A core-shell model of polymetallic hybrid metal halides

Most polymetallic hybrid metal halides are assumed to show a homogenous distribution of the metal ions in the bulk. Herein, we demonstrate a core-shell model for the hybrid lead halide [(C6H18N3)2·Pb2Br10] (C6H18N3 = 2-(piperazin-1-yl)ethan-1-aminium) coated with a manganese bromide layer. This model can explain the different photoemission of this composite material, and provides new insights on the investigation of polymetallic low-dimensional organic metal halides.

The developments of cyan emitting phosphors to fulfill the cyan emission gap of white-LEDs

Future generations of solid-state lighting (SSL) will prioritize the development of innovative luminescent materials with superior characteristics. The phosphors converted into white light-emitting diodes (white LEDs) often have a blue-green cavity. Cyan-emitting phosphor fills the spectral gap and produces "full-visible-spectrum lighting." Full-visible spectrum lighting is beneficial for several purposes, such as light therapy, plant growth, and promoting an active and healthy lifestyle. The design of cyan garnet-type phosphors, like Ca2LuHf2Al3O12 (CLHAO), has recently been the subject of interest. This review study reports a useful cyan-emitting phosphor based on CLHAO composition with a garnet structure to have a cyan-to-green emitting color with good energy transfer. It could be employed as cyan filler in warm-white LED manufacturing. Due to its stability, ability to dope with various ions suitable for their desired qualities, and ease of synthesis, this garnet-like compound is a great host material for rare-earth ions. The development of CLHAO cyan-emitting phosphors has exceptionally high luminescence, resulting in high CRI and warm-white LEDs, making them a viable desire for LED manufacturing. The development of CLHAO cyan-emitting phosphors with diverse synthesis techniques, along with their properties and applications in white LEDs, are extensively covered in this review paper.

Achieving Tunable Cold/Warm White-Light Emission in a Single Perovskite Material with Near-Unity Photoluminescence Quantum Yield

Single materials that exhibit efficient and stable white-light emission are highly desirable for lighting applications. This paper reports a novel zero-dimensional perovskite, Rb4CdCl6:Sn2+, Mn2+, which demonstrates exceptional white-light properties including adjustable correlated color temperature, high color rendering index of up to 85, and near-unity photoluminescence quantum yield of 99%. Using a co-doping strategy involving Sn2+ and Mn2+, cyan-orange dual-band emission with complementary spectral ranges is activated by the self-trapped excitons and d-d transitions of the Sn2+ and Mn2+ centers in the Rb4CdCl6 host, respectively. Intriguingly, although Mn2+ ions doped in Rb4CdCl6 are difficult to excite, efficient Mn2+ emission can be realized through an ultra-high-efficient energy transfer between Sn2+ and Mn2+ via the formation of adjacent exchange-coupled Sn-Mn pairs. Benefiting from this efficient Dexter energy transfer process, the dual emission shares the same optimal excitation wavelengths of the Sn2+ centers and suppresses the non-radiative vibration relaxation significantly. Moreover, the relative intensities of the dual-emission components can be modulated flexibly by adjusting the fraction of the Sn2+ ions to the Sn-Mn pairs. This co-doping approach involving short-range energy transfer represents a promising avenue for achieving high-quality white light within a single material.

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.

Insight into efficient photoluminescence regulation mechanism by lattice distortion and Mn2+ doping in organic-inorganic hybrid perovskites

