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Metal halide perovskites (MHPs) have received considerable attention due to their intrinsically disordered structures, leading to abnormally low thermal conductivity, which is beneficial for energy harvesting applications. Compared with organic–inorganic hybrid MHPs, all inorganic MHPs exhibit better thermal stability, but thermal conductivity is relatively high, about twice that of hybrid MHPs. In this study, we investigate an all-inorganic vacancy-ordered double perovskite, Cs2SnI6, characterized by a cage-like structure with an octahedral interstitial radius of approximately 1.638 Å, allowing for the accommodation of various metal ions. We successfully introduced Mg2+ ions as guest fillers into the octahedral interstices of Cs2SnI6. The weak ionic bonds formed by Mg2+ in these oversized interstices induce vibrations that enhance atomic disorder and anharmonicity within the structure. As a result, we achieved an exceptionally low thermal conductivity of κ = 0.11 W m−1 K−1 at room temperature in Mg0.102Cs2SnI6, representing a 21% reduction compared to the undoped sample and marking one of the lowest values reported for MHPs. This research offers a novel approach to effectively regulate disorder and significantly reduce the thermal conductivity of all-inorganic MHPs. [ABSTRACT FROM AUTHOR]

Despite the overwhelming success of organic–inorganic metal halide perovskites in the field of energy harvesting, many of the aspects of these materials are not well understood even now. Specifically, the origin of multiple peaks emergence in photoluminescence (PL) spectra is widely debated. In the present work, emission spectra of mix halide perovskites, MAPb(Br1−xClx)3 (x = 0–1) on single crystal samples, have been investigated in detail. In addition to the band-to-band transition peak, two other peaks were observed. The amplitude of these two additional peaks appears to be strongly dependent on halide composition. Observed extra peaks in PL spectra were seen to be less pronounced in the pure end compositions (x = 0 and 1) and intense for intermediate compositions. It has been observed that multiple peaks seen in the bulk emission spectra are closely related to the coordination chemistry of a halide anion. X-ray absorption near edge spectroscopy indicated the existence of a different environment for the bromine anion, which might be responsible for the modification in the electronic structure with the change in halide composition. This modification in the electronic structure is suggested to be responsible for the appearance of debated multiple peak emissions in the PL spectra. These results are anticipated to pave the way for further research to enhance the understanding of the optoelectronic properties of mixed halide perovskites. [ABSTRACT FROM AUTHOR]

The stability of perovskite materials is profoundly influenced by the presence of moisture in the surrounding environment. While it is well-established that water triggers and accelerates the black–yellow phase transition, leading to the degradation of the photovoltaic properties of perovskites, the underlying microscopic mechanism remains elusive. In this study, we employ classical molecular dynamics simulations to examine the role of water molecules in the yellow–black phase transition in a typical inorganic metal halide perovskite, CsPbI3. We have demonstrated, through interfacial energy calculations and classical nucleation theory, that the phase transition necessitates a crystal–amorphous–crystal two-step pathway rather than the conventional crystal–crystal mechanism. Simulations for CsPbI3 nanowires show that water molecules in the air can enter the amorphous interface between the black and yellow regions. The phase transition rate markedly increases with the influx of interfacial water molecules, which enhance ion diffusivity by reducing the diffusion barrier, thereby expediting the yellow–black phase transition in CsPbI3. We propose a general mechanism through which solvent molecules can greatly facilitate phase transitions that otherwise have prohibitively high transition energies. [ABSTRACT FROM AUTHOR]

Metal halide perovskite materials (MHPs) are promising for several applications due to their exceptional properties. Understanding excitonic properties is essential for exploiting these materials. For this purpose, we focus on CsPbBr3 single crystals, which have higher crystal quality, are more stable, and have no Rashba effect at low temperatures compared to other 3D MHPs. We have estimated exciton energy positions, longitudinal-transverse splitting energy, and damping energy using low-temperature reflection spectra. Under high excitation intensity, two biexciton emissions (M-emission) and exciton–exciton scattering emission (P-emission) were observed. We assign the two M-emissions to the emission to the states of longitudinal and transverse excitons, i.e., ML and MT emissions. From the energy position of the MT emission, the biexciton binding energy has been estimated to be ∼2 meV. By analyzing P-emission obtained from the back side of the sample, we have estimated the exciton binding energy to be 17.8–23.7 meV. This estimation minimizes the influence of the wavenumber distribution in the scattering process. In addition, time-resolved transmittance measurements using pulsed white light have revealed the group velocity dispersion. Comparing experimental results with theoretical calculations using the Lorentz model clarifies that exciton dynamics in CsPbBr3 can be described with a simple Lorentz model. These insights enhance the understanding of exciton behavior and support the development of exciton-based devices using MHPs. [ABSTRACT FROM AUTHOR]

Zero-dimensional (0D) hybrid metal halides (HMHs) have emerged as a promising platform for exploring excitation-dependent multicolor luminescent materials owing to their diverse crystal structures and chemical compositions. Nevertheless, understanding the mechanism behind excitation-dependent emissions (EDEs) in 0D HMHs and achieving precise modulation remains challenging. In this work, the delicate regulations on the EDE of 0D (DMEDABr)4SnBr3I3 (DMEDA: N, N′-dimethylethylenediamine) with mixed halogens are achieved under low temperature and high pressure, respectively. The inhomogeneous halogen occupation at the atomic scale leads to the formation of Br-rich and I-rich SnX6 (X = Br, I) octahedra, which act as distinct luminescent centers upon photoexcitation. At low temperatures, the narrowed photoluminescence spectra could distinguish the individual emissions from different luminescent centers, resulting in a pronounced EDE of (DMEDABr)4SnBr3I3. In addition, the contraction and distortion of the luminescent SnX6 (X = Br, I) centers at high pressure further result in different degrees of emission shifts, giving rise to the gradual emergence and disappearance of EDE. This work elucidates the underlying mechanism of EDE in 0D HMHs and highlights the crucial role of halogens in determining the optical properties of metal halides. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have brought about a disruptive shift in the field of third-generation photovoltaics. Their potential as remarkably efficient solar cell absorbers was first demonstrated in the beginning of the 2010s. However, right from their inception, persistent challenges have impeded the smooth adoption of this technology in the industry. These challenges encompass issues such as the lack of reproducibility in fabrication, limited mid- and long-term stability, and concerns over toxicity. Despite achieving record efficiencies that have outperformed even well-established technologies, such as polycrystalline silicon, these hurdles have hindered the seamless transition of this technology into industrial applications. In this Perspective, we discuss which of these challenges are rooted in the unique dual nature of metal halide perovskites, which simultaneously function as electronic and ionic semiconductors. This duality results in the intermingling of processes occurring at vastly different timescales, still complicating both their comprehensive investigation and the development of robust and dependable devices. Our discussion here undertakes a critical analysis of the field, addressing the current status of knowledge for devices based on halide perovskites in view of electronic and ionic conduction, the underlying models, and the challenges encountered when these devices are optoelectronically characterized. We place a distinct emphasis on the positive contributions that this area of research has not only made to the advancement of photovoltaics but also to the broader progress of solid-state physics and photoelectrochemistry. [ABSTRACT FROM AUTHOR]

