Manganese(II) in Tetrahedral Halide Environment: Factors Governing Bright Green Luminescence

Chirality and Solvent Coassist the Structural Evolution of Hybrid Manganese Chlorides with Second-Harmonic-Generation Response

Chiral hybrid metal halides have shown great potential in optoelectronics, including for spin splitting, circularly polarized luminescence, and nonlinear-optical properties. However, despite their inherent inversion symmetry breaking, studies on second harmonic generation (SHG) of chiral hybrid manganese(II) halides remain relatively rare. Here, we report a series of structurally diverse hybrid manganese(II) chlorides: (Rac-MBA)2[MnCl4(H2O)2] (1), (S-MBA)2[MnCl4(H2O)2] (2), (S-MBA)2[Mn2Cl6(H2O)4] (3), and (S-MBA)[MnCl3(MeOH)] (4), where MBA = α-methylbenzylammonium, providing tunability of the coordination environment and structural dimensionality via fine control of the MBA cation chiral state and crystal preparation process, thereby enabling modulation of the SHG effects. Specifically, as the amount of methanol increases during the crystal preparation process, the structures of the chiral compounds vary from a 0D structure consisting of isolated octahedra to a 0D structure composed of octahedra dimers and to 1D chains of edge-sharing Mn-centered octahedra. In contrast, the structure of the racemic compound remains unchanged, independent of the crystal preparation pathway. The structural details, including the coordination environment, H-bonding, dimensionality, and lattice distortion, are described. The SHG response of the racemic compound derives only from the inorganic lattice, while the responses of the chiral compounds are attributed to the synergetic effect of the chiral cations and inorganic moieties.

Discerning the Structure-Photophysical Property Correlation in Zero-Dimensional Antimony(III)-Doped Indium(III) Halide Hybrids

Zero-dimensional (0D) metal halide hybrids incorporating optically emissive Sb3+ dopants have received huge research attention as a result of dopant-based visible emission for lighting and scintillation applications. Indeed, there have been a plethora of reports on Sb3+ doping of indium halide (In-X)-based 0D hybrids that show strong dopant emission with varied emission wavelengths (λem) and photoluminescence quantum yields (PLQYs). However, discerning the structure-luminescence relation in these 0D-doped hybrids remains challenging because it necessitates exquisite synthetic control on the local metal (dopant) halide geometry/site asymmetry. Demonstrated here is synthetic control that allows tuning of the local metal halide geometry of the Sb3+ dopants in 0D In-X hybrids utilizing five different organic cations. Experimental analysis of the series of Sb3+-doped In-X hybrids reveals a strong correlation between the extent of local metal halide geometry distortion and their photophysical properties (λem and PLQY). Density functional theory calculations of the doped compounds, characterizing ground- and excited-state structural distortions and energetics, reveal the origin of the extent of luminescence behavior. The experimental-computational results reported herein unravel the operative structure-luminescence relation in 0D Sb3+-doped In-X hybrids, provide insight into the emission mechanism, and open up avenues toward rational synthesis of strongly emissive materials with desired emission color for targeted applications.

Unlocking the Potential of Organic-Inorganic Hybrid Manganese Halides for Advanced Optoelectronic Applications

Organic-inorganic hybrid manganese(II) halides (OIMnHs) have garnered tremendous interest across a wide array of research fields owing to their outstanding optical properties, abundant structural diversity, low-cost solution processibility, and low toxicity, which make them extremely suitable for use as a new class of luminescent materials for various optoelectronic applications. Over the past years, a plethora of OIMnHs with different structural dimensionalities and multifunctionalities such as efficient photoluminescence (PL), radioluminescence, circularly polarized luminescence, and mechanoluminescence have been newly created by judicious screening of the organic cations and inorganic Mn(II) polyhedra. Specifically, through precise molecular and structural engineering, a series of OIMnHs with near-unity PL quantum yields, high anti-thermal quenching properties, and excellent stability in harsh conditions have been devised and explored for applications in light-emitting diodes (LEDs), X-ray scintillators, multimodal anti-counterfeiting, and fluorescent sensing. In this review, the latest advancements in the development of OIMnHs as efficient light-emitting materials are summarized, which covers from their fundamental physicochemical properties to advanced optoelectronic applications, with an emphasis on the structural and functionality design especially for LEDs and X-ray detection and imaging. Current challenges and future efforts to unlock the potentials of these promising materials are also envisioned.

Direct Evidence of the Effect of Water Molecules Position in the Spectroscopy, Dynamics, and Lighting Performance of an Eco-Friendly Mn-Based Organic-Inorganic Metal Halide Material for High-Performance LEDs and Solvent Vapor Sensing

Luminescent Mn(II)-based organic-inorganic hybrid halides have drawn attention as potential materials for sensing and photonics applications. Here, the synthesis and characterization of methylammonium (MA) manganese bromide ((MA)nBrxMn(H2O)2, (n = 1, 4 and x = 3, 6)) with different stoichiometries of the organic cation and inorganic counterpart, are reported. While the Mn2+ centers have an octahedral conformation, the two coordinating water molecules are found either in cis (1) or in trans (2) positions. The photophysical behavior of 1 reflects the luminescence of Mn2+ in an octahedral environment. Although Mn2+ in 2 also has octahedral coordination, at room temperature dual emission bands at ≈530 and ≈660 nm are observed, explained in terms of emission from Mn2+ in tetragonally compressed octahedra and self-trapped excitons (STEs), respectively. Above the room temperature, 2 shows quasi-tetrahedral behavior with intense green emission, while at temperatures below 140 K, another STE band emerges at 570 nm. Time-resolved experiments (77-360 K) provide a clear picture of the excited dynamics. 2 shows rising components due to STEs formation equilibrated at room temperature with their precursors. Finally, the potential of these materials for the fabrication of color-tunable down-converted light-emitting diode (LED) and for detecting polar solvent vapors is shown.

Manipulating Chiroptical Activities in 0D Chiral Hybrid Manganese Bromides by Solvent Molecular Engineering

0D hybrid metal halides (0D HMHs) with fully isolated inorganic units provide an ideal platform for studying the correlations between chiroptical activities and crystal structures at atomic levels. Here, through the incorporation of different solvent molecules, a series of 0D chiral manganese bromides (RR/SS-C20H28N2)3MnBr8·2X (X = C2H5OH, CH3OH, or H2O) are synthesized to elucidate their chiroptical properties. They show negligible circular dichroism signals of Mn absorptions due to C2v-symmetric [MnBr4]2- tetrahedra. However, they display distinct circularly polarized luminescence (CPL) signals with continuously increased luminescence asymmetry factors (glum) from 10-4 (X = C2H5OH) to 10-3 (X = H2O). The increased glum value is structurally revealed to originate from the enhancement of [MnBr4]2- tetrahedral bond-angle distortions, due to the presence of different solvent molecules. Furthermore, (RR/SS-C20H28N2)MnBr4·H2O enantiomers with larger bond-angle distortions of [MnBr4]2- tetrahedra are synthesized based on hydrobromic acid-induced structural transformation of (RR/SS-C20H28N2)3MnBr8·2H2O enantiomers. Therefore, such (RR/SS-C20H28N2)MnBr4·H2O enantiomers exhibit enhanced CPL signals with |glum| up to 1.23 × 10-2. This work provides unique insight into enhancing chiroptical activities in 0D HMH systems.