The space configurations of organic ammonium cations play a vital role in indirectly revealing the relationship between the structures and photoluminescence properties. Structural transformation induced tunability of the photophysical properties has rarely been reported. In this work, two organic-inorganic halide perovskites with different octahedral distortions were synthesized to explore the relationships between "steric effect" of organic cations and photoluminescence properties. The broadband emission of (DETA)PbBr₅·H₂O with high octahedral distortion is attributed to self-trapped excitons and trap states, whereas smaller steric hindrance ammonium cation 1,4-butanediamine form a 2D layered perovskite with narrowband emission due to free excitons. More importantly, the photoactive metal ions Mn²⁺ doping strategy gives rise to tunable broadband light emission from weak to strong orange emission with higher PLQY up to 20.96 % and 12.90% in 0D (DETA)Pb_0.2Mn_0.8Br₅·H₂O and 2D (BDA)Pb_0.8Mn_0.2Br₄ respectively. Combined with time-correlated single photon counting and photoluminescence spectra, Mn-doped perovskites reveal energy transfer from host to Mn²⁺ characteristic energy level (⁴T₁-⁶A₁). Importantly, defect states are reduced by doping manganese ions in (DETA)PbBr₅·H₂O to enhance photoluminescence intensity. This work sheds light on the mechanism of defect-related emission and provides a successful strategy for designing novel and adjustable materials.

Introduction of Multicomponent Dyes into 2D MOFs: A Strategy to Fabricate White Light-Emitting MOF Composite Nanosheets

Metal-organic frameworks (MOFs) have been extensively studied in host-guest chemistry by means of ultrahigh porosities, tunable channels, and component diversities. As the host matrix, MOFs exhibit immense potential in the preparation of single-phase white light-emitting (SPWLE) materials. Nonetheless, it is a great challenge that the size of the introduced guest molecules is limited by MOF pores, which affects the WLE optimization. In this work, two-dimensional (2D) MOFs are first utilized as the host matrices to simultaneously encapsulate red-green-blue fluorescent dyes for SPWLE. Various dyes@2D MOF composites with high-quality WLE performances and ultrathin nanosheet morphologies are directly assembled from 2D MOF precursors and dyes in high yields. Owing to the flexible interlamellar space of 2D MOFs, different types and sizes of guests can be easily introduced, which greatly expands the range of available MOF hosts and guests, making the WLE much more tunable. The strategy of employing 2D MOFs as the host matrices to introduce multicomponent dyes for SPWLE nanosheets resolves the restriction of MOF pores on the guest molecule size and opens a new avenue to rationally design and prepare SPWLE nanosheets that are highly solution-processable.

High-Efficiency Intrinsic Yellow-Orange Emission in Hybrid Indium Bromide with Double Octahedral Configuration

Zero-dimensional (0D) In-based organic-inorganic metal halides (OIMHs) have received growing interest in recent years as promising luminescent materials. However, the high efficiencies of 0D In-based OIMHs are all dependent on Sb doping in the existing literature. Here, we report a novel 0D In-based OIMH (C₁₀H₂₂N₂)₂In₂Br₁₀, which exhibits intrinsic broadband emission (610 nm), and the photoluminescence quantum yield (PLQY) can reach 70% without Sb doping. (C₁₀H₂₂N₂)₂In₂Br₁₀ shows a typical 0D structure with three different In-Br polyhedra (two octahedra and one tetrahedron) separated by large organic cations. Based on the optical property measurements and theoretical calculations, we demonstrate that (C₁₀H₂₂N₂)₂In₂Br₁₀ is an indirect semiconductor with a band gap of 3.74 eV, and the In-Br inorganic moiety is primarily responsible for the intense emission of (C₁₀H₂₂N₂)₂In₂Br₁₀. Interestingly, the unique double octahedral configuration in (C₁₀H₂₂N₂)₂In₂Br₁₀ may enhance the structural distortion and stimulate the self-trapped excitons (STEs), leading to the related high PLQY. Our work provides a novel 0D In-based OIMH with high-efficiency intrinsic emission, which is helpful for understanding the structure-PL relationships of hybrid halides.