We investigated the impact of carrier trapping on the carrier lifetime of metal halide perovskite materials, which are key to solar cell production. We examined NH3CH3PbI3 (MAPbI3), NH3CH3PbBr3 (MAPbBr3), and CsPbBr3 using continuous-wave (CW) laser illumination during microwave photoconductivity decay (μ-PCD) measurements. Traditional pulsed light excitation falls short of mirroring solar cell operating conditions, owing to carrier trapping. Implementing CW laser illumination provides a more accurate estimation of the carrier lifetimes under operational conditions. With an increased photon flux from the CW laser, the μ-PCD decay curves changed, indicating reduced recombination via traps. The experiments revealed extended carrier lifetimes under continuous light for the MAPbI3 polycrystal. This suggests that CW lasers can mitigate trapping effects on carrier lifetime measurements. For the other samples, carrier trapping had a negligible effect on the measured carrier lifetimes. We believe that these findings will aid in the design of perovskite-based devices. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have emerged as the most promising materials due to superior optoelectronic properties and great applications spanning from photovoltaics to photonics. Absorption spectroscopy provides a broad and deep insight into the carrier dynamics of MHPs, and is a critical complement to fluorescence and scattering spectroscopy. However, absorption spectroscopy is often misunderstood or underestimated, being seen as UV-vis spectroscopy only, which can lead to various misinterpretations. In fact, absorption spectroscopy is one of the most important branches of spectroscopic techniques (others including fluorescence and scattering), which plays a critical role in understanding the electronic structure and optoelectrical dynamics of MHPs. In this tutorial, the basic principles of various types of absorption spectroscopy as well as their recent developments and applications in MHP materials and devices are summarized, covering comprehensive advances in steady state and transient absorption spectroscopy. Given the significance of absorption spectroscopy in directing the design of different optoelectronic applications of MHPs, this tutorial will comprehensively discuss absorption spectroscopy, covering wavelengths from optical to terahertz (THz) and microwave, and timescales from femtoseconds to hours, and it specifically focuses on time-dependent steady-state and transient absorption spectroscopy under light illumination bias to study MHP materials and devices, allowing researchers to select suitable characterization techniques. [ABSTRACT FROM AUTHOR]

Recently, low-dimensional organic–inorganic metal halide perovskites acting as white-light-emitting materials have been widely studied in the field of optoelectronics and solid-state lighting owing to their facile preparation and excellent optical characteristics. However, the luminescence efficiency and light stability of white-light-emitting diodes (WLEDs) are hindered by the re-absorption of mixing phosphors due to the difference in light decay. Herein, we report for the first time a new zero-dimensional (0D) cadmium halide of (BAPPz)Cd2Br8·2H2O with [CdX4]2− as an optically active center, which emits broadband yellow light with a PLQY of 13.78%. Significantly, (BAPPz)Cd2Br8·2H2O could be used as a new phosphor for a white-light-emitting diode doped with a trace of blue commercial phosphor, which achieved a high color rendering index (CRI) of 93.7 and had a correlated color temperature (CCT) close to the domestic standard light source D65 (6500 K). With the driving current of the WLED device increasing from 20 mA to 120 mA, CRI values were consistently high (>90). This work not only demonstrates a new orientation to fabricate light-emitting diodes with high CRI values but also highlights its potential application in the development of energy-efficient white-light-emitting diodes. [ABSTRACT FROM AUTHOR]

Recently, metal halides have attracted much attention due to their fascinating optical properties. However, achieving efficient white emission with ultralong afterglow remains a great challenge. Herein, we report Sb3+/Mn2+-codoped CsCdCl3 and multiple emission bands can be observed, which are derived from the self-trapped exciton emission of the Sb–Cl moiety and the d–d transition of Mn2+. Thus, tunable emission from cyan to orange light can be obtained. Moreover, efficient white emission with a luminous efficiency of 74% is observed when the energy-transfer efficiency from Sb3+ to Mn2+ is 34.5%. In particular, Sb3+/Mn2+-codoped CsCdCl3 shows bright orange afterglow emission, and the afterglow intensity is 1000 times that of CsCdCl3 and 20 times that of CsCdCl3:Mn2+. Upon combining this with thermoluminescence spectra, it is found that Mn2+/Sb3+ codoping can effectively regulate the depth and density distribution of trap defects, resulting in the ultralong afterglow duration exceeding 12 h at room temperature. Surprisingly, white light stimulation can provide additional photonic energy for Sb3+/Mn2+-codoped CsCdCl3, which enables the rapid release of trapped carriers to the emission center and rejuvenates afterglow emission after 12 h pre-delay. Finally, we demonstrated the applications of the as-synthesized compounds in single-component white light illumination, multiple optical anti-counterfeiting and information encryption. [ABSTRACT FROM AUTHOR]

