning in Hybrid Cadmium Halides Enables Wide Range Emissions for Anti-Counterfeiting

Achieving tunable emissions spanning the spectrum, from blue to near-infrared (NIR) light, within a single component is a formidable challenge with significant implication, particularly in tailoring multicolor luminescence for anti-counterfeiting purposes. In this study, we demonstrate a broad spectrum of emissions, covering blue to red and extending into NIR light in [BPy]2CdX4 : xSb3+ (BPy=Butylpyridinium; X=Cl, Br; x=0 to 0.08) through precise multisite structural fine-tuning. Notably, the multicolor emissions from [BPy]2CdBr4 : Sb3+ manifest a distinctive pattern, transitioning from blue to yellow in tandem with the host [BPy]2CdBr4 and further extending from yellow to NIR with its homologous [BPy]2CdCl4 : Sb3+, resulting in the simultaneous presence of intersecting and independent emission colors. Detailed modulation of chemical composition enables partial luminescence switching, facilitating the creation of diverse patterns with multicolor luminescence by employing [BPy]2CdX4 : xSb3+ as phosphors. This study for the first time successfully implements several groups of tunable emission colors in a single matrix via multisite fine-tuning. Such an effective strategy not only develops the specific relationships between tunable emissions and adjustable compositions, but also introduces a cost-effective and straightforward approach to achieving unique, high-level, plentiful-color and multiple-information-storage labels for advanced anti-counterfeiting applications.

Polymeric Metal Halides with Bright Luminescence and Versatile Processability

Most of current metal halide materials, including all inorganic and organic-inorganic hybrids, are crystalline materials with poor workability and plasticity that limit their application scope. Here, we develop a novel class of materials termed polymeric metal halides (PMHs) through introducing polycations into antimony-based metal halide materials as A-site cations. A series of PMHs with orange-yellow broadband emission and large Stokes shift originating from inorganic self-trapped excitons are successfully prepared, which meanwhile exhibit the excellent processability and formability of polymers. The versatility of these PMHs is manifested as the broad choices of polycations, the ready extension to manganese- and copper-based halides, and the tolerance to molar ratios between polycations and metal halides in the formation of PMHs. The merger of polymer chemistry and inorganic chemistry thus provides a novel generic platform for the development of metal halide functional materials.

Mn(II)-Activated Zero-Dimensional Zinc(II)-Based Metal Halide Hybrids with Near-Unity Photoluminescence Quantum Yield

As derivatives of metal halide perovskite materials, low-dimensional metal halide materials have become important materials that have attracted much attention in recent years. As one branch, zinc-based metal halides have the potential for practical applications due to their lead-free, low-toxicity and high-stability characteristics. However, pure zinc-based metal halide materials are still limited by their poor optical properties and cannot achieve large-scale practical applications. Therefore, in this work, we report an organic-inorganic hybrid zero-dimensional zinc bromide, (TDMP)ZnBr4, using transition metal Mn2+ ions as dopants and incorporating them into the (TDMP)ZnBr4 lattice. The original non-emissive (TDMP)ZnBr4 exhibits bright green emission under the excitation of external UV light after the introduction of Mn2+ ions with a PL peak position located at 538 nm and a PLQY of up to 91.2%. Through the characterization of relevant photophysical properties and the results of theoretical calculations, we confirm that this green emission in Mn2+:(TDMP)ZnBr4 originates from the 4T1 → 6A1 optical transition process of Mn2+ ions in the lattice structure, and the near-unity PLQY benefits from highly localized electrons generated by the unique zero-dimensional structure of the host material (TDMP)ZnBr4. This work provides theoretical guidance and reference for expanding the family of zinc-based metal halide materials and improving and controlling their optical properties through ion doping.