Self-trapped excitons in soft semiconductors

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

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

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

Zero-Dimensional Hybrid Indium Halides with Efficient and Tunable White-Light Emissions

Two-dimensional hybrid lead perovskites have attracted a great deal of attention in white-light-emitting diodes, but the serious toxicity of Pb²⁺ and the limited photoluminescence quantum yield (PLQY) still restrict further optoelectronic application. To address these issues, a new combining photon strategy was proposed to achieve highly efficient broadband white-light emission in a new family of zero-dimensional (0D) indium halides based on an [InCl₆]^3- octahedron. Remarkably, these 0D halides display dual-band white-light emission derived from the synergistic work of blue- and yellow-light-emitting bands, which can be ascribed to the radiative recombination of bound excitons in organic cations and self-trapped excitons in inorganic anions, respectively, based on spectroscopy and theoretical studies. In-depth first-principles calculation demonstrates that the increased structural deformability effectively improves the PLQY from 7.01% to 18.56%. As a proof of concept, this work provides a profound understanding for advancing the rational design of novel single-component 0D lead-free halides as high-performance white-light emitters.

Modeling bismuth insertion in 1D hybrid lead halide TMSO(PbxBiy)I3pseudo-perovskites

The structures of the disordered 1D (pseudo-)perovskites of general TMSO(Pb_xBi_y)I₃formulation [TMSO = (CH₃)₃SO⁺], obtained by doping the TMSOPbI₃species with Bi³⁺ions, are investigated through the formulation of a statistical model of correlated disorder, which addresses the sequences of differently occupied BI₆face-sharing octahedra (B = Pb, Bi or vacant site) within ideally infinite [(BI₃)^-]_nchains. The x-ray diffraction patterns simulated on the basis of the model are matched to the experimental traces, which show many broad peaks with awkward (nearly trapezoidal) shapes, under the assumption that the charge balance is fully accomplished within each chain. The analysis allowed to establish a definite tendency of the metal species to cluster as pure Pb and Bi sequences. The application of the model is discussed critically, in particular as what concerns the possibility that further B-site neighbors beyond the second may influence the overall B-site occupancies.

Efficient Yellow Self-Trapped Exciton Emission in Sb3+-Doped RbCdCl3 Metal Halides

Metal halide perovskites have flexible crystal and electronic structures and adjustable emission characteristics, which have very broad applications in the optoelectronic field. Among them, all-inorganic perovskites have attracted more attention than others in recent years because of their characteristics of large diffusion length, high luminescence efficiency, and good stability. In this work, Sb³⁺-doped RbCdCl₃ crystalline powder was synthesized by a simple hydrothermal method, and its luminescence properties were studied, which showed a broad emission band with a large Stokes shift and efficient yellow light emission at about 596 nm at room temperature with a photoluminescence quantum yield of 91.7%. The emission came from the transition of the self-trapped exciton 1 (STE1) out of ³P_n (n = 0, 1, and 2) to S₀ due to strong electron-phonon coupling, which scaled with increasing temperature. Moreover, its emission color became white at low temperatures due to the occurrence of transition of other self-trapped exciton 0 (STE0) state emission out of the ¹S states of Sb ions to S₀ in the lattice. These emission color changes may be used for temperature sensing, and this Sb³⁺-doped RbCdCl₃ material expands the knowledge of the efficient luminescent inorganic material family for further applications of all-inorganic perovskites.

Mn2+-activated dual-wavelength emitting materials toward wearable optical fibre temperature sensor

Photothermal sensing is crucial for the creation of smart wearable devices. However, the discovery of luminescent materials with suitable dual-wavelength emissions is a great challenge for the construction of stable wearable optical fibre temperature sensors. Benefiting from the Mn²⁺-Mn²⁺ superexchange interactions, a dual-wavelength (530/650 nm)-emitting material Li₂ZnSiO₄:Mn²⁺ is presented via simple increasing the Mn²⁺ concentration, wherein the two emission bands have different temperature-dependent emission behaviours, but exhibit quite similar excitation spectra. Density functional theory calculations, coupled with extended X-ray absorption fine structure and electron-diffraction analyses reveal the origins of the two emission bands in this material. A wearable optical temperature sensor is fabricated by incorporating Li₂ZnSiO₄:Mn²⁺ in stretchable elastomer-based optical fibres, which can provide thermal-sensitive emissions at dual- wavelengths for stable ratiometric temperature sensing with good precision and repeatability. More importantly, a wearable mask integrated with this stretchable fibre sensor is demonstrated for the detection of physiological thermal changes, showing great potential for use as a wearable health monitor. This study also provides a framework for creating transition-metal-activated luminescence materials.