The Bridgman method for single-crystal growth enables the formation of crystals at the lower end of the molten material by cooling it under a precisely controlled temperature gradient. This makes it particularly suitable for producing high-quality single-crystal materials. Over the years, the Bridgman technique has become widely adopted for growing single crystals of semiconductors, oxides, sulfides, fluorides, as well as various optoelectronic, magnetic, and piezoelectric materials. Recently, there has been growing interest in metal halide materials, with the growth of high-quality metal halide single crystals emerging as a major focus for both the scientific community and industry. However, traditional solution-based single-crystal growth methods have several limitations, such as slow growth rates, inconsistent crystal quality, challenges in solvent selection, and difficulties in controlling saturation levels. These issues present significant obstacles, particularly when large, defect-free, high-quality single crystals are needed for certain high-performance materials. As a result, the Bridgman method has emerged as an effective solution to overcome these challenges. This review provides an overview of various categories of metal halide single-crystal systems grown using the Bridgman method in recent years. The systems are classified based on their dimensionality into three-dimensional, two-dimensional, and zero-dimensional metal halide structures. Furthermore, we highlight novel metal halide single crystals developed through the Bridgman technique. Additionally, we offer a brief introduction to the structures, properties, and applications of these single crystals, underscoring the crucial role of the Bridgman method in advancing research in this field. [ABSTRACT FROM AUTHOR]

Metal halide perovskite quantum dots (MHP QDs), as a kind of fluorescent material, have attracted much attention due to their excellent photoluminescence (PL) quantum yield (QY), narrow full width at half maximum (FWHM), broad absorption, and tunable emission wavelength. However, the instability and biological incompatibility of MHP QDs greatly hinder their application in the field of biomedicine. Hydrogels are three-dimensional polymer networks that are widely used in biomedicine because of their high transparency and excellent biocompatibility. This review not only introduces the latest research progress in improving the mechanical and optical properties of hydrogels/MHP QDs but also combines it with the existing methods for enhancing the stability of MHP QDs in hydrogels, aiming to provide new ideas for researchers in material selection and methods for constructing MHP QD-embedded hydrogels. Finally, their application prospects and future challenges are introduced. [ABSTRACT FROM AUTHOR]

The ionic conduction properties of Li/Na metal halides have been extensively studied, with recent attention turning towards Al-based systems. However, limited studies have focused on alkali Al bromides. In this study, we explored the Na+ conduction properties of NaAlBr4. Conductivity measurements at 30 °C revealed a Na+ conductivity of 1.2 × 10−5 S/cm, surpassing that of isostructural NaAlCl4 threefold. Molecular dynamics (MD) simulations to elucidate the conduction mechanisms revealed that Na+ conduction was not observed in stoichiometric NaAlBr4, which has high formation energies of Na+ vacancies and interstitials (0.88 eV and 0.73 eV, respectively). Nevertheless, a conductivity of 1.2 × 10−5 S/cm was observed. The activation energy for ion conduction was experimentally determined as 0.43 eV, and the migration energies were calculated as 0.26 eV (Na+ vacancies) and 0.16 eV (Na+ interstitials) by MD simulations. These discrepancies in ion conduction were partially explained by the role of transient defects enriched via ball milling in facilitating Na+ conduction on the particle surface, offering insights into the complex ion conduction of ball-milled NaAlBr4. [ABSTRACT FROM AUTHOR]

The use of organic halide salts to passivate metal halide perovskite (MHP) surface defects has been studied extensively. Passivating the surface defects of the MHP is of critical importance for realizing highly efficient and stable perovskite solar cells (PSCs). Here, the successful application of a multifunctional organic salt, methyltriphenylphosphonium iodide (MTPPI), used as a passivation additive for grain boundary defects and as a molecular sealing layer in terms of stabilization, has been used to stabilize the mixed cation perovskite RbCsMAFA-PbIBr. To assess the passivating and stabilizing effects of MTPPI on RbCsMAFA-PbIBr PSCs, maximum power point tracking (MPPT) was applied as the most realistic and closest-to-application condition for the ageing test. Here, perovskite solar cells were aged under a light source yielding an excitation intensity corresponding to one sun with maximum power point tracking, which was interrupted periodically by current–voltage sweeps. This allowed for the extraction of all photovoltaic parameters necessary for a proper understanding of the ageing process. The MTPPI additive can donate iodine anions to halide vacancies and compensate a negative surface excess charge with cation interactions. On top of this, the large and bulky methyltriphenylphosphonium (MTPP+) cation may block both the escape of volatile perovskite components and the ingress of oxygen and water vapour. These collective roles of MTPPI have improved both the efficiency and stability of the solar cells compared to the reference without passivation additives. [ABSTRACT FROM AUTHOR]

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Functional materials, possessing specific properties and performing particular functions beyond their mechanical or structural roles, are the foundation of modern matter science including energy, environment, and quantum sciences. The atomic and electronic structures of these materials can be significantly altered by external stimuli such as pressure. High-pressure techniques have been extensively utilized to deepen our understanding of structure–property relationships of materials, while also enabling emergent or enhanced properties. In this feature article, we review the transformative impact of high pressure on the chemical and physical properties of functional materials, including perovskite materials, low-dimensional metal halides, metal chalcogenides, metal oxides, and inorganic molecular crystals. By analyzing recent advancements and methodological approaches in high-pressure research, we provide insights into the mechanisms driving structural and property changes in these materials. We also emphasize the significance of translating the knowledge gained from high pressure research to the design of new functional materials. Finally, we highlight the potential of high-pressure chemistry and nano-architectonics in advancing functional materials and discuss the future directions and challenges in this field. [ABSTRACT FROM AUTHOR]

[Display omitted] • A spatial-time-dual-resolved PL switching system based on 0D Mn-based metal halides. • Excellent reversible phase conversion properties between crystalline and molten states. • Superior PL switching with short response times and ultrahigh cyclic reversibility. • Screen printing fluorescent security labels with high spatial resolution and convenience. • Versatile multi-level information encryption-decryption and anti-counterfeiting. 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) 2 MnBr 4 (named M−1 , EMMZ=1-Ethyl-3-Methylimidazolium Bromide) and (EDMMZ) 2 MnBr 4 (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. [ABSTRACT FROM AUTHOR]