Zero-Dimensional Tellurium-Based Organic-Inorganic Hybrid Halide Single Crystal with Yellow-Orange Emission from Self-Trapped Excitons

Organic-inorganic hybrid halides and their analogs that exhibit efficient broadband emission from self-trapped excitons (STEs) offers an unique pathway towards realization of highly efficient white light sources for lighting applications. An appropriate dilution of ns2 ions into a halide host is essential to produce auxiliary emissions. However, the realization of ns2 cation-based halides phosphor that can be excited by blue light-emitting diode (LED) is still rarely reported. In this study, a zero-dimensional Te-based single crystal (C8H20N)2TeCl6 was synthesized, which exhibits a yellow-orange emission centered at 600 nm with a full width at half maximum of 130 nm upon excitation under 437 nm. Intense electron-phonon coupling was confirmed in the (C8H20N)2TeCl6 single crystal and the light emitting mechanism is comprehensively discussed. The results of this study are pertinent to the emissive mechanism of Te-based hybrid halides and can facilitate discovery of unidentified metal halides with broadband excitation features.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

Pseudo-2D Layered Organic-Inorganic Manganese Bromide with a Near-Unity Photoluminescence Quantum Yield for White Light-Emitting Diode and X-Ray Scintillator

Eco-friendly lead-free organic-inorganic manganese halides (OIMHs) have attracted considerable attention in various optoelectronic applications because of their superior optical properties and flexible solution processibility. Herein, we report a novel pseudo-2D layered OIMH (MTP)2 MnBr4 (MTP: methyltriphenylphosphonium), which exhibits intense green emission under UV/blue or X-ray excitation, with a near-unity photoluminescence quantum yield, high resistance to thermal quenching (I150 °C =84.1 %) and good photochemical stability. These features enable (MTP)2 MnBr4 as an efficient green phosphor for blue-converted white light-emitting diodes, demonstrating a commercial-level luminous efficiency of 101 lm W-1 and a wide color gamut of 116 % NTSC. Moreover, these (MTP)2 MnBr4 crystals showcase outstanding X-ray scintillation properties, delivering a light yield of 67000 photon MeV-1 , a detection limit of 82.4 nGy s-1 , and a competitive spatial resolution of 6.2 lp mm-1 for X-ray imaging. This work presents a new avenue for the exploration of eco-friendly luminescent OIMHs towards multifunctional light-emitting applications.

0D hybrid indium halide as a highly efficient X-ray scintillation and ultra-sensitive fluorescent probe

Halide perovskite nanocrystal (PNC) of 3D CsPbX3 as a scintillator has aroused intensive attention with advanced applications in radiation detection and X-ray imaging. However, the low light yield and serious toxicity of Pb2+ severely hinder advanced optoelectronic applications. To reduce these fatal shortcomings, a family of new environmentally friendly 0D hybrid lead-free indium halides of [DADPA]InX6·H2O (DADPA = 3,3'-diaminodipropylamine; X = Cl and Br) was prepared. Upon UV excitation, these halides display strong broadband yellow-orange light emissions, and the photoluminescence quantum yield (PLQY) can be optimized up to near unity through the Sb3+-doping strategy. Significantly, high PLQY, negligible self-absorption and low attenuation ability toward X-ray render extraordinary scintillation performance with a high light yield of 51 875 photons MeV-1 and ultralow detection limit of 98.3 nGyair s-1, which is far superior to typical 3D PNC scintillators. Additionally, the ultra-high spatial resolution of 25.15 lp mm-1, negligible afterglow time (2.75 ms) and robust radiant stability demonstrates excellent X-ray imaging performance. To the best of our knowledge, this is the first report on X-ray scintillation based on 0D indium halide materials.

Ultralow-loss Optical Waveguides through Balancing Deep-Blue TADF and Orange Room Temperature Phosphorescence in Hybrid Antimony Halide Microstructures

Harnessing the potential of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is crucial for developing light-emitting diodes (LEDs), lasers, sensors, and many others. However, effective strategies in this domain are still relatively scarce. This study presents a new approach to achieving highly efficient deep-blue TADF (with a PLQY of 25 %) and low-energy orange RTP (with a PLQY of 90 %) through the fabrication of lead-free hybrid halides. This new class of monomeric and dimeric 0D antimony halides can be facilely synthesized using a bottom-up solution process, requiring only a few seconds to minutes, which offer exceptional stability and nontoxicity. By leveraging the highly adaptable molecular arrangement and crystal packing modes, the hybrid antimony halides demonstrate the ability to self-assemble into regular 1D microrod and 2D microplate morphologies. This self-assembly is facilitated by multiple non-covalent interactions between the inorganic cores and organic shells. Notably, these microstructures exhibit outstanding polarized luminescence and function as low-dimensional optical waveguides with remarkably low optical-loss coefficients. Therefore, this work not only presents a pioneering demonstration of deep-blue TADF in hybrid antimony halides, but also introduces 1D and 2D micro/nanostructures that hold promising potential for applications in white LEDs and low-dimensional photonic systems.

