Boosting Blue Self-Trapped Exciton Emission in All-Inorganic Zero-Dimensional Metal Halide Cs2ZnCl4 via Zirconium (IV) Doping.

Low-dimensional metal halides with efficient luminescence properties have received widespread attention recently. However, nontoxic and stable low-dimensional metal halides with efficient blue emission are rarely reported. We used a solvothermal synthesis method to synthesize tetravalent zirconium ion-doped all-inorganic zero-dimensional Cs2ZnCl4 for the first time. Bright blue emission in the range of 370 nm-700 nm with a emission maximum at 456 nm was observed in Zr4+:Cs2ZnCl4 accompanied by a large Stokes shift, which was due to self-trapped excitons (STEs) caused by the lattice vibrations of the twisted structure. Simultaneously, the PLQY of Zr4+:Cs2ZnCl4 achieve an impressive 89.67%, positioning it as a compelling contender for future applications in blue-light technology.

Efficient tunable white emission and multiple reversible photoluminescence switching in organic Tin(IV) chlorides via regulating the host lattice environment of antimony ions for multifunctional applications.

The host lattice environments of Sb3+ has a great influence on its photophysical properties. Here, we synthesized three zero-dimensional organic metal halides of (TPA)2SbCl5 (1), Sb3+-doped (TPA)SnCl5(H2O)·2H2O (Sb3+-2), and Sb3+-doped (TPA)2SnCl6 (Sb3+-3). Compared with the intense orange emission of 1, Sb3+-3 has smaller lattice distortion, thus effectively suppressing the exciton transformation from singlet to triplet self-trapped exciton (STE) states, which makes Sb3+-3 has stronger singlet STE emission and further bring a white emission with a photoluminescence quantum efficiency (PLQE) of 93.4%. Conversely, the non-emission can be observed in Sb3+-2 even though it has a similar [SbCl5]2- structure to 1, which should be due to its indirect bandgap characteristics and the effective non-radiative relaxation caused by H2O in the lattice. Interestingly, the non-emission of Sb3+-2 can convert into the bright emission of Sb3+-3 under TPACl DMF solution treatment. Meanwhile, the white emission under 315 nm excitation of Sb3+-3 can change into orange emission upon 365 nm irradiation, and the luminescence can be further quenched by the treatment of HCl. Therefore, a triple-mode reversible luminescence switch of off-onI-onII-off can be achieved. Finally, we demonstrated the applications of Sb3+-doped compounds in single-component white light illumination, latent fingerprint detection, fluorescent anti-counterfeiting, and information encryption.

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.

Generalized Synthesis of Highly-Dispersed, Ultrafine Transition Metal Nanoparticles on Silica Spheres for Enhanced Optical Absorption.

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5 nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. This work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiOx NSs) by forming a uniform coating of metal oxyhydroxide [MOy(OH)z] through preferred surface acid-base reactions and ii) thermally reducing MOy(OH)z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiOx NSs. The capability of this synthesis strategy is verified by loading ufMNPs of various transition metals and bimetallic combinations onto the SiOx NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiOx NSs, which generate intense electric fields near the surface of the SiOx NSs. The SiOx NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiOx-NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.

Realizing efficient broadband near-infrared emission and multimode photoluminescence switching via coordination structure modulation in Sb3+-doped 0D organic metal chlorides.