0D Hybrid Zn/Cd Halied for Color-Time-Dual-Resolved Security Applications: We devise a family of zero-dimensional (0D) hybrid metal halides based RTP materials with dual phosphorescence performance and adjustable lifetime scale, which realize color-lifetime-dual-resolved encoding ability, showcasing potential applications in multilevel anti-counterfeiting and information security. [Display omitted] • A new optical multiplexing concept of simultaneously utilizing the varied emission color and lifetime as dual temporary codes was proposed. • A new family of zero-dimensional (0D) organic metal halides was directly synthesized accompanied by tailorable lifetime at the same molecular platform. • High-security anti-Counterfeiting and 4D information encryption-decryption were demonstrated. Luminescent materials with engineered optical properties play an important role in anti-counterfeiting and information security technology. However, conventional luminescent coding is limited by fluorescence color or intensity, and high-level multi-dimensional luminescent encryption technology remains a critically challenging goal in different scenarios. To improve the encoding capacity, we present an optical multiplexing concept by synchronously manipulating the emission color and decay lifetimes of room-temperature phosphorescence materials at molecular level. Herein, we devise a family of zero-dimensional (0D) hybrid metal halides by combining organic phosphonium cations and metal halide tetrahedral anions as independent luminescent centers, which display blue phosphorescence and green persistent afterglow with the highest quantum yields of 39.9 % and 57.3 %, respectively. Significantly, the luminescence lifetime can be fine-tuned in the range of 0.0968–0.5046 μs and 33.46–125.61 ms as temporary time coding through precisely controlling the heavy atomic effect and inter-molecular interactions. As a consequence, synchronous blue phosphorescence and green afterglow are integrated into one 0D halide platform with adjustable emission lifetime acting as color- and time-resolved dual RTP materials, which realize the multiple applications in high-level anti-counterfeiting and information storage. The color-lifetime-dual-resolved encoding ability greatly broadens the scope of luminescent halide materials for optical multiplexing applications. [ABSTRACT FROM AUTHOR]

Engineering the surface of metal halide perovskite nanocrystals (MHPNCs) is crucial for optimizing their optical properties, repairing surface defects, enhancing quantum yield, and ensuring long-term stability. These enhancements make surface-engineered MHPNCs ideal for applications in light-emitting devices (LEDs), displays, lasers, and photodetectors, contributing to energy efficiency. This article delves into an introduction to MHPNCs, their structure and types, particularly the ABX3 type (where A represents monovalent organic/inorganic cations, B represents divalent metal ions mainly Pb metal, and X represents halide ions), synthesis methods, unique optical properties, surface modification techniques using various agents (particularly inorganic molecules/materials, organic molecules, polymers, and biomolecules) to tune optical properties and applications in the aforementioned light-emitting technologies, challenges and opportunities, including advantages and disadvantages of surface-modified APbX3 MHPNCs, and a summary and future outlook. This article explores surface modification strategies to improve the optical performance of MHPNCs and aims to inspire advancements in light emitting applications. Importantly, the challenges and opportunities section of this article will illuminate the path to overcoming obstacles, providing invaluable insights for researchers in this field. This in-depth review explores the surface engineering of MHPNCs for light-emitting applications, highlighting their notable advantages and addressing ongoing challenges. By delving deep into various surface modification strategies, this article aims to revolutionize MHPNC-based light-emitting applications, setting a new benchmark in the field. This paves the way for revolutionary advancements, maximizing the capabilities of surface-engineered MHPNCs and heralding a transformative era in precise light-emitting research. [ABSTRACT FROM AUTHOR]

Metal halide (MH) scintillators serve as a compelling substitute for traditional scintillators in x-ray detection and imaging due to their low-temperature fabrication process, high light yield and mechanical flexibility. Nevertheless, the spatial resolution and photoluminescence quantum yield (PLQY) of these films are hindered by the agglomeration and uneven distribution of MHs crystal particles during the fabrication process. We introduce a modified fabrication approach for MH scintillator films involving an additional step of ethyl acetate (EA) treatment, resulting in the preparation of a smooth EA-treated (Ph4P)2MnBr4/Polydimethylsiloxane film (Ph4P = Tetraphenylphosphonium). The carbonyl groups within EA interact with elements of the (Ph4P)2MnBr4 microcrystals powder, ensuring uniform dispersion and preventing agglomeration. The EA-treated composite film demonstrates a remarkable PLQY of approximately 95.8% and an impressive spatial resolution of 14 lp mm−1, with enhanced stability under harsh environments. These characteristics ensure its suitability as a high-performance x-ray imaging scintillator. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) exhibit unusual properties and complex dynamics. By combining ab initio time-dependent density functional theory, nonadiabatic molecular dynamics and machine learning, we advance quantum dynamics simulation to nanosecond timescale and demonstrate that large fluctuations of MHP defect energy levels extend light absorption to longer wavelengths and enable trapped charges to escape into bands. This allows low energy photons to contribute to photocurrent through energy up-conversion. Deep defect levels can become shallow transiently and vice versa, altering the traditional defect classification into shallow and deep. While defect levels fluctuate more in MHPs than traditional semiconductors, some levels, e.g., Pb interstitials, remain far from band edges, acting as charge recombination centers. Still, many defects deemed detrimental based on static structures, are in fact benign and can contribute to energy up-conversion. The extended light harvesting and energy up-conversion provide strategies for design of novel solar, optoelectronic, and quantum information devices. [ABSTRACT FROM AUTHOR]

N-Methyl-2-hydroxy-1-ethanaminium lead iodide exhibits a low melting temperature (Tm = 99 °C) among 2D hybrid metal halides (HMHs). This discovery expands the low melting characteristics of 2D HMHs to include a stepped 9R-like structure, suggesting significant potential for melt-processing and hybrid glass formation. [ABSTRACT FROM AUTHOR]

In recent years, lead-free organic–inorganic hybrid zero-dimensional metal halides have attracted considerable attention due to their outstanding optical properties, largely attributed to the confinement of localized metal groups. We report the discovery of a newly structured [MMim]2[CuI3] crystal with a distinct [CuI3]2− trigonal planar structure encapsulated by inert organic [MMim]+ clusters. The structure, composition, and thermal stability of the crystal were analyzed using XRD and TG–DTA. The optical properties of [MMim]2[CuI3] crystals were both experimentally measured and theoretically calculated. These crystals exhibit intense broadband orange luminescence with pronounced Stokes shifts and a microsecond-scale fluorescence lifetime decay, primarily due to self-trapped exciton emission. Temperature-dependent fluorescence spectra were also recorded to explore the luminescence mechanism. In summary, these findings highlight the remarkable potential of lead-free [MMim]2[CuI3] crystals in advancing optoelectronic applications. [ABSTRACT FROM AUTHOR]