Achieving Color-Tunable Long Persistent Luminescence in Cs2 CdCl4 Ruddlesden-Popper Phase Perovskites

Two-dimensional (2D)-halide perovskites have been enriched over recent years to offer remarkable features from diverse chemical structures and environmental stability endowed with exciting functionalities in photoelectric detectors and phosphorescence systems. However, the low conversion efficiency of singlet to triplet in 2D hybrid halide perovskites reduces phosphorescence lifetimes. In this study, the long persistent luminescence of 2D all-inorganic perovskites with a self-assembled 2D interlayer galleries structure is investigated. The results show that the decay time of the long persistent luminescence increases from 450 s to 600 s, and the luminescence color changes from cyan to orange, and the thermal stability of photoluminescence enhances dramatically after replacing Cd2+ by appropriate Mn2+ ions in 2D Cs2 CdCl4 Ruddlesden-Popper phase perovskites. Furthermore, diversified anti-counterfeiting modes are fabricated to highlight the promising applications of Cs2 CdCl4 perovskite systems with tunable persistent luminescence in advanced anti-counterfeiting. Therefore, our studies provide a novel model for realizing tunable long persistent luminescence of perovskite with 2D self-assembled layered structure for advanced anti-counterfeiting.

Tunable Afterglow and Self-Trapped Exciton Emissions in Zr (IV)-Based Organic-Inorganic Metal Halide Hybrids by Metal-Ion Doping

Low-dimensional hybrid metal halide (LDHMH) materials have attracted considerable attention owing to their intriguing optical properties. To the best of the knowledge, this is the first study to successfully demonstrate both self-trap exciton (STE) and afterglow emissions in Zr-based LDHMH materials. The obtained pure (Ph3 S)2 ZrCl6 crystals showed near-ultraviolet phosphorescence and a green afterglow owing to the organic cation Ph3 S+ , while the Bi-doped and Sb-doped crystals exhibited both STE and afterglow emissions. However, the Te-doped crystals showed only a broad yellow STE emission owing to the [TeCl6 ]2- octahedron. In addition, all the crystals showed good stability. Notably, Sb-doped crystals produced white light, which can be adjusted between cold white and warm white using different excitations. Finally, this strategy for both STE and afterglow emissions can be applied to other LDHMH materials for optical applications.

Photophysical studies for Cu(i)-based halides: broad excitation bands and highly efficient single-component warm white-light-emitting diodes

Designing and synthesizing cuprous halide phosphors unifying efficient low-energy emission and a broad excitation band is still a great challenge. Herein, by rational component design, three novel Cu(i)-based metal halides, DPCu₄X₆ [DP = (C₆H₁₀N₂)₄(H₂PO₂)₆; X = Cl, Br, I], were synthesized by reacting p-phenylenediamine with cuprous halide (CuX), and they show similar structures, consisting of isolated [Cu₄X₆]^2- units separated by organic layers. Photophysical studies uncover that the highly localized excitons and rigid environment give rise to highly efficient yellow-orange photoluminescence in all compounds with the excitation band spanning from 240 to 450 nm. The bright PL in DPCu₄X₆ (X = Cl, Br) originates from self-trapped excitons due to the strong electron-phonon coupling. Intriguingly, DPCu₄I₆ features a dual-band emissive characteristic, attributed to the synergistic effect of halide/metal-to-ligand charge-transfer (X/MLCT) and triplet cluster-centered (³CC) excited states. Benefiting from the broadband excitation, a high-performance white-light emitting diode (WLED) with a high color rendering index of 85.1 was achieved using single-component DPCu₄I₆ phosphor. This work not only unveils the role of halogens in the photophysical processes of cuprous halides, but also provides new design principles for high-performance single-component WLEDs.