Recently, organic Sb(III)-based metal halides have achieved significant results in the visible light region due to their efficient emission. However, realizing efficient broadband near-infrared (NIR) emission in such materials is a great challenge. Herein, we developed three different NIR emitters via a coordination structure modulation strategy in Sb3+-doped zero-dimensional organic metal chlorides of (C20H20P)2MnCl4, (C20H20P)2ZnCl4, and (C20H20P)2CdCl4 with tetrahedral structure. More specifically, after the dopant Sb3+ is inserted into the host lattice, the coordination structures of Sb3+ ions can change from [SbCl5]2- square-pyramidal configuration to [SbCl4]- clusters, which will bring a larger lattice distortion degree to the excited state compared to the ground state, resulting in a larger Stokes shift. Thus, efficient NIR emission with near-unity photoluminescence quantum yield (PLQY) can be obtained in Sb3+-doped compounds under 365 nm excitation. Moreover, Sb3+-doped NIR emitters also show remarkable stabilities, which prompts us to fabricate NIR phosphor conversion light-emitting diodes (pc-LEDs) and demonstrate their application in night vision. More interestingly, the Sb3+-doped (C20H20P)2MnCl4 shows tunable emission characteristics, which can be tuned from green to greenish-yellow, orange, red, and NIR emission under different external stimuli, and thus we can demonstrate the applications of this compound in quintuple-mode fluorescence anti-counterfeiting and information encryption.

Sb3+-Doped Indium-Based Metal Halide (Gua)3InCl6 with Efficient Yellow Emission.

In recent years, low-dimensional organic-inorganic hybrid metal halides (OIHMHs) have shown excellent photophysical properties due to their quantum structure, adjustable energy levels, and energy transfer between inorganic and organic components, which have attracted extensive attention from researchers. Herein, we synthesize a zero-dimensional (0D) OIHMH, Sb3+:(Gua)3InCl6, by introducing Sb3+ into (Gua)3InCl6, which undergoes a significant enhancement of the emission peak at 580 nm with the photoluminescence quantum yield (PLQY) boosted from 17.86 to 95.72% when excited at 340 nm. This boost in photoluminescence of the doped sample was studied by combining ultrafast femtosecond transient absorption, temperature-dependent photoluminescence (PL) spectra, and density functional theory (DFT) calculation, revealing the process of self-trapped exciton (STE) recombination to emit light at both Sb and In sites in this 0D structure simultaneously. This material with the lowest dark STE level at the In site for emission in the undoped sample can amazingly yield very strong emission in the doped sample, which has never been observed before. Finally, we tested its application in a photoelectric device. This work not only helps to gain a deeper understanding of the formation of STEs in In-based halides but also plays a certain guiding role in the design of new luminescent materials.

Nickel(II)-Doped Lead-Free Halide Crystals Exhibiting Highly Efficient Tunable Blue-Emitting out of Antiferromagnetic Ni-Ni Coupling.

Metal halide crystals are widely used in optoelectronic fields due to their excellent optical properties. The hunt for a lead-free halide semiconductor with superior optical performance is a particularly fascinating topic in order to avoid the toxicity of lead. Here, we incorporate Ni2+ into a series of halide nanocrystals (NCs) through solution-phase synthesis. By modifying the A-site and varying the halide compositions, we successfully achieved significant tunability of the blue emission of the Ni2+-doped AX (A = K+, Rb+, NH2CH = NH2+ (FA), CH3NH3+ (MA); X = Br, I) NCs, ranging from 375 to 490 nm, due to the antiferromagnetic polaron (AMP), which is in contrast with the excitonic magnetic polarons (EMP) from those with ferromagnetic (FM) coupling between transition metal ions in similar compounds. This work shows that Ni2+-doped halide crystals could become a typical example providing AMP excitation as the optional emission centers for use in light emitting devices.

Excitation-Wavelength-Dependent Emission Behavior in (NH4)2SnCl6 via Sb3+ Dopant.

With high photoluminescence efficiency and a simple solution synthesis method, lead halide perovskites are expected to be a promising material for display and illumination. However, the toxicity and environmental sensitivity of lead hinder its potential applications. Here, we introduced Sb3+ ions into the lead-free perovskites derivative (NH4)2SnCl6 via a doping strategy. For the first time we synthesis the excitation-dependent perovskite with dynamically tunable fluorescence from yellow to near-infrared (NIR) emission by varying the UV excitation from 360 to 390 nm at room temperature. The DFT calculations are highly consistent no matter whether the coordination number of Sb3+ is 5 or 6. In contrasting to the early report of Sb triplet emission in the Sb doped perovskite, this material give a mixed self-trapped exciton (STE) emission. The 590 nm emission band is derived from the STE of SbCl5, and the 734 nm NIR emission band is attributed to the Sb-Sn mixed STE, which is supported by DFT calculations and spectral results. This study provides guidance for the design of perovskite phosphors with high efficiency and excitation-dependent properties.