Zero-dimensional (0D) chiral hybrid metal halides (HMHs) with narrow-band circularly polarized luminescence (CPL) show considerable promise in three-dimensional displays. In this work, 0D (S/R-3MOR)3TbCl6 and (S/R-3MOR)3EuCl6 (abbreviated as S/R-TbCl, S/R-EuCl) enantiomers with characteristic rare-earth ion emissions are synthesized. S/R-TbCl and S/R-EuCl exhibit narrow-band green and red emissions with high photoluminescence quantum yields of (85–91)% and (48–52)%, respectively. These materials present distinct CPL signals with dissymmetry factors up to ±0.006 and ±0.009 for S/R-TbCl and S/R-EuCl, respectively. These chiroptical properties confer the potential for their applications in circularly polarized light-emitting diodes for future displays. [ABSTRACT FROM AUTHOR]

Zero-dimensional (0D) organic-inorganic hybrid metal halide material (OIMH) [C3H6NH2]2CoBr4 (C3H6NH2 = azetidine cation) was successfully synthesized and carried out a series of characterizations. A comparison with [C3H6NH2]2CoCl4 was then conducted. It was found that after the anionic halogen substitution, the dielectric switching properties remained essentially consistent, and the main reason for the phase transition was the cationic order-disorder motion. However, the phase transition temperature (TC) of [C3H6NH2]2CoBr4 is 364.5 K, which is 16.8 K higher than that of [C3H6NH2]2CoCl4. Calculations revealed that the void occupancy between cations and anions decreased from 32.49% in [C3H6NH2]2CoCl4 to 29.77% in [C3H6NH2]2CoBr4, and due to the reduction in porosity, the temperature required for cationic order-disorder motion is therefore higher. Additionally, the analysis of the Hirshfeld surface and two-dimensional fingerprints revealed that the proportion of intermolecular hydrogen bond interactions in [C3H6NH2]2CoBr4 (47.1%) is higher than in [C3H6NH2]2CoCl4 (45.75%), and there is also an enhancement in the non-covalent interaction energies between cations and anions (the non-covalent interaction energies between cations and anions in [C3H6NH2]2CoCl4 are –6.9 and –8.7 kJ/mol, while in [C3H6NH2]2CoBr4 they are –7.6 and –20.9 kJ/mol, which is also the reasons for the increase in TC. Furthermore, we observed that as the volume of anions in the inorganic framework increased, the band gap value also showed a decreasing trend, from 4 eV for [C3H6NH2]2CoBr4 to 3.678 eV for [C3H6NH2]2CoCl4. [ABSTRACT FROM AUTHOR]

The title compound, {(C2H8NO)2[SnBr4]}n, is a layered hybrid perovskite crystallizing in the monoclinic space group C2/c. The asymmetric unit consists of one H3C--O--NH2 +--CH3 cation (Me2HA+), one SnII atom located on a twofold rotation axis, and two Br atoms. The SnII atom has a distorted octahedral coordination environment formed by the bromido ligands. The {SnBr6} units corner-share their equatorial Br atoms, forming infinite mono-layers that extend parallel to the ab plane. These inorganic layers are sandwiched by the organic Me2HA+ cations organized in double-layers; stacking of the layers is along the c-axis direction. Consecutive inorganic layers, separated by the organic cations, are shifted relative to each other along the b-axis direction. Specifically, the SnII atom in one inorganic layer is offset by 3.148 A ° along the b axis relative to the SnII atom in an adjacent inorganic layer. The N,O-dimethylhydroxylammonium cation forms two hydrogen bonds with the axial bromide anions of the inorganic layers as acceptors, and leads to the cohesion of the crystal structure. According to Hirshfeld surface analysis, the highest contributions to the crystal packing are from H···H (46.2%), Br···H (38.5%), and H···O (14.8%) contacts. [ABSTRACT FROM AUTHOR]

The title compound is a germanium-based hybrid metal halide that represents a less-toxic alternative to more popular lead-based analogues in optoelectronic applications. {(2-IC2H4NH3)2[GeI4]}n is composed of infinite inorganic layers that are formed by [GeI6]4 octahedra connected in a corner-sharing manner with four equatorial I atoms. The organic (2-IC2H4NH3)+ cations interleave the inorganic layers. There are two types of 2-iodoethylammonium cations, with synclinal and antiperiplanar conformations. The organic cations interact with the inorganic layers through hydrogen bonds and I...I contacts. The crystal under investigation was twinned by a 180° rotation around [100]. [ABSTRACT FROM AUTHOR]

Glass, with its unique amorphous properties, offers low thermal conductivity, high catalytic activity, insensitivity to interfacial lattice mismatch, and the absence of grain boundaries. Melt‐quenched organic–inorganic hybrid glass has recently gained significant attention as an emerging material because of its excellent processability and formability. Here, an SbCl3(C25H46ClN)x halide with a low melting point (90 °C) and significant formability is reported. Both the crystalline and glass states of SbCl3(C25H46ClN)x have double broadband emission, and the glass state exhibits negative thermal quenching, which is rare in metal halides. Interestingly, the luminescence properties of SbCl3(C25H46ClN)x glass with different x values differ. This feature is utilized to design multimodal anti‐counterfeiting and information encryption applications. Additionally, The inherent melt processing capability of SbCl3(C25H46ClN)x allows it to be shaped into various forms suitable for practical applications. SbCl3(C25H46ClN)x scintillator screens (diameter 2.2 cm) are successfully prepared by low‐temperature melting, achieving an X‐ray imaging resolution of 18 line pairs per millimeter (18 lp mm−1). This study demonstrates the potential of melt‐processed organic–inorganic hybrid glass SbCl3(C25H46ClN)x in anti‐counterfeiting, information encryption, and X‐ray detection. [ABSTRACT FROM AUTHOR]