Metal Halide Nanocrystals@Silica Aerogel Composite with Enhanced Dispersion Stability and Light Output for Efficient X-Ray Imaging in Harsh Environment

Metal halide nanocrystals (MHNCs) embedded in a polymer matrix as flexible X-ray detector screens is an effective strategy with the advantages of low cost, facile preparation, and large area flexibility. However, MHNCs easily aggregate during preparation, recombination, under mechanical force, storage, or high operating temperature. Meanwhile, it shows an unmatched refractive index with polymer, resulting in low light yield. The related stability and properties of the device remain a huge unrevealed challenge. Herein, a composite screen (CZBM@AG-PS) by integrating MHNCs (Cs2ZnBr4: Mn2+ as an example) into silica aerogel (AG) and embedded in polystyrene (PS) is successfully developed. Further characterization points to the high porosity AG template that can effectively improve the dispersion of MHNCs in polymer detector screens, essentially decreasing nonradiative transition, Rayleigh scattering, and performance aging induced by aggregation in harsh environments. Furthermore, the higher light output and lower optical crosstalk are also achieved by a novel light propagation path based on the MHNCs/AG and AG/PS interfaces. Finally, the optimized CZBM@AG-PS screen shows much enhanced light yield, spatial resolution, and temperature stability. Significantly, the strategy is proven universal by the performance tests of other MHNCs embedded composite films for ultra-stable and efficient X-ray imaging.

Centimeter-Sized Single Crystals of Tetrahedral Manganese (II) Halide Hybrids for Wide-Color Gamut Backlighting Displays

Phosphors with narrow-band green emissions and high photoluminescent quantum efficiency (PLQY) are significantly required for backlighting displays with wider color gamut. In this work, two centimeter-sized manganese (II) halide single crystals TMG2MnCl4 and TMG2MnBr4 (TMG = 1,1,3,3-tetramethylguanidine) are synthesized, exhibiting bright narrow-band green emissions with high PLQYs up to 62% and 90%, respectively. The narrow-band green light emission is located at 520 nm with a full-width at half-maximum (FWHM) of only 57 nm. The photoluminescence mechanisms of two single crystals are elaborated. Two white-light-emitting diodes for backlighting displays (BD-WLEDs) based on them are fabricated, exhibiting the widest color gamut of 122% National Television Standards Committee (NTSC), and a luminous efficacy reached ≈93 lm W-1 with excellent luminescence stability at high temperatures. These properties indicate the potential applications of tetrahedral manganese (II) hybrids in wide-color gamut backlighting displays.

Excitation-Selective and Double-Emissive Lead-Free Binary Hybrid Metal Halides for White Light-Emitting Diode and X-Ray Scintillation

Zero-dimensional (0D) organic metal halides comprising heterogeneous metal cations in single phase can achieve multiple luminous emissions enabling them toward multifunctional light-emitting applications. Herein, A novel single crystal of (C8H20N)4SbMnCl9 containing two luminescent centers of [SbCl5]2- pentahedrons and [MnCl4]2- tetrahedrons is reported. The large distance between Sb-Sb, Mn-Mn, and Sb-Mn as well as theory calculation indicate negligible interaction between individual centers, thus endowing (C8H20N)4SbMnCl9 with excitation-dependable and efficient luminescence. Under near-UV excitation, only orange emission originates from self-trapped excitons recombination in [SbCl5]2- pentahedron occurs with photoluminescence quantum yield (PLQY) of 91.5%. Under blue-light excitation, only green emission originating from 4T1-6A1 transition of Mn2+ in [MnCl4]2- tetrahedrons occurs with PLQY of 66.8%. Interestingly, upon X-ray illumination, both emissions can be fully achieved due to the high-energy photon absorption. Consequently, (C8H20N)4SbMnCl9 is employed as phosphors to fabricate white light-emitting diodes optically pumped by n-UV chip and blue-chip thanks to its excitation-dependable property. Moreover, it also shows promising performance as X-ray scintillator with low detection limit of 60.79 nGyair S-1, steady-state light yield ≈54% of commerical scintillaotr LuAG:Ce, high resolution of 13.5 lp mm-1 for X-ray imaging. This work presents a new structural design to fabricate 0D hybrids with multicolor emissions.

RGB tri-luminescence in organic-inorganic zirconium halide perovskites

Materials with two or more fluorescence features under different excitation sources have great potential in optical applications, but luminous materials with three emission characteristics have been largely undeveloped. Here, we report a novel zero-dimensional (0D) organic-inorganic hybrid ((C2H5)4N)2ZrCl6 perovskite with multiple emissions. The zirconium-based perovskite exhibits a red emission around 620 nm, a green emission at 527 nm, and a blue emission around 500 nm. The red and green emissions come from self-trapped excitons (STEs) and the d-d transitions of Zr(iv), respectively, which are caused by distortion of the [ZrCl6]2- octahedra. The blue emission is caused by thermally activated delayed fluorescence (TADF), which is similar to that of Cs2ZrCl6. The absolute photoluminescence quantum yield (PLQY) of the red and blue double emission is up to 83% and the PLQY of the green emission is 27%. With different combinations of ((C2H5)4N)2ZrCl6 samples, we achieve a variety of applications, including a two-color luminescent anti-counterfeiting device, a white light-emitting diode (WLED) with a color rendering index (CRI) of 95 and information encryption with different excitations. We also synthesize other hybrid zirconium perovskites with tri-luminescence through a similar method. Our work provides a potential set of excitation-dependent luminescent materials and is expected to expand the basic research and practical applications of multi-luminescence materials.

Optical and scintillation properties of hybrid manganese(II) bromides with formamidinium and acetamidinium cations

In recent years, hybrid manganese(II) halides (HMHs) have attracted wide attention due to their impressive optical properties, low toxicity, and facile synthetic processibility. Being effective reabsorption-free phosphors, these compounds demonstrate the potential to be used as low-cost solution-processable scintillators. However, most of the HMHs studied to date contain bulk organic cations and, as a result, are characterized by low density and low X-ray stopping power. For this reason, we studied manganese(II) bromides with compact organic cations such as formamidinium (FA+) and acetamidinium (AcA+). In particular, we synthesized four new phases, two of which are characterized by octahedral coordination of manganese ions ((FA)MnBr3 and (AcA)MnBr3) and red emission, whereas the other two have tetrahedrally coordinated Mn2+ ions ((FA)3MnBr5 and (AcA)2MnBr4) and green emission. Photoluminescence (PL) and radioluminescence measurements demonstrated high PL quantum yields and reasonable scintillation light yields of acetamidinium-based compounds. In addition, unlike most known HMH-based scintillators, the discovered materials have a relatively high density due to the small fraction of the volume occupied by organic cations, so their X-ray attenuation coefficients are comparable to the well-known oxide scintillators.

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 Hybrid Antimony Chloride with Near-Unity Broad-Band Orange-Red Emission toward Solid-State Lighting

Zero-dimensional (0D) hybrid metal halides are attractive owing to their distinctive structure as well as photoluminescence (PL) characteristics. To discover 0D hybrid metal halides with high photoluminescence quantum yield and good stability is of great significance for white light-emitting diodes (LEDs). Herein, a novel hybrid antimony chloride (CTP)2SbCl5 is synthesized, which shows a bright broad-band orange-red emission peaking at 620 nm under the low energy excitation (365 nm), achieving an excellent photoluminescence quantum yield of 96.8%. In addition, (CTP)2SbCl5 shows an additional emission peaking at 470 nm when excited at high energy (323 nm). PL spectra and density functional theory results demonstrate that the observed dual-band emission originates from the singlet and triplet self-trapped excitons confined in isolated [SbCl5]2- square pyramids. Moreover, (CTP)2SbCl5 presents relatively superior air stability, and the PL intensity still maintains 78% of the initial PL intensity when exposed to the air for above 2 weeks. Benefiting from high-efficiency PL emission and good stability of (CTP)2SbCl5, a stable warm white LED device with a 92.3% color rendering index was prepared by coating blue phosphor BaMgAl10O17:Eu2+, green (Sr,Ba)2SiO4:Eu2+, and orange-red (CTP)2SbCl5 on a 365 nm LED chip. This work provides an efficient luminescent material and also demonstrates the potential application of 0D hybrid antimony chloride in solid-state lighting.