Dual-wavelength emission materials can provide fluorescence intensity ratio technology with self-calibration features; their fabrication however, remains a challenge. Here, authors design a dual-wavelength emitting material Li₂ZnSiO₄:Mn²⁺ and present a wearable optical fibre temperature sensor, functioning in both contact and noncontact modes.

Tailoring Photophysical Dynamics in a Hybrid Gallium-Bismuth Heterometallic Halide by Transferring from an Indirect to a Direct Band Structure

Low-dimensional lead-free metal halides have emerged as novel luminous materials for solid-state lighting, remote thermal imaging, X-ray scintillation, and anticounterfeiting labeling applications. However, the influence of band structure on the intriguing optical property has rarely been explored, especially for low-dimensional hybrid heterometallic halides. In this study, we have developed a lead-free zero-dimensional gallium-bismuth hybrid heterometallic halide, A₈(GaCl₄)₄(BiCl₆)₄ (A = C₈H₂₂N₂), that is photoluminescence (PL)-inert because of its indirect-band-gap character. Upon rational composition engineering, parity-forbidden transitions associated with the indirect band gap have been broken by replacing partial Ga³⁺ with Sb³⁺, which contains an active outer-shell 5s² lone pair, resulting in a transition from an indirect to a direct band gap. As a result, broadband yellow PL centered at 580 nm with a large Stokes shift over 200 nm is recorded. Such an emission is attributed to the radiative recombination of an allowed direct transition from triplet ³P₁ states of Sb³⁺ based on experimental characterizations and theoretical calculations. This study provides not only important insights into the effect of the band structure on the photophysical properties but a guidance for the design of new hybrid heterometallic halides for optoelectronic applications.

Antimony -doped indium-based halide single crystals enabling white-light emission

Metal halides (TMPL)3InCl6·EtOH:xSb3+ with tunable colors were obtained by gradient Sb3+ doping. Interestingly, white emission was achieved when 0.1% of Sb3+ was employed, due to a combination of the cyan emission of organic moiety and orange emission from metal halides.

Water-Molecule-Induced Emission Transformation of Zero-Dimension Antimony-Based Metal Halide

Low-dimensional organic-inorganic metal halides have recently emerged as a class of promising luminescent materials. However, the intrinsic toxicity of lead would strongly hamper future application. Herein, we synthesized a new type of lead-free zero-dimensional (0D) antimony-based organic-inorganic metal halide single crystals, (PPZ)₂SbCl₇·5H₂O (PPZ = 1-phenylpiperazine), which features a broadband emission at 720 nm. Ultrafast transient absorption and temperature-dependent photoluminescence (PL) spectra are combined to investigate the PL mechanism, revealing that self-trapped exciton recombination was involved. Furthermore, it is interesting that (PPZ)₂SbCl₇·5H₂O material shows reversible PL emission transformation between red light (720 nm) and yellow light (590 nm) as water molecules are inserted or removed from the lattice. Such reversible emission transformation phenomenon renders the (PPZ)₂SbCl₇·5H₂O as a potential low-cost water sensing material.