Exploring structural phase transitions and luminescence mechanisms in zero‐dimensional (0D) metal halides poses significant challenges, that are crucial for unlocking the full potential of tunable optical properties and diversifying their functional capabilities. Herein, we have designed two inter‐transformable 0D Cu(I)‐based metal halides, namely (C19H18P)2CuI3 and (C19H18P)2Cu4I6, through distinct synthesis conditions utilizing identical reactants. Their optical properties and luminescence mechanisms were systematically elucidated by experiments combined with density functional theory calculations. The bright cyan‐fluorescent (C19H18P)2CuI3 with high photoluminescence quantum yield (PLQY) of 77 % is attributed to the self‐trapped exciton emission. Differently, the broad yellow‐orange fluorescence of (C19H18P)2Cu4I6 displays a remarkable PLQY of 83 %. Its luminescence mechanism is mainly attributed to the combined effects of metal/halide‐to‐ligand charge transfer and cluster‐centered charge transfer, which effects stem from the strong Cu−Cu bonding interactions in the (Cu4I6)2− clusters. Moreover, (C19H18P)2CuI3 and (C19H18P)2Cu4I6 exhibit reversible structural phase transitions. The elucidation of the phase transitions mechanism has paved the way for an unforgeable anti‐counterfeiting system. This system dynamically shifts between cyan and yellow‐orange fluorescence, triggered by the phase transitions, bolstering security and authenticity. This work enriches the luminescence theory of 0D metal halides, offering novel strategies for optical property modulation and fostering optical applications. [ABSTRACT FROM AUTHOR]

In recent years, perovskite light‐emitting diodes have witnessed a remarkable evolution in both efficiency and luminance levels. Nonetheless, the production of such devices typically relies on protracted synthesis procedures at elevated temperatures and vacuum/inert conditions (e.g. hot‐injection synthesis), thus rendering them technically unsuitable for extensive display and/or lighting applications manufacturing. Although alternative synthetic protocols have been proposed, e.g. ligand‐assisted reprecipitation, ultrasonic and microwave‐based methods, their suitability for the construction of high‐performing light‐emitting diodes has been reported in only a few studies. In this study, we demonstrate the fabrication of highly efficient lighting devices based on CsPbBr3 colloidal perovskite nanocrystals synthesized by a fast, energetically efficient, and up‐scalable microwave‐assisted method. These nanocrystals exhibit an impressive photoluminescence quantum yield of 66.8% after purification, with a very narrow PL spectrum centered at 514 nm with a full width at half‐maximum of 20 nm. Similarly, the PeLEDs achieve a maximum external quantum efficiency of 23.4%, a maximum current efficiency of 71.6 Cd A−1, and a maximum luminance level that exceeds 4.7 × 104 Cd m−2. Additionally, a significantly lower energy consumption for microwave‐mediated synthesis compared with hot injection is demonstrated. These findings suggest that this synthetic procedure emerges as an outstanding and promising method towards a scalable and sustainable fabrication of high‐quality perovskite light‐emitting diodes. [ABSTRACT FROM AUTHOR]

Metal halide perovskite nanocrystals have been under intense investigation for their promise in optoelectronic devices due to their remarkable physics, such as liquid/solid duality. This liquid/solid duality may give rise to their defect tolerance and other such useful properties. This duality means that the electronic states are fluctuating in time, on a distribution of timescales from femtoseconds to picoseconds. Hence, these lattice induced energy fluctuations that are connected to polaron formation are also connected to exciton formation and dynamics. We observe these correlations and dynamics in metal halide perovskite nanocrystals of CsPbI3 and CsPbBr3 using two-dimensional electronic (2DE) spectroscopy, with its unique ability to resolve dynamics in heterogeneously broadened systems. The 2DE spectra immediately reveal a previously unobserved excitonic splitting in these 15 nm NCs that may have a coarse excitonic structure. 2D lineshape dynamics reveal a glassy response on the 300 fs timescale due to polaron formation. The lighter Br system shows larger amplitude and faster timescale fluctuations that give rise to dynamic line broadening. The 2DE signals enable 1D transient absorption analysis of exciton cooling dynamics. Exciton cooling within this doublet is shown to take place on a slower timescale than within the excitonic continuum. The energy dissipation rates are the same for the I and Br systems for incoherent exciton cooling but are very different for the coherent dynamics that give rise to line broadening. Exciton cooling is shown to take place on the same timescale as polaron formation, revealing both as coupled many-body excitation. [ABSTRACT FROM AUTHOR]

[Display omitted] The multifunctional and reversible stimuli-responsive luminescence switching offers significant potential for advanced photonic applications but presents considerable challenges for zero-dimensional (0D) hybrid halides. In this study, we design two 0D Mn(II)-based hybrid halides, (DMAP) 2 MnCl 4 ·H 2 O and (DMAP) 2 MnCl 4 (DMAP = protonated 4-dimethylaminopyridine), which demonstrate reversible photoluminescence (PL) and radioluminescence (RL) switching through the removal/insertion of guest H 2 O and single-crystal to single-crystal (SC-SC) transformation. By employing a one-step electrospinning strategy, the composite nanofiber film benefits from geometric confinement and the superior hydrophobicity of the PVDF matrix, exhibiting excellent reversible PL switching properties, remarkable repeatability (1000 cycles), and rapid response to breath (0.6 s). Notably, the composite nanofiber film achieves a rare triple-mode reversible PL switching, including off-onI (green), color-tunable onI-onII (green-yellow), and onII (yellow)-off modes. This innovative composite holds great potential for novel applications in molecular-level dynamic photonic devices, including data storage, information security, optical logic gates, and flexible X-ray imaging. [ABSTRACT FROM AUTHOR]