Solid-State Synthesis and Optical Studies of Water-Stable Pb2+-Doped Mn2+ Complexes

The limited Mn2+ doping that occurs in lead halide perovskites has been widely described, while the Pb2+ doping that occurs in Mn2+ halide perovskites has not been studied well. Generally, a large amount of doping of Mn2+ in lead halide perovskite degrades the perovskite structure; eventually, high orange luminescence of Mn2+ dopant has not been achieved. In our present study, we followed a reverse strategy, i.e., Pb2+ doping in Mn2+ halide perovskites, to increase the amount of Mn2+ in halide perovskites through the high-energy ball milling method. This strategy yields bright-fluorescence orange light-emitting Mn2+-doped perovskite with a Mn/Pb ratio of 95%, which is the highest among Mn2+-doped perovskites. Zero-dimensional (0D) Mn2+ perovskites and two-dimensional (2D) Pb2+-doped Mn2+-based perovskites were successfully synthesized and characterized. During the mechanochemical engineering, Pb2+ ions partially occupy the site of Mn2+ ions and act as a luminescence activator. Mn2+-based 2D perovskites with the proper amounts of Pb2+ ions as dopant ions and phenylethylammonium (PEA+) as dielectric organic cations show enhanced stability in water. The dual-emissive properties of these 2D-Pb2+-doped Mn2+-based perovskites were also investigated by using single-particle imaging fluorescence. We believe that these findings will pave the way for designing eco-friendly dimension and bandgap tunable layered perovskites.

Photoluminescence of Mn2+ in the Borosulfate Zn[B2 (SO4 )4 ] : Mn2+ -A Tool to Detect Weak Coordination Behavior of Ligands

The impact of the surrounding ligand field is successfully exploited in the case of Eu2+ to tune the emission characteristics of inorganic photoactive materials with potential application in, e.g., phosphor-converted white light-emitting diodes (pc-wLEDs). However, the photoluminescence of Mn2+ related to intraconfigurational 3d5 -3d5 transitions is also strongly dependent on local ligand field effects and has been underestimated in this regard so far. In this work, we want to revive the idea how to electronically tune the emission color of a transition metal ion in inorganic hosts by unusual electronic effects in the metal-ligand bond. The concept is explicitly demonstrated for the weakly coordinating layer-like borosulfate ligand in the Mn2+ -containing solid solutions Zn1-x Mnx [B2 (SO4 )4 ] (x = 0, 0.03, 0.04, 0.05, 0.10). Zn[B2 (SO4 )4 ]:Mn2+ shows orange narrow-band luminescence at 590 nm, which is an unusually short wavelength for octahedrally coordinated Mn2+ and indicates an uncommonly weak ligand field. On the other hand, the analysis of the interelectronic Racah repulsion parameters reveals ionic Mn-O bonds with values close to the Racah parameters of the free Mn2+ ion. Overall, this strategy demonstrates that electronic control of the metal-ligand bond can be a tool to make Mn2+ a potent alternative emitter to Eu2+ for inorganic phosphors.

Solution-Obtained (NH4)3In0.95Sb0.05Cl6 with High External Photoluminescence Quantum Yield and Excellent Antiquenching Properties

The efficient broad-band emission from low-dimensional metal halides has garnered significant interest. However, most of these materials exhibit poor stability at the operating temperature of light-emitting diodes. In this study, using the solution method (temperature lower than 90 °C), a new compound (NH4)3In0.95Sb0.05Cl6 was obtained with the structure in the Pnma space group featuring unit-cell parameters of a = 12.3871(4) Å, b = 24.9895(9) Å, and c = 7.7844(3) Å. (NH4)3In0.95Sb0.05Cl6 can be prepared by doping (NH4)2InCl5·H2O when the Sb3+ feeding ratio is in the range of 30-80%. Thermal analysis reveals that (NH4)3In0.95Sb0.05Cl6 is stable up to 320 °C. (NH4)3In0.95Sb0.05Cl6 exhibits broad-band yellow-white emission with extremely high internal and external photoluminescence quantum yields of 93 and 77%, respectively. Interestingly, (NH4)3In0.95Sb0.05Cl6 displays remarkable resistance to thermal quenching, retaining 83% of its initial photoluminescence intensity at 80 °C. A white light-emitting diode is fabricated by combining (NH4)3In0.95Sb0.05Cl6 with a commercial phosphor, and a high color rendering of 92.8 was obtained. This work presents an environmentally friendly, efficient, stable UV-excited broad-band emission material for potential solid-state lighting applications.

Mn2+ and Sb3+ Codoped Cs2ZnCl4 Metal Halide with Excitation-Wavelength-Dependent Emission for Fluorescence Anticounterfeiting

In recent years, there has been a growing demand for luminescence anticounterfeiting materials that possess the properties of environmentally friendly, single-component, and multimode fluorescence. Among the materials explored, the low dimensional metal halides have gained wide attention because of unique characteristics including low toxicity, simple synthesis, good stability, and so on. Here, we synthesized Mn2+ and Sb3+ codoped Cs2ZnCl4 single crystals by a facile hydrothermal method. Under 365 nm excitation, the codoped compound exhibits dual-band emissions at 530 and 730 nm. However, under 316 nm excitation, the compound only shows one emission band from 500 to 850 nm peaking at 730 nm, while under 460 nm excitation, the emission from 500 to 650 nm with an emission peak at 530 nm can be observed. Based on the study of the photoluminescence mechanism, the green and red emissions originate from the Mn2+ located in the tetrahedron and self-trapped exciton emission of [SbCl4]- clusters, respectively. Due to the zero-dimensional structure of the Cs2ZnCl4 host, there is minimal energy transfer between these dopants. Consequently, the luminous ratios of the two emissions can be independently regulated. Except by tuning the dopant concentrations, the Cs2ZnCl4:Mn2+, Sb3+ demonstrates excitation-wavelength-dependent properties, which could emit more than two colors with the change of excitation wavelength. As a result, multimode anticounterfeiting based on Cs2ZnCl4:Mn2+, Sb3+ crystals has been designed, which aligns with the requirements of environmentally friendly, single-component, and multimode fluorescence properties.

High-Efficiency Narrow-Band Green-Emitting Manganese(II) Halide for Multifunctional Applications

Zero-dimensional (0D) Mn2+-based metal halides used as luminescent materials and scintillators have become a research hotspot in the field of photoelectric materials and devices due to their unique composition, structure, and fluorescence properties. It is of great value to explore new Mn2+-based metal halides to achieve multifunctional applications. Herein, the novel 0D Mn2+-based metal halide single crystal (BPTP)2MnBr4 is synthesized by a simple solvent-antisolvent recrystallization method. Under excitation at 468 nm, the (BPTP)2MnBr4 single crystal shows a pronounced narrow-band green luminescence centered at 515 nm derived from the d-d transition of the Mn2+ ion. This emission has a relatively narrow full width at half maximum of 43 nm and a high photoluminescence quantum yield (PLQY) of 82%. In addition, (BPTP)2MnBr4 exhibits good thermal stability at 393 K with a retention of 79% of the initial photoluminescence intensity at 298 K. Benefiting from its strong blue light excitation, high PLQY, and good thermal stability, we manufacture an ideal white light-emitting diode (LED) device using a 460 nm blue LED chip, green-emitting (BPTP)2MnBr4, and commercial K2SiF6:Mn4+ red phosphor. Under 20 mA drive current, the LED shows a high luminous efficiency of 112 lm/W and a wide color gamut of 110.8%, according to the National Television System Committee standard. In addition, (BPTP)2MnBr4 crystals show a strong X-ray absorption. Based on the commercial Lu3Al5O12:Ce3+ scintillator, the calculated light yield of (BPTP)2MnBr4 reaches up to about 136,000 photons/MeV and the detection limit reaches 0.282 μGyair s-1. Additionally, a melt quenching approach is used to construct a (BPTP)2MnBr4 clear glass scintillation screen, realizing a spatial resolution of 10.1 lp/mm. The proper performances of (BPTP)2MnBr4 as phosphor-converted LED materials and the X-ray scintillator with the addition of eco-friendly, low-cost solution processability make 0D Mn2+-based metal halides potential luminescent materials for multifunctional applications.