Composition and Antithermal Quenching of Noninteger Stoichiometric Eu2+-Doped Na-β-Alumina with Cyan Emission for Near-UV WLEDs

Phosphors with high quantum efficiency and thermal stability play a key role in improving the performance of phosphor-converted white light-emitting diodes (pc-WLEDs). A near-UV-pumped LED shows a great advantage due to its reduction of the negative effect of blue light on human health. In this work, we propose a series of near-UV excitable cyan-emitting Eu²⁺-activated phosphors with a nominal composition of Na_2-2xAl₁₁O_17+a:xEu²⁺ (x = 0.01-0.40), which crystallize in a sodium β-alumina phase with a composition close to Na_1.22Al₁₁O_17.11. An excess amount of the sodium carbonate raw material makes up the volatile Na during the high-temperature process. The noninteger stoichiometric composition promotes the rigidity of the crystal structure with a slight excess of Na insertion into layers between spinel blocks of the NaAl₁₁O₁₇ matrix. The nonequivalent substitution of Na⁺ by Eu²⁺ generates intrinsic defects acting as carrier traps. As a result, the phosphor with an optimal nominal composition Na_1.6Al₁₁O_17+a:0.20Eu²⁺, under the excitation at 365 nm, shows an asymmetric cyan emission band at 468 nm with internal and external quantum efficiencies of 81.3 and 56.9%, respectively. Remarkably, the phosphor exhibits antithermal quenching within 200 °C. A pc-WLED with a high color rendering index (87.2) suggests great potential of the phosphor in pc-WLEDs. Therefore, a combination of a rigid structure and deep trap level is an effective way in exploring new phosphors with high quantum efficiency and thermal stability.

Bulk Mn2+ Doped 1D Hybrid Lead Halide Perovskite with Highly Efficient, Tunable and Stable Broadband Light Emissions

Mn²⁺ doped colloidal three-dimensional (3D) lead halide perovskite nanocrystal (PNC) has attracted intensive research attention; however, the low exciton binding energy and fatal optical instability of 3D PNC seriously hinder the optoelectronic application. Therefore, it remains significant to explore new stable host perovskite with strongly bound exciton to realize more desirable luminescent property. In this work, we utilized bulk one-dimensional (1D) hybrid perovskite of [AEP]PbBr₅  ⋅ H₂ O (AEP=N-aminoethylpiperazine) as structural platform to rationally optimize the luminescent property by a controllable Mn²⁺ doping strategy. Significantly, the series of Mn²⁺ -doped 1D [AEP]PbBr₅  ⋅ H₂ O show enhanced energy transfer efficiency from the strongly bound excitons of host material to 3d electrons of Mn²⁺ ions, resulting in tunable broadband light emissions from weak yellow to strong red spectral range with highest photoluminescence quantum yield up to 28.41 %. More importantly, these Mn²⁺ -doped 1D perovskites display ultrahigh structural and optical stabilities in humid atmosphere, water and high temperature exceeding the conventional 3D PNC. Combined highly efficient, tunable and stable broadband light emissions enable Mn²⁺ -doped 1D perovskite as excellent down-converting phosphor showcasing the potential application in white light emitting diode. This work not only provides a profound understanding of low-dimensional perovskites but also opens a new way to rationally design high-performance broadband light emitting perovskites for solid-state lighting and displaying devices.

Multiexcitonic Emission in Zero-Dimensional Cs2ZrCl6:Sb3+ Perovskite Crystals

Metal halide perovskites are highly attractive for lighting applications, but the multiexcitonic emission processes in these crystals are largely unexplored. This study presents an investigation of Sb³⁺-doped Cs₂ZrCl₆ perovskite crystals that display double luminescence due to the intrinsic host self-trapped excitons (denoted as host STEs) and dopant-induced extrinsic self-trapped excitons (denoted as dopant STEs), respectively. Steady-state and transient-state spectroscopy reveal that the host and dopant STEs can be independently charged at specific energies. Density functional theory calculations confirm that the multiexcitonic emission stems from minimal interactions between the host and dopant STEs in the zero-dimensional crystal lattice. By selective excitation of different STEs through precise control of excitation wavelength, we further demonstrate dynamic color tuning in the Cs₂ZrCl₆:Sb³⁺ crystals. The color kinetic feature offers exciting opportunities for constructing multicolor light-emitting devices and encrypting multilevel optical codes.