We incorporate aggregation-induced luminescent molecules into the metal halide system to design (BTP) 2 ZnBr 4 single crystal, establish a dopant-induced STE state by doping Sb3+ ions to attain 725 nm near-infrared emission, red-shift the excitation wavelength to 430 nm via exploiting excited-state energy transfer. [Display omitted] • Near-infrared emission from Sb3+-activated single crystals was successfully synthesized. • Stability and rigidity are enhanced by using Zn as the matrix for [ZnBr 4 ]2− polyhedra. • Utilizing aggregation-induced emission ligands for excited-state energy transfer. • Theoretical calculations guide the doping of Sb3+ in [ZnBr 4 ]2− to promote exciton emission. Luminescent metal halides have garnered significant attention due to their tunable emission characteristics and exceptional optoelectronic properties. Nevertheless, achieving metal halides that exhibit near-infrared (NIR) emission upon blue-light excitation remains a significant challenge. In this study, blue-light-induced NIR emission was successfully realized in the zero-dimensional (0D) (BTP) 2 ZnBr 4 :Sb3+ single crystal [BTP+:(3-Bromopropyl) triphenylphosphonium cation] via a straightforward energy transfer from the host (BTP) 2 ZnBr 4 to the self-trapped exciton (STE) state generated by Sb3+. Upon excitation with blue light, (BTP) 2 ZnBr 4 :12.5 % Sb3+ exhibits broad NIR emission characterized by a peak at approximately 725 nm, a Stokes shift of about 295 nm, and a notably large full width at half maximum (FWHM) of 179 nm. Additionally, the analysis of experimental data in conjunction with density functional theory (DFT) calculations elucidated the blue light emission mechanism of the host as well as the doped NIR emission. The study demonstrated potential night vision applications by utilizing the (BTP) 2 ZnBr 4 :12.5 % Sb3+ phosphor combined with a 430 nm light-emitting diode (LED) chip in the dark. [ABSTRACT FROM AUTHOR]

First-principles density-functional theory calculations were performed to reveal the effect of surface polarization and structural deformation on the formation and stabilization of the polaron in two-dimensional Ruddlesden–Popper perovskites. Our results revealed that the orientational distribution of organic cations induces surface polarization. The surface dipole moment can be well featured by the c axis distances between N and the nearest I atoms. Structural deformation and surface dipole moments result in separate real-space distributions of hole and electron polarons. Our results also reveal that the structural deformation of the [PbI6] sublattices and surface polarization are closely related to the reorientation of organic cations and can be effectively modulated by it. This reorientation significantly impacts the stabilization of polarons. Our understandings provide insight into the nature of polarons in two-dimensional Ruddlesden–Popper perovskites and general guidance for the proper selection of organic cations in two-dimensional perovskites for suitable applications in photovoltaic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic halides have attracted widespread attention due to their multiple optical performances. The combination of distorted metal cation polyhedra and π‐conjugated organic ions is an effective strategy to derive hybrid nonlinear optical (NLO) and birefringent crystals. Here, a new acentric 4‐cyanopyridine mercury halide, (C6H5N2)HgCl3, have been obtained via replacing an inorganic cation with an organic cation based on parent compound CsHgCl3. (C6H5N2)HgCl3 shows the strongest second harmonic generation (SHG) effect among mercury‐pyridine hybrid metal halides, with an intensity of 3.04 times of KH2PO4 (KDP) at 1.064 µm laser radiation. The crystal structure of (C6H5N2)HgCl3 is composed of specially [HgCl3]∞ chains and [(C6H5N2)+] cations. Additionally, (C6H5N2)HgCl3 shows an outstanding experimental birefringence (Δn = 0.360@0.546 µm), which is the largest value among mercury‐based hybrid halides, and its birefringence is greater than those of all inorganic metal halide birefringent crystals. The discovery of (C6H5N2)HgCl3 indicates the potential advantage of mercury‐based hybrid halides in optical materials. [ABSTRACT FROM AUTHOR]

Metal halide perovskites and their nanostructures have efficient optical absorption and emission in the visible range with high external quantum efficiency. They have been at the forefront of next-generation photovoltaics and optoelectronics applications. But several intrinsic limitations of perovskites including low stability and incompatibility with lithography-based patterning constrains their broader applications. In recent years, the integration of perovskites with polymers especially multifunctional block copolymers (BCPs) has provided a new approach to overcome those issues. The chemical composition and chain architecture of BCPs are critical for achieving synergistic effects with perovskites in their hybrid systems. In this Highlight review article, we provide an overview and critical summary of the recent progress in the creation of perovskite–BCP hybrid structures, with a focus on the different roles of BCPs. The major categories include: (i) BCPs act as the nanopattern template for the spatial control and patterning of perovskite; (ii) BCP micelles or stars act as the template for perovskite nanostructure crystallization; (iii) BCPs act as the macromolecular ligands for perovskite NCs during its solution synthesis; (iv) BCP encapsulation of perovskite NCs into hierarchical composite particles; and (v) BCP incorporation into bulk perovskite and forming bulk composite films. The applications of perovskite–BCP hybrid structures in various fields and the major current challenges are also identified and discussed. [ABSTRACT FROM AUTHOR]

Research on organic–inorganic hybrid materials (OIHMs) has experienced explosive growth in the past decades. The diversity of organic components allows for the introduction of various spatial scales, functional groups, and polarities, while inorganic components provide higher hardness, heat resistance, and stability, their flexible combination facilitates the formation of diverse structures. Furthermore, simple and cost‐effective synthesis methods, such as room temperature solution processes and mechanochemical techniques, enable precise control over the materials' properties at different scales, thus achieving adjustable structure–performance relationships. This review will discuss the recent research progress of OIHMs within the field of optoelectronics and related optoelectronic device applications. According to the dimension of inorganic components and the nature of organic–inorganic interface, this review divides OIHMs into four structural categories. The ongoing research has revealed diverse applications for OIHMs in the fields of solar cells, light‐emitting devices, detectors, and memristors. As an outlook, the potential of perovskite and 0D metal halide materials, which are currently the most studied, for enhancing optoelectronic performance and stability is discussed. [ABSTRACT FROM AUTHOR]