Satellite Red Emission from a Single Green-Emissive MnBr42- Tetrahedron in Soft Hybrid Single Crystals

Photoinduced self-trapped exciton emission is common in soft matter metal halide semiconductors, whereas analogous phenomena in metal halide insulators with localized emitting centers and delayed satellite emission have rarely been identified. In this study, a new zero-dimensional Mn(II) hybrid of [3DPTPP]MnBr4 (3DPTPP = (3-(dimethylamino)propyl)(triphenyl)phosphonium) with only one crystallographic Mn2+ site but dual emission is reported. The delayed red emission (∼630 nm) is successfully assigned to a satellite of the green-emissive (∼530 nm) MnBr42- tetrahedron shifted by N-H vibration (∼2500 cm-1), directly evidenced by the Raman spectra and further supported by density functional theory calculation. The photoluminescence decay curves demonstrate their same origin, but the red emission exhibits a delayed process. The temperature- and pressure-dependent PL spectra, temperature-dependent distortion of the MnBr42- tetrahedron, and light polarization spectra confirmed the consistency and distinctness of the dual emission. This study will inspire further research on self-trapped optoelectronic processes in soft metal halides.

Regulating the Optical Properties of Cs3MnBr5 Nanocrystals in Glasses for Narrow-Band Green Emission

Environmentally friendly phosphors with narrow-band green luminescence are in great demand for solid-state lighting and backlight display applications. Herein, all inorganic lead-free Cs3MnBr5 nanocrystals (NCs) are prepared in glass with dual-band luminescence and a high photoluminescence (PL) quantum yield of 60.2%. However, due to the short separation and strong coupling interaction between neighboring [ M n B r 4 ] 2 - units, Cs3MnBr5 NCs undergo energy transfer from a single [ M n B r 4 ] 2 - unit to coupled [ M n B r 4 ] 2 - clusters and give green-red dual-band PL. Incorporation of Zn into Cs3MnBr5 NCs therefore enlarges the average separation and reduces the interaction between neighboring [ M n B r 4 ] 2 - units to inhibit energy transfer from the green-emitting [ M n B r 4 ] 2 - unit to coupled [ M n B r 4 ] 2 - clusters, thus changing the dual-band PL into single-band green PL at 524 nm with a full width at half maximum of 47 nm and a maximal PL quantum yield of 50%. Low-temperature PL also demonstrates that partial replacement of Mn2+ ions by Zn2+ ions can further confine the exciton in the [ M n B r 4 ] 2 - unit and suppress the energy transfer. These Cs3MnBr5 NCs- and Zn/Cs3MnBr5 NCs-embedded glasses also possess good thermal, photo-, and chemical stabilities. These features demonstrate that these Cs3MnBr5 NCs- and Zn/Cs3MnBr5 NCs-embedded glasses have potential applications for efficient, environmental-friendly, and stable green phosphors in the fields of solid-state lighting and backlight display.

All-Inorganic Lead-Free Doped-Metal Halides for Bright Solid-State Emission from Primary Colors to White Light

Metal halides have been explored with the aid of strong photoluminescence for optical and optoelectronic applications. However, the preparation of lead (Pb)-free solid-state emitters with high photoluminescence quantum yields (PLQYs) and tunable emission remains exceptionally challenging. Herein, we report metal ion (Cu(I), Mn(II), and Sn(II))-doped Cs₃ZnI₅ single crystals that are primary color (violet, green, and orange/red) emitters with extremely high PLQYs. Whereas the Mn-doping leads to bright green emissions with 100% PLQY, the Cu- and Sn-doping give rise to blue and red emissions with PLQYs of 57 and 64%, respectively. Interestingly, higher Mn doping results in white light emissive crystals as a side product, which are found to be Mn-doped CsI single crystals. The bright white light emissive crystals can be synthesized in a pure form in large quantities and exhibit a high color rendering index (CRI) of 78 and CIE coordinates of (0.30, 0.38), which are close to daylight conditions. To the best of our knowledge, this is the first demonstration of white light emission from a complete inorganic system. Importantly, the single crystals of all colors exhibit high long-term stability as their PLQY remains unchanged even after 2 months of preparation, and are thermally stable up to 600 °C.

Green and Red Photoluminescent Manganese Bromides with Aminomethylpyridine Isomers

Two positional isomers, 4-amino-3-methylpyridine and 3-amino-5-methylpyridine, produce 4-amino-3-methylpyridinium and 5-methylpyridin-3-aminium, respectively, under acidic conditions. The two protonated isomers create different hydrogen bonding networks, resulting in different coordination environments of the [MnX₄]^2- unit embedded in molecular compounds such as 4-amino-3-methylpyridinium manganese bromide, [(C₆H₉N₂)₂MnBr₄] and 5-methylpyridin-3-aminium manganese bromide, [(C₆H₉N₂)₄MnBr₄(H₂O)·(MnBr₄)]. Both compounds can be prepared using the slow evaporation method or mechanochemical synthetic procedures. Single-crystal structure analysis of [(C₆H₉N₂)₂MnBr₄] and [(C₆H₉N₂)₄MnBr₄(H₂O)·(MnBr₄)] revealed different manganese halide units, including tetrahedral and tetrahedral with distorted trigonal bipyramidal structures, which emit photoluminescence in the green (527 nm) and red (607 nm) regions, respectively. Electronic structure calculations were conducted to support the validity and interpretation of the UV-vis and photoluminescence (PL) spectral data. Thin films deposited using the [(C₆H₉N₂)₂MnBr₄] precursor also exhibit PL properties. The diverse pseudo-three-dimensional networks can be constructed by using positional isomers with different hydrogen bonding pathways and π-π stacking of organic units, in which the design strategy successfully enables the tuning of various optical properties.

A room temperature ferroelectric material with photoluminescence: (1,3-dicyclohexylimidazole)2MnCl4

Molecular ferroelectric materials have been widely used in capacitors and sensors due to their low cost, light weight, flexibility and good biocompatibility. Organic-inorganic hybrid complexes, on the other hand, have received a great deal of attention in the luminescence field due to their low cost and simple preparation. The combination of ferroelectricity and photoluminescence in organic-inorganic hybrid materials not only leads to tunable optical properties, but also enriches potential applications of multifunctional ferroelectrics in optoelectronic devices. Here, we report a new luminescent ferroelectric material (1,3-dicyclohexylimidazole)₂MnCl₄ (DHIMC). Thermogravimetric analysis (TGA) was used to measure the mass change of the material at a measurement rate of 20 K min^-1 from room temperature to 900 K, and we found that this material has good thermostability, which is up to 383 K. Meanwhile, UV-vis measurements showed that it is also a fluorescent material emitting a strong green fluorescence at the wavelength of 525 nm. The ferroelectricity of the crystal was determined by two different methods: the Sawyer-Tower method and the double-wave method (DWM). Particularly, the single crystal experiences a phase transition from the ferroelectric phase to the paraelectric phase during the heating/cooling process at 318 K/313 K and the space group changes from P1̄ (centrosymmetric) to P1 (non-centrosymmetric). This work will enrich multifunctional luminescent ferroelectric materials and their application in display and sensing.