Linear optical afterglow and nonlinear optical harmonic generation from chiral tin(IV) halides: the role of lattice distortions

The striking chemical variability of hybrid organic-inorganic metal halides (HOMHs) endows them with fascinating optoelectronic properties. The inorganic skeletons of HOMHs are often flexible and their lattice deformations could serve as an effective factor for enabling the functionalities of HOMHs. Here, the linear and nonlinear optical properties of zero-dimensional (0D) tin(IV) halides have been tuned by structural distortion facilitated by the chiral amines. Enantiopure α-methylbenzyl ammoniums (XMBA, X = Cl, F) effectively transfer their chirality to the inorganic scaffolds when forming the tin(IV) halides, which enables polar arrangements in their crystals and leads to outstanding second-order nonlinear optical performances. In contrast, the racemic mixture of R- and S-FMBA results in the formation of HOMHs with room temperature phosphorescence. The lower lattice deformation in (rac-FMBA)₂SnCl₆ restrains the non-radiative decay from electron-phonon coupling and facilitates the photoluminescence. Meanwhile, the marked π-π interaction stabilizes the T₁ state for phosphorescent emission. These distinct linear and nonlinear optical properties denote the important role that the lattice distortion plays in tuning the optical properties of low-dimensional HOMHs, and offer a promising perspective of 0D tin(IV) halides for applications in optoelectronic materials and devices.

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

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

Multimodal-Responsive Circularly Polarized Luminescence Security Materials

Nations, industries, and aspects of everyday life have undergone forgery and counterfeiting ever since the emergence of commercialization. Securing documents and products with anticounterfeit additives shows promise for authentication, allowing one to combat ever-increasing global counterfeiting. One most-used effective encryption strategy is to combine with optical-security markers on the required protection objects; however, state-of-the-art labels still suffer from imitation due to their poor complexity and easy forecasting, as a result of deterministic production. Developing advanced anticounterfeiting tags with unusual optical characters and further incorporating complex security features are desired to achieve multimodal, unbreakable authentication capacity; unfortunately, this has not yet been achieved. Here, we prepare a series of stable circularly polarized luminescence (CPL) materials, composed of toxicity-free, high-quality-emitting inorganic quantum dots (QDs) and liquid crystals, using a designed helical-coassembly strategy. This CPL system achieves a figure of merit (FM, assessing the performance of both luminescence dissymmetry and quantum yield) value of 0.39, fulfilling practical demands for anticounterfeiting applications. Based on these CPL structures, we produce a type of multimodal-responsive security materials (MRSMs) that exhibits six different stimuli-responsive modes, including light activation, polarization, temperature, voltage, pressure, and view angle. Thus, we show a proof-of-principle blockchain-like integrated anticounterfeiting system, allowing multimodal-responsive, interactive/changeable information encryption-decryption. We further encapsulate the obtained security materials into a fiber to expand our materials to work on flexible fabrics, that is, building an intelligent textile with a color-adaptable function along with environmental change.

Polaron states of the full-configuration defects in metal halide perovskites

The systematical analysis for varieties of defects with different depths and lattice relaxation strengths in metal halide perovskites (MHPs) is a challenging task. Here, we study the energy shifts of the full-configuration defects due to the polaron effect based on the all-coupling variational method in MHPs, where these polaron states are formed stemming from different defect species coupling with the longitudinal optical phonon modes via Fro¨hlich mechanism. We find that the polaron effect results in defect levels varying from tens to several hundreds of meV, which are very close to the correction of defect levels due to the defect-polaron effect, especially for these defects migration proved in the recent experiments in MHPs. These results provide the significant enlightenment not only for analyzing the radiation and non-radiation processes of carriers mediated by defects, but also for optimizing defect effect in the photovoltaic and photoelectric devices based on MHPs materials.