Luminescence and Mechanism of Mn2+ Substitution in Cs7Cd3Br13 with Two Types of Coordination Number.

Cadmium-based perovskite materials as promising optoelectronic materials have been widely explored, but there are still some special microscopic interaction-dependent properties not fully understood. Here, we successfully synthesized Cs7(Cd1-XMnX)3Br13 crystal by a simple hydrothermal method. In Cs7Cd3Br13 crystals with their intrinsic self-trapped exciton (STE) emission, Cd2+ ions stay in both different coordination sites, and partial replacement of Cd2+ with Mn2+ can modify their luminescence properties significantly. The luminescence peak position of the doped sample was adjusted from 610 nm in the undoped sample to 577 nm in the doped one by the combination of STE and Mn d-d transition, with enhanced photoluminescence quantum yield (PLQY) of ∼50% at a Mn precursor ratio of 40%. Their magnetic responses occur from the coexisting ferromagnetic (FM) and antiferromagnetic (AFM) coupling of Mn pairs in four and six coordination sites, modifying its whole emission profile. This material is valuable for studying the structure-optical properties and finding applications in optoelectronic devices.

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.

Realizing High-Efficiency Yellow Emission of Organic Antimony Halides via Rational Structural Design.

Zero-dimensional (0D) organic metal halides have captured extensive attention for their various structures and distinguished optical characteristics. However, achieving efficient emission through rational crystal structure design remains a great challenge, and how the crystal structure affects the photophysical properties of 0D metal halides is currently unclear. Herein, a rational crystal structure regulation strategy in 0D Sb(III)-based metal halides is proposed to realize near-unity photoluminescence quantum yield (PLQY). Specifically, two 0D organic Sb(III)-based compounds with different coordination configurations, namely, (C25H22P)2SbCl5 and (C25H22P)SbCl4 (C25H22P+ = benzyltriphenylphosphonium), were successfully obtained by precisely controlling the ratio of the initial raw materials. (C25H22P)2SbCl5 adopts an octahedral coordination geometry and shows highly efficient broadband yellow emission with a PLQY of 98.6%, while (C25H22P)SbCl4 exhibits a seesaw-shaped [SbCl4]- cluster and does not emit light under photoexcitation. Theoretical calculations reveal that, by rationally controlling the coordination structure, the indirect bandgap of (C25H22P)SbCl4 can be converted to the direct bandgap of (C25H22P)2SbCl5, thus ultimately boosting the emission intensity. Together with efficient emission and outstanding stability of (C25H22P)2SbCl5, a high-performance white-light emitting diode (WLED) with a high luminous efficiency of 31.2 lm W-1 is demonstrated. Our findings provide a novel strategy to regulate the coordination structure of the crystals, so as to rationally optimize the luminescence properties of organic metal halides.

Competing Energy Transfer-Modulated Dual Emission in Mn2+-Doped Cs2NaTbCl6 Rare-Earth Double Perovskites.

A2BIBIIIX6 double perovskites are promising materials due to their outstanding photoelectronic properties and excellent stability in the environment. Herein, we synthesized Mn2+:Cs2NaTbCl6 with dual emission through a solvothermal method for the first time. Mn2+:Cs2NaTbCl6 double perovskites exhibit excellent environmental stability and high photoluminescence quantum yields (PLQYs). The Cs2NaTbCl6 was successfully doped with Mn2+ in two modes: at Mn-feeding concentrations below 1%, Mn2+ first tend to insert into the interstitial void, but if the Mn-feeding concentration exceeds 1%, Mn2+ will further substitute Na+ site of the Cs2NaTbCl6 lattice and thus both two doping modes coexist. After Mn2+ doping, efficient energy transfer from the 5D4 level of Tb3+ ions to the 4T1 level of Mn2+ ions occurs, resulting in tunable dual emission from the Tb3+5D4 → 7FJ=6,5,4,3 transition and Mn2+4T1 → 6A1 transition. Further, LED based on the Mn2+:Cs2NaTbCl6 double perovskites exhibits excellent performance and stability. This work demonstrates a strategy to achieve novel lanthanide-based double perovskites with potential applications in photonics.