Solid-state synthesis of cesium manganese halide nanocrystals in glass with bright and broad red emission for white LEDs

Recently, lead halide perovskite nanocrystals (NCs) have attracted extensive attention due to their unique optical properties. However, the toxicity of lead and the instability to moisture obstruct their further commercial development. Herein, a series of lead-free CsMnX₃ (X = Cl, Br, and I) NCs embedded in glasses were synthesized by a high temperature solid-state chemistry method. These NCs embedded in glass can remain stable after soaking in water for 90 days. It is found that increasing the amount of cesium carbonate in the synthesis process can not only prevent the oxidation of Mn²⁺ to Mn³⁺ and promote the transparency of glass in the 450-700 nm region, but also significantly increase its photoluminescence quantum yield (PLQY) from 2.9% to 65.1%, which is the highest reported value of the red CsMnX₃ NCs so far. Using CsMnBr₃ NCs with a red emission peak at 649 nm and full-width-at-half-maximum (FWHM) of 130 nm as the red light source, a white light-emitting diode (LED) device with International Commission on illumination (CIE) coordinates of (0.33, 0.36) and a color rendering index (CRI) of 94 was obtained. These findings, together with future research, are likely to yield stable and bright lead-free NCs for the next generation of solid-state lighting.

Improving X-ray Scintillating Merits of Zero-Dimensional Organic-Manganese(II) Halide Hybrids via Enhancing the Ligand Polarizability for High-Resolution Imaging

Luminescent metal halides have been exploited as a new class of X-ray scintillators for security checks, nondestructive inspection, and medical imaging. However, the charge traps and hydrolysis vulnerability are always detrimental to the three-dimensional ionic structural scintillators. Here, the two zero-dimensional organic-manganese(II) halide coordination complexes 1-Cl and 2-Br were synthesized for improvements in X-ray scintillation. The introduction of a polarized phosphine oxide can help to increase the stabilities, especially the self-absorption-free merits of these Mn-based hybrids. The X-ray dosage rate detection limits reached up to 3.90 and 0.81 μGyair/s for 1-Cl and 2-Br, respectively, superior to the medical diagnostic standard of 5.50 μGyair/s. The fabricated scintillation films were applied to radioactive imaging with high spatial resolutions of 8.0 and 10.0 lp/mm, respectively, holding promise for use in diagnostic X-ray medical imaging.

Enhanced stability and complex phase behaviour of organic-inorganic green-emitting ionic manganese halides

Light-emitting materials based on earth-abundant metals, such as manganese hold great promise as emitters for organic lighting devices. In order to apply such emitter materials and, in particular, to overcome the problem of self-quenching due to cross-relaxation, we investigated a series of tetrabromidomanganate ([MnBr₄]^2-) salts with bulky tetraalkylphosphonium counter cations [P_nnn]⁺, namely [P_nnnn]₂[MnBr₄] (n = 4 (1), 6 (2) and 8 (3)), which can be obtained by a straightforward reaction of the respective phosphonium bromide and MnBr₂. Variation of the cation size allows control of the properties of the resulting ionic materials. 1 and 3 qualify as ionic liquids (ILs), where 1 features a melting point of 68 °C, and 3 is liquid at room temperature and even at very low temperatures. Furthermore, 1 and 2 show the formation of higher-ordered thermotropic mesophases. For 1 a transition to a thermodynamically metastable smectic liquid crystalline phase can be observed at room temperature upon reheating from the metastable glassy state; 2 appears to form a plastic crystalline phase at ∼63 °C, which persists up to the melting point of 235 °C. The photoemission is greatly affected by phase behaviour and ion dynamics. A photoluminescence quantum yield of 61% could be achieved, by balancing the increase in Mn²⁺-Mn²⁺ separation and reducing self-quenching through increasingly large organic cations which leads to adverse increased vibrational quenching. Compared to analogous ammonium compounds, which have been promoted as ̈inorganic hybrid perovskites̈, the phosphonium salts show superior performance, with respect to photoluminescent quantum yield and thermal and air/humidity stability. As the presented compounds are not sensitive to the atmosphere, in particular moisture, and show strong visible electroluminescence in the green region of light, they are important emitter materials for use in organic light-emitting devices.

Eco-friendly inorganic molecular novel antiperovskites for light-emitting application

The development of perovskite light-emitting diodes (PeLEDs) has progressed rapidly over the past several years, with high external quantum efficiencies exceeding 20%. However, the deployment of PeLEDs in commercial devices still faces severe challenges, such as environmental pollution, instability and low photoluminescence quantum yields (PLQYs). In this work, we perform high-throughput calculations to exhaustively search the unexplored and eco-friendly novel antiperovskite space (formula: X₃B[MN₄], with octahedron [BX₆] and tetrahedron [MN₄]). The novel antiperovskites have a unique structure whereby a tetrahedron can be embedded into an octahedral skeleton as a light-emitting center causing a space confinement effect, leading to the characteristics of a low-dimensional electronic structure, which then makes these materials potential light-emitting material candidates with a high PLQY and light-emitting stability. Under the guidance of newly derived tolerance, octahedral, and tetrahedral factors, 266 stable candidates are successfully screened out from 6320 compounds. Moreover, the antiperovskite materials Ba₃I_0.5F_0.5(SbS₄), Ca₃O(SnO₄), Ba₃F_0.5I_0.5(InSe₄), Ba₃O_0.5S_0.5(ZrS₄), Ca₃O(TiO₄), and Rb₃Cl_0.5I_0.5(ZnI₄) possess an appropriate bandgap, thermodynamic and kinetic stability, and excellent electronic and optical properties, making them promising light-emitting materials.

Excited-State Dopant-Host Energy-Level Alignment: Toward a Better Understanding of the Photoluminescence Behaviors of Doped Phosphors

Luminescent materials, also known as phosphors, have been widely used for applications such as emissive displays, fluorescent lamps, light-emitting diodes, and X-ray scintillation detectors. The energy-level diagram of a phosphor is extremely important for understanding its photoluminescence behavior. Here, we demonstrate through a combined density functional theory and experimental study that excited-state energy-level alignment accounts for the photoluminescence behaviors much better than ground-state energy-level alignment. An efficient doped phosphor should exhibit a type I excited-state dopant-host energy-level alignment, regardless of whether its ground-state alignment is type I. A type II excited-state dopant-host energy-level alignment implies that exciton dissociation, resulting in photoluminescence quenching. Our results provide not only a better understanding of the photoluminescence behaviors of the reported phosphors but also critical guidance for designing prospective luminescent materials.

Unveiling the Localized Exciton-Based Photoluminescence of Manganese Doped Cesium Zinc Halide Nanocrystals

Lead-free metal halide nanocrystals (NCs) have aroused increasing attention due to their unique optoelectronic properties based on localized excitons (LEs). However, the vital influencing factors for the LEs based photoluminescence (PL) are still not well-understood due to the coupling of various intrinsic and extrinsic factors of the NCs. Herein, by engineering the phase, size, morphology, and chemical composition, we are able to decouple the intrinsic and extrinsic factors of manganese doped cesium zinc-halide NCs. We found both the intrinsic metal-halide coordination field and the extrinsic crystal defects have significant influences on the LEs' recombination and energy transfer processes, and hence determine the PL efficiency. Unlike for the free excitons (FEs) based PL, the phase as well as the crystal morphology do not play major roles for the LEs based PL. This work provides a new insight for the study of LE dynamics of metal halide NCs.