Sn(II)-doped one-dimensional hybrid metal halide [C5H14NO]CdCl3 single crystals with broadband greenish-yellow light emission

Low-dimensional organic-inorganic hybrid halides, as an important branch of metal halide materials, have attracted much attention due to their excellent photoelectric properties. Herein, we designed one new hybrid cadmium chloride [C₅H₁₄NO]CdCl₃ based on combinations of the d¹⁰ metal cation (Cd²⁺) and choline chloride molecules. [C₅H₁₄NO]CdCl₃ single crystals belong to the orthorhombic Pna2₁ space group and show a one-dimensional (1D) structure with distorted [CdCl₅O]^5- octahedra. The second harmonic generation (SHG) response of [C₅H₁₄NO]CdCl₃ exhibits an intensity of approximately 0.4 × KDP. Moreover, the photoluminescence properties of the [C₅H₁₄NO]CdCl₃ crystal are activated by doping with Sn²⁺ ions having stereochemically active lone pair 5s² electrons. Under UV excitation conditions, bright greenish-yellow light emission can be observed, and the quantum efficiency (PLQY) is as high as 91.27%. The luminescence mechanism is revealed by combining the results of temperature dependent luminescence and density functional theory (DFT) calculation. This work can serve as a guide for the design and synthesis of emerging optical materials.

Water-stable halide coordination polymers with dual self-trapped exciton emissions for dual-mode Hg2+ sensing

An acid- and base-stable halide coordination polymer exhibits excitation-dependent dual self-trapped exciton emissions and colorimetric and turn-off sensing on Hg2+ ions.

Self-trapped excitons in soft semiconductors

Self-trapped excitons (STEs) have attracted tremendous attention due to their intriguing properties and potential optoelectronic applications. STEs are formed from the lattice distortion induced by the strong electron (exciton)-phonon coupling in soft semiconductors upon photoexcitation, which features in broadband photoluminescence (PL) emission spectra with a large Stokes shift. Recently, significant progress has been achieved in this field but many remain challenges that need to be solved, including the understanding of the underlying physical mechanism, tuning of the performance, and device applications. Along these lines, for the first time, systematic experimental characterizations and advanced theoretical calculations are presented in this review to shed light on the physical mechanism. The possibility of tuning the STEs through multiple degrees of freedom is also presented, along with an overview of the STE-based emerged applications and future research perspectives.

Achieving Ultrahigh Efficiency Vacancy-Ordered Double Perovskite Microcrystals via Ionic Liquids

Lead-free perovskites have gained much interest for photovoltaic and optoelectronic applications. But instability and low quantum efficiency significantly limit their prospects for future applications. Here, a general route is reported to synthesize highly stable lead-free perovskites on a large scale with remarkably enhanced quantum efficiency. Two typical vacancy-ordered double perovskites (Cs₂ ZrCl₆ and Cs₂ SnCl₆ ) and their corresponding Bi³⁺ or Sb³⁺ doped samples are synthesized in ionic liquids (ILs) solutions via a simple solution method. These prepared perovskite samples all exhibit high-quality crystalline structures and their photoluminescence quantum yields (PLQYs) all show an increase close to 200% compared to the samples prepared in the hydrochloric acid system. The PLQY of Sb-doped Cs₂ ZrCl₆ with excellent thermal stability can reach up to 90.2%, which is the highest value reported for this system (Cs₂ ZrCl₆ :Sb). Density functional theory calculations reveal that the corresponding interaction between the ILs and the samples can effectively improve the crystal quality and reduce energy loss. The potential applications of the prepared samples for high-performance white light-emitting diodes and optical anti-counterfeiting are also demonstrated. The findings provide a straightforward way to obtain ultrahigh quantum efficiency vacancy-ordered double perovskites with good thermal stability and excellent optoelectronic properties.

Metal-Halide Coordination Polymers with Excitation Wavelength- and Time-Dependent Ultralong Room-Temperature Phosphorescence

Metal-organic hybrids with ultralong room-temperature phosphorescence (RTP) have potential applications in many fields, including optical communications, anticounterfeiting, encryption, bioimaging, and so on. Herein, we report two isostructural one-dimensional zinc-organic halides as coordination polymers ZnX₂(bpp) (X = Cl, 1; Br, 2; bpp = 1,3-di(4-pyridyl)propane) with excitation wavelength- and time-dependent ultralong RTP properties. The dynamic multicolor afterglow can be assigned to the emission of the pristine ligand bpp and its interactions with halogen atoms. Experiments and theoretical calculations both suggest that ZnX₂ is crucial for ultralong RTP: (a) the metal coordination and X...π bonds in coordination polymers fix the bpp molecules and suppress the nonradiative transitions; (b) the spin-orbital coupling of coordination polymers is largely enhanced relative to the bpp because of the heavy atom effect; and (c) the charge transfer exists between halogens and bpp ligand. Therefore, this work not only presents metal-halide coordination polymers with excitation wavelength- and time-dependent RTP properties, but also provides a facile method for the new types of dynamic multicolor afterglow materials.