A One-Dimensional Broadband Emissive Hybrid Lead Iodide with Face-Sharing PbI6 Octahedral Chains

One-dimensional (1D) organic-inorganic hybrid lead halides with unique core-shell quantum wire structures and splendid photoluminescence properties have been considered one of the most promising high-efficiency broadband emitters. However, studies on the broadband emissions in 1D purely face-shared lead iodide hybrids are still rare so far. Herein, we report on a new 1D lead iodide hybrid, (2cepyH)PbI₃ (2cepy = 1-(2-chloroethyl)pyrrolidine), characterized with face-sharing PbI₆ octahedral chains. Upon UV photoexcitation, this material shows broadband yellow emissions originating from the self-trapped excitons associated with distorted Pb-I lattices on account of the strong exciton-phonon coupling, as proved by variable-temperature emission spectra. Moreover, experimental and calculated results reveal that (2cepyH)PbI₃ is an indirect bandgap semiconductor, the band structures of which are governed by inorganic parts. Our work represents the first broadband emitter based on a 1D face-shared lead iodide hybrid and opens a new way to obtain the novel broadband emission materials.

Indium-antimony-halide single crystals for high-efficiency white-light emission and anti-counterfeiting

Although single-source white emissive perovskite has emerged as a class of encouraging light-emitting material, the synthesis of lead-free halide perovskite materials with high luminous efficiency is still challenging. Here, we report a series of zero-dimensional indium-antimony (In/Sb) alloyed halide single crystals, BAPPIn_2-2x Sb_2x Cl₁₀ (BAPP = C₁₀H₂₈N₄, x = 0 to 1), with tunable emission. In BAPPIn_1.996Sb_0.004Cl₁₀, bright yellow emission with near 100% photoluminescence quantum yield (PLQY) is yielded when it was excited at 320 nm, which turns into bright white-light emission with a PLQY of 44.0% when excited at 365 nm. Combined spectroscopy and theoretical studies reveal that the BAPP⁴⁺-associated blue emission and inorganic polyhedron-afforded orange emission function as a perfect pair of complementary colors affording white light in BAPPIn_1.996Sb_0.004Cl₁₀ Moreover, the interesting afterglow behavior, together with excitation-dependent emission property, makes BAPPIn_2-2x Sb_2x Cl₁₀ as high-performance anti-counterfeiting/information storage materials.

Tailoring of White Luminescence in a NaLi3 SiO4 :Eu2+ Phosphor Containing Broad-Band Defect-Induced Charge-Transfer Emission

Single-component materials with white-light emission are ideal for lighting applications. However, it is very challenging to achieve white luminescence in single-dopant activated solid phosphors. Herein, white NaLi₃ Si_{1- x} O₄ :Eu²⁺ materials are designed via defect engineering and synthesized by reducing the Si content (0.15 ≤ x ≤ 0.25). Stochiometric NaLi₃ SiO₄ :Eu²⁺ exhibits a narrow-band blue emission at 469 nm, ascribed to the 5d → 4f transition of Eu²⁺ at highly symmetric cuboid Na sites, while samples with Si content reduced by 15-25% display white emission with two peaks at 472 nm and 585 nm. The newly appeared broadband yellow peak arises from charge-transfer transitions involving Eu²⁺ and nearby defects, as verified by an unusual bandwidth, a large Stokes shift, and a long decay time. A single-component white light-emitting diode device is fabricated by employing a white phosphor to demonstrate a color-rendering index of 82.9. This result provides a new design strategy for single-component white-light materials with broad-band defect-induced charge-transfer emission.