Unlike single‐component 2D metal halide perovskites (MHPs) exhibiting sharp excitonic photoluminescence (PL), a broadband PL emerges in mixed Pb‐Sn 2D lattices. Two physical models –self‐trapped exciton and defect‐induced Stokes‐shift – are proposed to explain this unconventional phenomenon. However, the explanations provide limited rationalizations without consideration of the formidable compositional space, and thus, the fundamental origin of broadband PL remains elusive. Herein, the high‐throughput automated experimental workflow is established to systematically explore the broadband PL in mixed Pb‐Sn 2D MHPs, employing PEA (Phenethylammonium) as a model cation known to work as a rigid organic spacer. Spectrally, the broadband PL becomes further broadened with rapid PEA2PbI4 phase segregation with increasing Pb concentrations during early‐stage crystallization. Counterintuitively, MHPs with high Pb concentrations exhibit prolonged PL lifetimes. Hyperspectral microscopy identifies substantial PEA2PbI4 phase segregation in those films, hypothesizing that the establishment of charge transfer excitons by the phase segregation upon crystallization at high‐Pb compositions results in distinctive PL properties. These results indicate that two independent mechanisms—defect‐induced Stoke‐shifts and the establishment of charge transfer excitons by phase segregation—coexist which significantly correlates with the Pb:Sn ratio, thereby simultaneously contributing to the broadband PL emission in 2D mixed Pb‐Sn HPs. [ABSTRACT FROM AUTHOR]

Benefiting from the potential application as a single component white light source, the broadband self‐trapped excitons (STEs) emission in low‐dimensional metal halides has attracted wide attention. However, such broadband STE emission in metal thio‐ and seleno‐phosphates is scarce, and the formation mechanism is ambiguous. Herein, the broadband dual‐mode (red and near‐infrared) light emission and their linear polarization in orthorhombic Cu3PS3Se crystals are reported. The absorption and photoluminescence (PL) spectra show a large Stokes shift of 0.43/0.76 eV and a broad emission wavelength range of ≈200 nm, exhibiting the significant STEs feature. Transient absorption spectroscopy (TAS) reveals a broad positive photo‐induced absorption, further proving the formation of STE states. These STEs exhibit a highly linear polarized emission behavior with a degree of polarization up to 0.51. According to the excitation angles dependent polarized PL and Raman spectroscopy measurements, it is assigned that both the anisotropic optical absorption and electron‐phonon interaction contribute to the STEs emission polarization in Cu3PS3Se. These findings not only extend the STEs from metal halides to metal thio/seleno‐phosphates but also offer the potential prospects for novel optical polarizers, polarization‐sensitive photodetectors, optical and optoelectronic synaptic devices application of anisotropic STEs emission. [ABSTRACT FROM AUTHOR]

Halide anion migration in organic–inorganic metal halide perovskites significantly influences the power conversion efficiency (PCE) and hysteresis of perovskite solar cells (PSCs). These materials are sensitive to various external stimuli such as light, heat, and electrical bias, highlighting the need for novel post‐manufacturing treatment methods alongside a deeper understanding of their mechanisms. Here, a dark electro (DE) treatment is introduced that applies a negative‐positive‐negative bias to PSC under dark conditions, which is particularly effective for formamidinium (FA) lead iodide (FAPbI3) PSCs processed with a methylammonium chloride (MACl) additive. The DE treatment, followed by light soaking, results in an average PCE increase of 2.9 ± 1.8% (from an initial 18.2 ± 2.0% to 21.1 ± 0.8% after treatment) with a notable decrease in deviation. It is discovered that residual chloride anions from MACl play a critical role in the DE treatment. The migration of halide anions under a shaking electric bias is investigated using energy‐dispersive X‐ray spectroscopy (EDX) and time‐of‐flight secondary ion mass spectroscopy (TOF‐SIMS). This study elucidates the distribution and impact of residual chloride anions, providing insights into the mechanisms underlying the DE treatment. [ABSTRACT FROM AUTHOR]

All‐optical logic gates (AOLGs) have attracted considerable attention for their high computing speed, low power consumption, and parallel processing; however, chemical design of new luminescent materials is a challenge to explore a facile platform for undertaking AOLGs. Here, an AOLG system is developed based on the organic–inorganic hybrid halides [NH3(CH2)2NH3]2ZnCl6:Mn2+ with tricolor luminescence under dual‐wavelength excitation, and the intrinsic emission mechanisms are further addressed. When employing 275 and 365 nm UV excitations as input signals, the AOLGs conduct Boolean operations "OR, YES, AND" via identifying the green (G) and red (R) emissions and their intensity ratio (R/G) as output signals. This work further demonstrates the AOLG operation imaging and image processing via hybrid halide emitters, indicating promise in optical computing applications. [ABSTRACT FROM AUTHOR]

Metal halide perovskites, both lead‐based and lead‐free variants, have emerged as highly versatile materials with widespread applications across various fields, including photovoltaics, optoelectronics, and photocatalysis. This review provides a succinct overview of the recent advancements in the utilization of lead and lead‐free halide perovskites specifically in photocatalysis. We explore the diverse range of photocatalytic reactions enabled by metal halide perovskites, including organic transformations, carbon dioxide reduction, pollutant degradation, and hydrogen production. We highlight key developments, mechanistic insights, and challenges in the field, offering our perspectives on the future research directions and potential applications. By summarizing recent findings from the literature, this review aims to provide a timely resource for researchers interested in harnessing the full potential of metal halide perovskites for sustainable and efficient photocatalytic processes. [ABSTRACT FROM AUTHOR]

Given the extensive application of near‐infrared (NIR) emission, the quest for efficient and versatile NIR semiconductors have attracted tremendous attention. Leveraging trivalent rare earth (RE3+) ions doping, the integration of metal halide perovskites with RE3+ ions makes it easy to achieve NIR‐II emission (1000–1700 nm). However, although showing promise in bioimaging, optical communication, and night vision, enhancing NIR‐II emission intensity to promote further progress in real‐world applications remains a challenge. This review summarizes the recent advancements in RE3+ ion‐doped perovskite NIR semiconductors, and discusses what kind of properties are needed and how to achieve desired optical properties in various applications. The review starts with the synthesis methods for various material types with rich examples. Following this, the mechanisms of strategies for optimizing NIR luminescence performance are discussed in detail. Furthermore, the review highlights their multifunctional applications both as an electrically driven emitter in NIR light‐emitting diodes (LEDs) and as a down‐conversion emitter in photovoltaic devices (PVs) or phosphor‐converted LEDs (pc‐LEDs). Finally, insights on how to fill the gap between current research and future goals are provided. This review aims to provide a deeper understanding of RE3+ ion‐doped NIR light‐emitting perovskite materials, and to promote the exploration of efficient NIR emitters. [ABSTRACT FROM AUTHOR]