Organic Cation-Directed Modulation of Emissions in Zero-Dimensional Hybrid Tin Bromides

Zero-dimensional hybrid metal halides (0D HMHs) are attractive due to their intriguing self-trapped exciton (STE) emission properties. However, the effect of organic cations on the emission of 0D HMHs is relatively underexplored. Herein, we report two types of 0D hybrid tin bromides, (BMe)₂SnBr₆ (BMe = C₈N₂H₁₈) and (MeH)₂SnBr₆ (MeH = C₇N₂H₁₆), which share similar structural features with different hydrogen bonding (HB) interactions between [SnBr₆]^4- anions and organic cations. The (BMe)₂SnBr₆ with weak HB interactions exhibits only STE emission, while the (MeH)₂SnBr₆ exhibits both STE and charge transfer exciton emissions owing to the strong HB interactions, resulting in an excitation-dependent emission at cryogenic conditions. Detailed structural analyses and Hirshfeld surface calculations confirm that the enhanced HB interactions are essential to obtain the multiple emissions in (MeH)₂SnBr₆.

Zero-Dimensional Zn-Based Halides with Ultra-Long Room-Temperature Phosphorescence for Time-Resolved Anti-Counterfeiting

Though fluorescence-tag-based anti-counterfeiting technology has distinguished itself with cost-effective features and huge information loading capacity, the clonable decryption process of spatial-resolved anti-counterfeiting cannot meet the requirements for high-security-level anti-counterfeiting. Herein, we demonstrate a spatial-time-dual-resolved anti-counterfeiting system based on new organic-inorganic hybrid halides BAPPZn₂ (Cl_y Br_1-y )₈ (BAPP=1,4-bis(3-ammoniopropyl)piperazinium, y=0-1) with ultra-long room-temperature phosphorescence (RTP). Remarkably, the afterglow lifetime can be facilely tuned by regulating the halide-induced heavy-atom effect and can be identified by the naked eyes or with the help of a simple machine vision system. Therefore, the short-lived unicolor fluorescence and lasting-time-tunable RTP provide the prerequisites for unicolor-time-resolved anti-counterfeiting, which lowers the decryption-device requirements and further provides the design strategy of advanced portable anti-counterfeiting technology.

Photoluminescent Properties of Two-Dimensional Manganese(II)-Based Perovskites with Different-Length Arylamine Cations

The participation of organic cations plays an important role in tuning broad-spectra emissions. Herein, we synthesized a series of Mn(II)-based two-dimensional (2D) halide perovskites with arylamine cations of different lengths having the general formula (C₆H₅(CH₂)_xNH₃)₂MnCl₄ (x = 1-4), with the x = 4 compound reported here for the first time. With the increase in the -(CH₂)- in organic cations, the distance between adjacent inorganic layers increases, causing the title compounds to exhibit different structural distortions. As the Mn-Cl-Mn angular distortion increases, the experimental optical band gaps of the title compounds increase correspondingly. When the angle distortion between the octahedrons of the compounds is similar, the band gaps may also be affected by the distortion of the octahedron itself (the bond-length distortion of 2 is greater than that of 4). Under UV-light irradiation at 298 K, all of the compounds exhibit two emission peaks centered at 480-505 and 610 nm, corresponding to the organic-cation emission and the ⁴T₁(G) to ⁶A₁(S) radiative transition of Mn²⁺ ions, respectively. Among these title compounds, (PPA)₂MnCl₄ [(PPA)⁺ = C₆H₅(CH₂)₃NH₃⁺] exhibits the strongest photoluminescence (PL). The study of the title compounds contributes to an in-depth understanding of the relationship between the structural distortion and optical properties of 2D Mn(II)-based perovskite materials.