Efficiency-Tunable Single-Component White-Light Emission Realized in Hybrid Halides Through Metal Co-Occupation

Organic-inorganic hybrid metal halides have attracted widespread attention as emerging optoelectronic materials, especially in solid-state lighting, where they can be used as single-component white-light phosphors for white light-emitting diodes. Herein, we have successfully synthesized a zero-dimensional (0D) organic-inorganic hybrid mixed-metal halide (Bmpip)2PbxSn1-xBr4 (0 < x < 1, Bmpip+ = 1-butyl-1-methyl-piperidinium, C10H22N+) that crystallizes in a monoclinic system in the C2/c space group. Pb2+ and Sn2+ form a four-coordinate seesaw structure separated by organic cations forming a 0D structure. For different excitation wavelengths, (Bmpip)2PbxSn1-xBr4 (0 < x < 1) exhibits double-peaked emission at 470 and 670 nm. The emission color of (Bmpip)2PbxSn1-xBr4 can be easily tuned from orange-red to blue by adjusting the Pb/Sn molar ratio or excitation wavelength. Representatively, (Bmpip)2Pb0.16Sn0.84Br4 exhibits approximately white-light emission with high photoluminescence quantum yield up to 39%. Interestingly, the color of (Bmpip)2PbxSn1-xBr4 can also be easily tuned by temperature, promising its potential for application in temperature measurement and indication. Phosphor-converted light-emitting diodes are fabricated by combining (Bmpip)2PbxSn1-xBr4 and 365 nm near-UV LED chips and exhibit high-quality light output.

Highly efficient self-trapped exciton emission in a one-dimensional face-shared hybrid lead bromide

A new one-dimensional (1D) face-shared hybrid lead bromide of (2cepiH)PbBr3, which exhibits intrinsic broadband yellow-light emission with a quantum yield of 16.8% outperforming all previously reported 1D face-shared hybrid metal halides, is obtained. The origin of broadband emission and the coexistence of free excitons and self-trapped excitons are deeply investigated by variable-temperature photoluminescence spectra. Our work paves the way to discovering more wonderful light-emitting materials.

Combining Dual-Light Emissions to Achieve Efficient Broadband Yellowish-Green Luminescence in One-Dimensional Hybrid Lead Halides

In recent years, low-dimensional lead halides have emerged as some of most attractive photoelectric materials due to their intrinsic broadband emissions with a potential application in white-light emitting diodes. To achieve the desired performance, tremendous research has emphasized the modulation of inorganic components as optical centers; however, less work has paid attention to the direct contribution of the organic components. Herein, we successfully assembled two new hybrid lead halides of [H₂BPP]Pb₂X₆ (X = Br, 1, and Cl, 2) containing one-dimensional double [Pb₂X₆]^2- chains using optically active 1,3-bis(4-pyridyl)-propane (BPP) as an organic cation. Under UV-light excitation, compounds 1 and 2 exhibit broadband yellowish-green emissions, which were verified by promising photoluminescence quantum efficiencies (PLQEs) of 8.10% and 4.84%, respectively. The broadband light emissions are derived from the combination of dual higher-energy blue and lower-energy yellow light spectra, which can be attributed to the individual contributions of the organic and inorganic components, respectively, according to the time-resolved and temperature-dependent emission spectra as well as theoretical calculations. This work proves the great contribution of organic components to the photophysical properties and provides a new design strategy to realize broadband light emission by rationally combining the dual-emitting properties of different assembly blocks.

Zero-Dimensional Hybrid Organic-Inorganic Indium Bromide with Blue Emission

Low-dimensional hybrid organic-inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic-inorganic halide, RInBr₄, featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R⁺) cations and nonemissive InBr₄^- tetrahedral anions. The crystal structure of RInBr₄ is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l'Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

Organic cations directed 1D [Pb3Br10]4− chains: syntheses, crystal structures, and photoluminescence properties

To diversify the luminescence properties of 1D perovskites, different organic amine cations were combined with 1D [Pb₃Br₁₀]⁴⁻ chains leading to a series of A₂Pb₃Br₁₀ homologues, displaying broadband near white-light emissions with highest CRI of 96.