Green Triplet Self-Trapped Exciton Emission in Layered Rb3Cd2Cl7:Sb3+ Perovskite: Comparison with RbCdCl3:Sb3.

Metal halide materials have recently sparked intense research because of their excellent photophysical properties and chemical stability. For example, RbCdCl3:Sb3+ exhibits broad emission at about 600 nm with a high photoluminescence quantum yield (PLQY) over 91% and double emission bands with bright white color. Herein, we obtained a novel Rb and Cd layered perovskite Rb3Cd2Cl7 doped with Sb3+, which gives luminescence at 525 nm with a large Stokes shift of 200 nm, originating from a self-trapped exciton (STE). Its PLQY is 57.47%, but its low-temperature PLQY becomes much higher at the same wavelength. When Rb3Cd2Cl7:Sb3+ and RbCdCl3:Sb3+ were compared, the two classes of quantum confinement effects by Rb and Cd ions in the lattice were identified to describe their electronic states and different optical properties. These results suggest that properties of Sb-doped cadmium halides could be modified by the structure type and local atomic confinement to find applications as promising luminescent materials for optoelectronic devices.

A Zero-Dimensional Organic Lead Bromide of (TPA)2PbBr4 Single Crystal with Bright Blue Emission.

Blue-luminescence materials are needed in urgency. Recently, zero-dimensional (0D) organic metal halides have attractive much attention due to unique structure and excellent optical properties. However, realizing blue emission with near-UV-visible light excitation in 0D organic metal halides is still a great challenge due to their generally large Stokes shifts. Here, we reported a new (0D) organic metal halides (TPA)2PbBr4 single crystal (TPA+ = tetrapropylammonium cation), in which the isolated [PbBr4]2- tetrahedral clusters are surrounded by organic ligand of TPA+, forming a 0D framework. Upon photoexcitation, (TPA)2PbBr4 exhibits a blue emission peaking at 437 nm with a full width at half-maximum (FWHM) of 50 nm and a relatively small Stokes shift of 53 nm. Combined with density functional theory (DFT) calculations and spectral analysis, it is found that the observed blue emission in (TPA)2PbBr4 comes from the combination of free excitons (FEs) and self-trapped exciton (STE), and a small Stokes shift of this compound are caused by the small structure distortion of [PbBr4]2- cluster in the excited state confined by TPA molecules, in which the multi-phonon effect take action. Our results not only clarify the important role of excited state structure distortion in regulating the STEs formation and emission, but also focus on 0D metal halides with bright blue emission under the near-UV-visible light excitation.

H2O-NH4+-Induced Emission Modulation in Sb3+-Doped (NH4)2InCl5·H2O.

Lead-based metal halide perovskites have received widespread attention for their promising application prospects in the field of lighting and display due to their excellent optical properties. However, the toxicity of lead may hinder their further commercial application. Herein, a zero-dimensional (0D) metal halide (NH4)2InCl5·H2O with an orthorhombic structure and the Pnma space group was produced. With doping with Sb3+, these products exhibit one highly efficient and wide yellow emission band (∼450-850 nm) in their photoluminescence (PL) spectra, which covers almost the entire visible spectral range at room temperature; however, they give two emission bands with long decay lifetimes (microseconds) at low temperature. Temperature-dependent steady-state PL, transient PL spectroscopy, temperature-dependent Raman spectra characterization, and theoretical band structure calculations confirm that the dual-band emission at low temperature originates from the dual vibronic levels of the self-trapped exciton (STE) in the hole-vibration state, whose vibration energy is related to the H2O-NH4+ connection in the valence band. This result proves that the vibronic state in STE formation involves both electrons and holes in the excited states, the opposite of this happens in the electron-vibration band in most perovskite halides. These results provide new insight into the luminescent mechanism of Sb3+ in halide perovskites, especially used for emission color modulation by the temperature-dependent electron- or hole-vibration processes.