Long-lived spin-triplet excitons in manganese complexes for room-temperature phosphorescence

Low-dimensional metal halide perovskites have become emerging candidates for applications in light emitting diodes due to the quantum confinement effect by tuning their composition and structure. However, they suffer from longstanding issues of environmental stability and lead toxicity. Herein, we report phosphorescent manganese halides, (TEM)₂MnBr₄ (TEM = HN(CH₂CH₃)₃, triethylammonium) and (IM)₆[MnBr₄][MnBr₆] (IM = C₃H₆N₂, imidazolium) with a photoluminescence quantum yield (PLQY) of 50% and 7%, respectively. (TEM)₂MnBr₄ with a tetrahedral configuration exhibits brilliant green light emission centered at 528 nm, while the (IM)₆[MnBr₄][MnBr₆] compound, in which octahedral and tetrahedral units coexist, exhibits red colored emission at 615 nm. The excited state of (TEM)₂MnBr₄ and (IM)₆[MnBr₄][MnBr₆] is found to exhibit distinct photophysical emission characteristics consistent with triplet state phosphorescence. Efficient phosphorescence was achieved with a long lifetime of several milliseconds, 0.38 ms for (TEM)₂MnBr₄ and 5.54 ms for (IM)₆[MnBr₄][MnBr₆], at room temperature. By studying the temperature dependent PL and single-crystal X-ray diffraction measurements and comparing our results with those of previously reported analogues, we have found a direct correlation between Mn⋯Mn distances and PL emission. Our study reveals that the long distance between the Mn centers has made a significant contribution to the long-lived phosphorescence with a highly emissive triplet state.

Luminescence Enhancement of CsMnBr3 Nanocrystals through Heterometallic Doping

The absorption and photoluminescence (PL) of CsMnBr₃ with Mn(II) in octahedral crystal fields are extremely weak due to a d-d forbidden transition. Herein, we introduce a facile and general synthetic procedure that can prepare undoped and heterometallic doped CsMnBr₃ NCs at room temperature. Importantly, both PL and absorption of CsMnBr₃ NCs were significantly improved after doping a small amount of Pb²⁺ (4.9%). The absolute photoluminescence quantum yield (PL QY) of Pb-doped CsMnBr₃ NCs is up to 41.5%, 11-fold higher than undoped CsMnBr₃ NCs (3.7%). The PL enhancement is attributed to the synergistic effects between [MnBr₆]^4- units and [PbBr₆]^4- units. Furthermore, we verified the similar synergistic effects between [MnBr₆]^4- units and [SbBr₆]^4- units in Sb-doped CsMnBr₃ NCs. Our results highlight the potential of tailoring luminescence properties of manganese halides through heterometallic doping.

The Effects of Mono- and Bivalent Linear Alkyl Interlayer Spacers on the Photobehavior of Mn(II)-Based Perovskites

Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime-the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Organic–Inorganic Manganese (II) Halide Hybrid Combining the Two Isomers Cis/Trans of [MnCl4(H2O)2]: Crystal Structure, Physical Properties, Pharmacokinetics and Biological Evaluation

A manganese (II) complex templated by hexahydro-1,4-diazepinediium as a counter ion was grown by slow evaporation from an aqueous solution at room temperature. The X-ray diffraction analysis revealed that the compound (C5H14N2)[MnCl4(H2O)2] crystallizes in the centrosymmetric space group P2/c of the monoclinic system. The crystal structure of the Mn(II) complex is characterized by an alternation of 0-dimensional organic and inorganic stacks linked together by N/O-H…Cl and N-H…O hydrogen bonds, which lead to a three-dimensional supramolecular architecture. In this structure, the inorganic layer is built up by independent anionic moieties combining the two isomers cis/trans of [MnCl4(H2O)2]2−. The thermal decomposition was studied by TGA-DTA techniques. The optical band gap and Urbach energy were obtained by Tauc’s equation. The direct and indirect band gap values are found to be 4.58 and 4.44 eV, respectively. Weak antiferromagnetic interactions are present in the molecule under study, according to magnetic measurements. An agar well diffusion technique was used to assess the synthetic compound’s biological activity, and the results showed that it has potent antibacterial (Gram-positive and Gram-negative) properties. Interestingly, the synthesized compound also displayed antilipase activity. These biological activities have been confirmed by the bioavailability and pharmacokinetic analyses.

Lead-Free Cesium Manganese Halide Nanocrystals Embedded Glasses for X-Ray Imaging

The toxicity of heavy-metal Pb and instability of lead-based halide perovskite nanomaterials are main factors to impede their practical applications in the fields of solar cells, LEDs and scintillators. In this paper, all inorganic lead-free cesium manganese halide nanocrystals are synthesized in glass for the first time. Red photoluminescence with broad PL band, negligible self-absorption and a high photoluminescence quantum yield of 41.8% is obtained. In addition, modulating halide component can change the Mn²⁺ ions coordination environment to obtain tunable photoluminescence from red to green. More importantly, cesium manganese halide nanocrystals embedded glasses exhibit outstanding long-term stabilities. Theses cesium manganese halide nanocrystals embedded glasses are also highly stable against high energy irradiation and exhibit highly efficient radioluminescence, making them promising for high-resolution X-ray imaging. These results demonstrate that cesium manganese halide nanocrystals embedded glasses are promising eco-friendly candidates for applications in light-emitting diodes and scintillators.

Highly Luminescent Earth-Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI₂ (XanPO) crystals showing a notable photoluminescence quantum yield (PLQY) of 94% and a super TQ resistance from 4 to 623 K. This unprecedented superior thermal stability is attributed to the low electron-phonon coupling and the unique rigid crystal structure of MnI₂ (XanPO) over the whole temperature range based on the temperature-dependent photoluminescence (PL) and single crystal X-ray diffraction (SCXRD) analyses. Considering these appealing properties, green PC-LEDs with a power efficacy of 102.5 lm W^-1 , an external quantum efficiency (EQE) of 22.7% and a peak luminance up to 7750 000 cd m^-2 are fabricated by integrating MnI₂ (XanPO) with commercial blue LEDs. Moreover, the applicability of MnI₂ (XanPO) in both micro-LEDs and organic light-emitting diodes (OLEDs) is also demonstrated. In a nutshell, this study uncovers a candidate of highly luminescent and TQ resistant manganese halide suitable for a variety of emission applications.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic-Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides

Organic-inorganic metal halides (OIMHs) have abundant optical properties and potential applications, such as light-emitting diodes, displays, solar cells, and photodetectors. Herein, we report zero-dimensional Mn-based OIMH (C₈H₂₀N)₂MnCl₄ single crystals synthesized by a simple slow evaporation method, which exhibit intense green emission at 520 nm originating from ⁴T₁-⁶A₁ transition of Mn²⁺ ions. Large organic cations in the crystal structure result in the isolated [MnCl₄]^2- tetrahedrons, and the closest Mn-Mn distance reaches 9.07 Å, which effectively inhibits the migration of excitation energy between adjacent Mn²⁺ emission centers, thus achieving a high quantum yield (∼87%) and a long photoluminescence (PL) lifetime (3.42 ms). The different optical and structural properties at low and high temperatures are revealed by temperature-dependent PL and X-ray diffraction spectra. The PL spectra and lifetimes under the heating and cooling processes indicate that the optical property transitions are reversible at 220/240 K. Our work provides a promising strategy for building multifunctional optoelectronic materials and insights into the understanding convertible photophysical properties from isomers of metal halides.

Lead-Free Metal Halide Perovskite Nanocrystals: From Fundamentals to Applications

Lead (Pb) halide perovskite nanocrystals, with the general formula APbX₃ , where A=CH₃ NH³⁺ , CH(NH₂ )²⁺ , or Cs⁺ and X=Cl^- , Br^- , or I^- , have emerged as a class of materials with promising properties due to their remarkable optical properties and solar cell performance. However, important issues still need to be addressed to enable practical applications of these materials, such as instability, mass production, and Pb toxicity. Recent studies have carried out the replacement of Pb by various less-toxic cations as Sn, Ge, Sb, and Bi. This variety of chemical compositions provide Pb-free perovskite and metal halide nanostructures with a wide spectral range, in addition to being considered less toxic, therefore having greater practical applicability. Highlighting the necessity to address and solve the toxicity problems related to Pb-containing perovskite, this review considers the prospects of the Pb-free perovskite, involving synthesis methods, and properties of them, including advantages, disadvantages, and applications.