One-Dimensional Face-Shared Perovskites with Broad-Band Bluish White-Light Emissions

In recent years, two-dimensional (2D) hybrid lead halide perovskites based on corner-shared [PbX₆] octahedrons have received extensive attention with important potentials in single-component white-light emitting diodes (WLEDs) due to the soft and distorted crystal lattices. However, limited research focused on the one-dimensional (1D) perovskites although they possess similar structural superiorities to achieve this performance. Herein, by using different types of organic amine cations as structural direction reagents, we report one new type of hybrid 1D perovskites of APbCl₃ (A = (DTHPE)_0.5, DMTHP, DBN) based on the same 1D face-shared octahedral [PbCl₃]^- chains. Upon UV light excitation, these 1D APbCl₃ perovskites exhibit intrinsic broad-band bluish white-light emissions covering entire visible light spectra with the highest photoluminescence quantum yield (PLQY) of 6.99%, which catches up with the values of previously reported 2D perovskites. Through the systematical studies of time-resolved, temperature-dependent PL emissions, theoretical calculations, and so on, these broad-band light emissions can be ascribed to the radiative transition within conjugated organic cations. The facile assembly process, intrinsic broad-band light emissions, and high PLQYs enable these 1D APbCl₃ perovskites as new types of promising candidates in fabricating single-component WLEDs.

Improving Broadband White-Light Emission Performances of 2D Perovskites by Subtly Regulating Organic Cations

Recently, 2D organic-inorganic hybrid lead halide perovskites have attracted intensive attention in solid-state luminescence fields such as single-component white-light emitters, and rational optimization of the photoluminescence (PL) performance through accurate structural-design strategies is still significant. Herein, by carefully choosing homologous aliphatic amines as templates, isotypical perovskites [DMEDA]PbCl₄ (1, DMEDA=N,N-dimethylethylenediamine) and [DMPDA]PbCl₄ (2, DMPDA=N,N-dimethyl-1,3-diaminopropane) having tunable and stable broadband bluish white emission properties were rationally designed. The subtle regulation of organic cations leads to a higher degree of distortion of the 2D [PbCl₄ ]^2- layers and enhanced photoluminescence quantum efficiencies (<1 % for 1 and 4.9 % for 2). The broadband light emissions could be ascribed to self-trapped excitons on the basis of structural characterization, time-resolved PL, temperature-dependent PL emission, and theoretical calculations. This work gives a new guidance to rationally optimize the PL properties of low-dimensional halide perovskites and affords a platform to probe the structure-property relationship.

Hydrogen Bonding and Broad-Band Emission in Hybrid Zinc Halide Phosphors

In solid-state lighting (SSL) applications, hybrid zinc halide phosphors are a promising family because they meet specific criteria such as high color rendering, low cost, and nontoxicity. However, contrary to hybrid lead halide phosphors, their quantum efficiencies are low and the origin of this luminescence remains unclear. To unravel this origin and provide new insights into enhancement of this emission, four hybrid zinc halides have been investigated. These four compounds exhibit similar crystal structures but different photoluminescence properties. We show that photoemission requires the formation of V_k centers, which can be promoted by specific hydrogen bonding. We anticipate that the selection of a specific environment for the zinc halide units could lead to a promising family of low-cost and environmentally friendly phosphors for SSL.

Broadband yellow light emitting performance based on zero-dimensional hybrid lead bromide trimers

Two new zero-dimensional organic–inorganic hybrid lead halides based on linear [Pb₃Br₁₂]⁶⁻ trimers display broadband yellow light emissions with high photoluminescence quantum yields, exhibiting potential in the fabrications of white-light emitting diodes.

Tetrameric cluster assembled one-dimensional hybrid lead halides with broadband light emission

A series of new types of 1D lead halide perovskites have been synthesized based on [Pb₄X₁₆] tetrameric clusters. The 1D crystal lattice exhibits broadband yellow light emission arising from the self-trapped excitons with potential application in WLEDs.