Efficient Orange Emission in Mn2+-Doped Cs3Cd2Cl7 Perovskites with Excellent Stability.

Low-dimensional metal halides are attractive for applications in photodetectors, solid-state lighting, and solar cells, but poor stability is an obstacle that must be overcome in commercial applications. Herein, we successfully synthesized a Ruddlesden-Popper (RP)-phased perovskite Mn2+:Cs3Cd2Cl7 with high photoluminescence quantum yield (PLQY) and outstanding thermal and environmental stability by a solvothermal method. The pristine sample Cs3Cd2Cl7 exhibits a weak cyan broad emission centered at 510 nm with a low PLQY of ∼4%. Once Mn2+ ions are introduced into the host lattice, a bright orange emission peaking at 580 nm with a high PLQY of ∼74% was achieved, which is attributed to the efficient energy transfer from the host to Mn2+ ions and thus results in the 4T1 → 6A1 radiation transition of Mn2+ ions. The photoluminescence (PL) intensity and environmental stability of Mn2+:Cs3Cd2Cl7 can be further improved through A-site Rb alloying. Finally, an orange LED with outstanding color stability was fabricated on the basis of the Mn2+:Cs3Cd2Cl7. Our work successfully elucidates that dopant plays an integral role in tailoring optical properties.

Phase-Selective Solution Synthesis of Cd-Based Perovskite Derivatives and Their Structure/Emission Modulation.

The rich phase structures of perovskite derivatives have attracted extensive attention and can be applied in the fields of optoelectronics due to their high emission efficiency and tunable emission. Herein, we explored a phase-selective solution synthetic route to obtain different Cd-based perovskite derivatives. First, the pristine tetragonal Cs7Cd3Br13 was obtained by a solvothermal method, and its photoluminescence quantum yield (PLQY) was boosted from 8.28% to 57.62% after appropriate Sb3+ doping. Furthermore, halogen substitution was adopted to modify Sb:Cs7Cd3Br13 and produced a series of Cd-based perovskite derivatives with different crystal structures and tunable emission from cyan to orange (517-625 nm). The mechanisms behind such experimental phenomena were further investigated and discussed on the basis of material characterization and theoretical computation. This study presented an effective strategy to synthesize bright Cd-based perovskite derivatives with different structures and modulated emission, and it also provided insights to understand the structure/emission modulation via halogen substitution.

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 3Pn (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.

Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer.

Organic-inorganic hybrid metal halides have been widely studied as a kind of phosphor materials for high-performance white light-emitting diodes. In this paper, a series of organic-inorganic metal-halide (C3H10N)4Pb1-xMnxBr6 powders with different Mn2+ ion doping concentrations were synthesized by mechanochemical methods, giving broadband white light emission with a photoluminescence quantum yield of 36.1% at room temperature, which turn green with a much larger intensity at 80 K. Interestingly, its emission converted from white to red after 100 °C treatments and turned back to white again when exposed to moist air for a while. This emission variation was caused by the adsorbed water layer on the surface of product powders via the dielectric confinement. The red emission from no water powders is identified to occur from the Mn ferromagnetic pair in point-shared octahedral sites, while the broadband white emission originated from the surface water-assisted dielectric confinement and surface polarization which combine the self-trapped excitons and d-d transitions of Mn ions and Mn pairs in the product. Moreover, this white emission can transform into green color at 80 K with a much stronger intensity, caused by the even efficient surface dielectric confinement by the adsorbed frozen water layer. This special compound has the advantages of simple preparation, low cost, and good stability and even contains water molecule in the air, giving a near-perfect white emission, with CIE of (0.33, 0.35) and correlated color temperatures at around 5733 K, which may be used for different applications such as sensing, solid-state lighting, and display.