Highly Efficient, Flexible, and Eco-Friendly Manganese(II) Halide Nanocrystal Membrane with Low Light Scattering for High-Resolution X-ray Imaging

Scintillators enable invisible X-ray to be converted into ultraviolet (UV)/visible light that can be collected using a sensor array and is the core component of the X-ray imaging system. However, combining the excellent properties of high light output, high spatial resolution, flexibility, non-toxicity, and cost effectiveness into a single X-ray scintillator remains a great challenge. Herein, a novel scintillator based on benzyltriphenylphosphonium manganese(II) bromide (BTP₂MnBr₄) nanocrystal (NC) membranes was developed by the in situ fabrication strategy. The long Mn-Mn distance provided by the large BTP cation allows the nonradiative energy dissipation in this manganese(II) halide to be significantly suppressed. As a result, the flexible BTP₂MnBr₄ NC scintillator shows an excellent linear response to the X-ray dose rate, a high light yield of ∼71,000 photon/MeV, a low detection limit of 86.2 nGy_air/s at a signal-to-noise ratio of 3, a strong radiation hardness, and a long-term thermal stability. Thanks to the low Rayleigh scattering associated with the dense distribution of nanometer-scale emitters, light cross-talk in X-ray imaging is greatly suppressed. The impressively high-spatial resolution X-ray imaging (23.8 lp/mm at modulation transfer function = 0.2 and >20 lp/mm for a standard pattern chart) was achieved on this scintillator. Moreover, well-resolved 3D dynamic rendering X-ray projections were also successfully demonstrated using this scintillator. These results shed light on designing efficient, flexible, and eco-friendly scintillators for high-resolution X-ray imaging.

Large-Area Laminar TEA2MnI4 Single-Crystal Scintillator for X-ray Imaging with Impressive High Resolution

Current X-ray imaging scintillators are dominated by inorganic scintillators grown through a high-temperature process. Exploring new types of scintillators with mild growth conditions, high light yields, and eco-friendly chemical compositions is essential and challenging. Herein, the zero-dimensional large-area laminar organic-inorganic hybrid metal halide TEA₂MnI₄ (TEA = tetraethylammonium) single crystal with dimensions of 50 mm × 60 mm × 0.82 mm is grown via a local-heating solvent evaporation method. Compared with its Cl- and Br-based counterparts, the incorporation of the iodine component enhances the X-ray attenuation ability and significantly accelerates the decay of the photoluminescence of TEA₂MnI₄. Interestingly, the prepared TEA₂MnI₄ exhibits a high transmittance of >90% over the range of 515-765 nm and exhibits a high light yield of 26288 photons/MeV, which provides the prerequisite for high-resolution X-ray imaging. The TEA₂MnI₄ single-crystal scintillator displays an astonishing spatial resolution exceeding 25 line pairs per millimeter, which provides a design concept for a Mn-I-based single crystal for high-performance scintillator applications.

Ultrasensitive Optical Thermometry via Inhibiting the Energy Transfer in Zero-Dimensional Lead-Free Metal Halide Single Crystals

Self-referencing optical thermometry based on the fluorescence intensity ratio (FIR) have drawn extensive attention as a result of their high sensitivity and non-invasively fast response to temperature. However, it is a great challenge for luminescent materials to achieve simultaneously high absolute and relative temperature sensitivity based on the FIR technique. Herein, we developed a novel optical thermometer by designing hybrid lead-free metal halide (TTPhP)₂MnCl₄:Sb³⁺ (TTPhP⁺ = tetraphenylphosphonium cation) single crystals with multimodal photoluminescence (PL). The large TTPhP⁺ organic chain resulted in isolated [MnCl₄]^2- and [SbCl₅]^2- in the single crystal, which leads to a negligible energy trasfer process within them. Therefore, the two PL bands (band 1 from [MnCl₄]^2-) with a peak at 518 nm and band 2 (from [SbCl₅]²) with a peak at 640 nm exhibit different thermal-quenching effects, which resulted in excellent temperature sensitivity, with the maximum absolute and relative sensitivities reaching 0.236 K^-1 and 3.77% K^-1 in a temperature range from 300 to 400 K. Both the absolute and relative sensitivities are among the highest values for luminescence thermometry.

Cu+ → Mn2+ Energy Transfer in Cu, Mn Coalloyed Cs3ZnCl5 Colloidal Nanocrystals

In this work, we report the hot-injection synthesis of Cs₃ZnCl₅ colloidal nanocrystals (NCs) with tunable amounts of Cu⁺ and Mn²⁺ substituent cations. All the samples had a rodlike morphology, with a diameter of ∼14 nm and a length of ∼30-100 nm. Alloying did not alter the crystal structure of the host Cs₃ZnCl₅ NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies. The spectroscopic analysis of unalloyed, Cu-alloyed, Mn-alloyed, and Cu, Mn coalloyed NCs indicated that (i) the Cs₃ZnCl₅ NCs have a large band gap of ∼5.35 eV; (ii) Cu(I) aliovalent alloying leads to an absorption shoulder/peak at ∼4.8 eV and cyan photoluminescence (PL) peaked at 2.50 eV; (iii) Mn(II) isovalent alloying leads to weak Mn PL, which intensifies remarkably in the coalloyed samples, prompted by an energy transfer (ET) process between the Cu and Mn centers, favored by the overlap between the lowest (⁶A₁ → ⁴T₁) transition for tetrahedrally coordinated Mn²⁺ and the PL profile from Cu(I) species in the Cs₃ZnCl₅ NCs. The efficiency of this ET process reaches a value of 61% for the sample with the highest extent of Mn alloying. The PL quantum yield (QY) values in these Cu, Mn coalloyed NCs are lower at higher Mn contents. The analysis of the Mn PL dynamics in these samples indicates that this PL drop stems from inter-Mn exciton migration, which increases the likelihood of trapping in defect sites, in agreement with previous studies.

Improving the Chemical Stability of Narrow-Band Green-Emitting Manganese(II) Hybrid by Zn-Doping

Hybrid tetrahedral Mn(II)-based halides show great potential for narrow-band green emitters, which could be applied in the liquid crystal display field. However, the strategy to improve the chemical stability of tetrahedral Mn hybrids has not been fully investigated. Here, we demonstrate that Zn doping can be an effective route to significantly improve the stability of tetrahedral Mn hybrids under air conditions without compromising the luminous efficiency. A new bromide (ABI)₂MnBr₄ (ABI = 2-aminobenzimidazole) is synthesized, which exhibits a typical zero-dimensional structure with isolated [MnBr₄]^2- tetrahedra in the P1̅ space group. Under 450 nm excitation, a narrow-band green-emitting peak at 516 nm is observed with a full width at half maximum of 42 nm. It is indicated that spontaneous phase transition from the tetrahedral to octahedral motif occurs in this Mn hybrid driven by humidity, combined with the emission color change from green to red. Interestingly, this phase transition could be strongly suppressed by Zn doping with a very low doping amount (5%), leading to the significantly improved chemical stability of (ABI)₂MnBr₄ without reducing the photoluminescence quantum yield. Our work provides a simple and feasible strategy to enhance the chemical stability of the green-emitting (ABI)₂MnBr₄, and it may also be applicable for other tetrahedral Mn-based hybrids.

Ligand Engineering Triggered Efficiency Tunable Emission in Zero-Dimensional Manganese Hybrids for White Light-Emitting Diodes

Zero-dimensional (0D) hybrid manganese halides have emerged as promising platforms for the white light-emitting diodes (w-LEDs) owing to their excellent optical properties. Necessary for researching on the structure-activity relationship of photoluminescence (PL), the novel manganese bromides (C₁₃H₁₄N)₂MnBr₄ and (C₁₃H₂₆N)₂MnBr₄ are reported by screening two ligands with similar atomic arrangements but various steric configurations. It is found that (C₁₃H₁₄N)₂MnBr₄ with planar configuration tends to promote a stronger electron-phonon coupling, crystal filed effect and concentration-quenching effect than (C₁₃H₂₆N)₂MnBr₄ with chair configuration, resulting in the broadband emission (FWHM = 63 nm) to peak at 539 nm with a large Stokes shift (70 nm) and a relatively low photoluminescence quantum yield (PLQY) (46.23%), which makes for the potential application (LED-1, Ra = 82.1) in solid-state lighting. In contrast, (C₁₃H₂₆N)₂MnBr₄ exhibits a narrowband emission (FWHM = 44 nm) which peaked at 515 nm with a small Stokes shift (47 nm) and a high PLQY of 64.60%, and the as-fabricated white LED-2 reaches a wide colour gamut of 107.8% National Television Standards Committee (NTSC), thus highlighting the immeasurable application prospects in solid-state display. This work clarifies the significance of the spatial configuration of organic cations in hybrids perovskites and enriches the design ideas for function-oriented low-dimensional emitters.

A Red-Emitting Hybrid Manganese Halide Perovskite C5H5NOMnCl2·H2O Featuring One-Dimensional Octahedron Chains

Herein, we successfully synthesized a new organic-inorganic hybrid manganese halide perovskite C₅H₅NOMnCl₂·H₂O, in which organic molecules, water molecules (through O atoms), and Cl atoms coordinate with Mn atoms to form deformed [MnO₃Cl₃] octahedrons. Then, octahedrons form a chain through edge sharing, resulting in a 1D-chain single crystal structure. The high-quality C₅H₅NOMnCl₂·H₂O single crystal prepared by a simple solvent evaporation method produced bright red emission at 656 nm attributed to the d-d transition of Mn²⁺. Also, it has a photoluminescence quantum yield (PLQY) of 24.2%. Photoluminescence excitation and absorption spectra were both featured with multiple bands and were in good agreement with the Mn²⁺ 3d energy levels. The photoluminescence decay spectrum showed an average lifetime of 0.466 ms, which further proves the d-d transition mechanism. The C₅H₅NOMnCl₂·H₂O single crystal had a direct band gap of 1.43 eV. Moreover, a red light LED with a CCT of 1857 K was obtained based on the C₅H₅NOMnCl₂·H₂O powder, indicating its promising application in red-emitting LED.

Synthesis of Cs3MnBr5 Green Phosphors Using an Eco-Friendly Evaporative Crystallization Process

Green (G) and red (R) light-emitting materials, such as quantum dots, perovskite nanocrystals, and inorganic phosphor powders, owing to their excellent optical characteristics, have attracted researchers' attention as color-conversion materials for lighting and display applications. However, these materials contain environmentally harmful elements, such as Pb or Cd, and/or they are synthesized using environmentally harmful synthetic approaches and conditions, involving the use of organic solvents, high pressure, high temperature, harsh atmosphere, and long reaction time. In this study, as an eco-friendly synthetic approach to synthesize lead-free Cs₃MnBr₅ G powder phosphor, we suggest an evaporative crystallization process of aqueous reactant solution. This synthetic process does not use toxic elements or solvents and the crystallization process utilizes only low reaction temperature and short reaction time under air atmosphere conditions. We successfully synthesized Cs₃MnBr₅ green powder phosphor, with excellent optical properties, by evaporative heating of a 200 nm syringe-filtered solution at 150 °C for 2 h. The synthesized Cs₃MnBr₅ phosphors have a photoluminescence quantum yield of 66.3%, a peak wavelength of 520 nm, a narrow bandwidth of 38 nm, and a photoluminescence decay time of 0.34 ms under blue excitation. This phosphor is expected to be a useful alternative G-emitting material that can compete with commercial green quantum dots, perovskite nanocrystals, or inorganic phosphors.

Structural Origin of Enhanced Circularly Polarized Luminescence in Hybrid Manganese Bromides

Chiral hybrid metal halides with a high dissymmetry factor (g_lum ) and a superior photoluminescence quantum yield (PLQY) are promising candidates for circularly polarized luminescence (CPL) light sources. Here, we report eight new chiral hybrid manganese halides, crystallizing in the non-centrosymmetric space group P2₁ 2₁ 2₁ and showing intense CPL emissions. Oppositely-signed circular dichroism (CD) and CPL signals are detected according to the R- and S-configurations of the chiral alkanolammonium cations. Time-resolved PL spectra show long averaged decay lifetimes up to 1 ms for (R-3-quinuclidinol)MnBr₃ (R-1). The g_lum of polycrystalline samples for coordinated structures (23×10^-3 ) is more than doubled compared with the non-coordinated ones (8.5×10^-3 ), due to the structural variations. R-1 exhibit both a high g_lum and a high PLQY (50.2 %). The effective chirality transfer mechanism through coordination bonds, with strongly emissive Mn^II centers, enables a new class of high-performance CPL materials.

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.

Organic Cation Modulation Triggered Second Harmonic Response in Manganese Halides with Bright Fluorescence

Zero-dimensional (0D) hybrid manganese halides have been recently synthesized and exhibited rich functional properties including fluorescence, ferroelectrics, and ferromagnetism. However, few studies on second-harmonic generation (SHG) behaviors of manganese halide crystals have been reported, presumably owing to the d-d transitions. Here, we report three manganese bromides, [TEA]₂MnBr₄ (TEA⁺ = tetraethylammonium; 1), [BTEA]₂MnBr₄ (BTEA⁺ = benzyltriethylammonium; 2), and [BTMA]₂MnBr₄ (BTMA⁺= benzyltrimethylammonium; 3), with linear and nonlinear optical properties via benzyl or ethyl/methyl substitution strategies. They feature 0D structures containing isolated [MnBr₄]^2- anions and quaternary ammonium cations with different sizes inserted for charge balance. They all show green phosphorescence, and 2 possesses good luminescence efficiency with a quantum yield of 97.8%, which is larger than those of 1 (79%) and 3 (72%). Specifically, acentric 1 and 3 present effective SHG responses about 0.48 and 0.59 times that of KDP, respectively. The result throws light on the new properties of the hybrid manganese halides and provides a new way to develop novel nonlinear optical-active organic-inorganic hybrid metal halides.

Zero-Dimensional (Piperidinium)2MnBr4: Ring Puckering-Induced Isostructural Transition and Strong Electron-Phonon Coupling-Mediated Self-Trapped Exciton Emission

We report on the synthesis, structure, and photophysical properties of a lead-free organic-inorganic hybrid halide, (Piperidinium)₂MnBr₄ (PipMBr). It crystallizes in a monoclinic P2₁/n structure, with isolated MnBr₄ tetrahedra representing a zero-dimensional compound. It undergoes a reversible isostructural transition at 422/417 K in the heating/cooling cycle owing to the hydrogen-bonding rearrangement mediated by ring puckering of piperidinium cations. This compound exhibits green emission with a photoluminescence quantum yield of 51%. Interestingly, strong electron-longitudinal optical phonon coupling with γ_LO of 237 meV is evidenced from the broadening of the temperature-dependent emission linewidth and the Raman spectrum. Such strong electron-phonon coupling and a relatively low Debye temperature (137 K) suggest the self-trapped exciton emission in this compound.