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

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.

Natural Pigments-Based Two-Component White Light Emitting Systems

In this paper, a new class of two component white light emitting systems viz, JaB (java plum + beetroot) {I}, and CaB (carrot + beetroot) {II} were developed through resonance energy transfer (RET) phenomenon by using a fruit (java plum) and two vegetable (carrot and beetroot) extracts. In these white light emitting systems, java plum and carrot are the donors while beetroot is the acceptor. The primary fluorescent pigments present in the natural extracts (i.e., anthocyanin in java plum, β-carotene in carrot, and betanin in beetroot) were responsible for the white light emission. The CIE (Commission Internationale d'Eclairage) coordinates for I and II were {0.32, 0.34} and {0.33, 0.33}, respectively, in solution phase. Interestingly, the white light emission (WLE) was also achieved in agar-agar gel medium. In gel medium, the CIE values were {0.31, 0.34} and {0.33, 0.32} for I and II, respectively. The donor-acceptor distance (r) for I and II were found to be 0.5 and 0.4 nm, respectively. Furthermore, the rate of energy transfer was also quantified with the values of 2.78 × 109 s-1 for JaB (I) and 1.02 × 108 s-1 for CaB (II) systems. The mechanistic investigation of the two white light systems was further supported by DFT studies.

Full-Spectrum White-Light Emission from Triple Self-Trapped Excitons in Hybrid Mixed-Metal Halides

Low-dimensional metal halides with broadband emissions are expected to serve as downconversion luminescent materials for solid-state lighting (SSL). However, efficiently generating full-spectrum white-light emission with a high color-rendering index (CRI) in single-phase emitters remains a challenge. Here, we report a novel zero-dimensional (0D) hybrid mixed-metal halide (TPA)2CuAgI4 (TPA = tetrapropylammonium), in which individual [CuAgI4]2- dimers are completely isolated and surrounded by the organic cations TPA+. Cu+ and Ag+ share the same crystallographic site in [CuAgI4]2- dimers with the same statistical probability. Upon photoexcitation, single crystals exhibit a full-spectrum white-light emission with a full width at half-maximum (fwhm) of up to 314 nm and a high quantum efficiency of 46.8%. Detailed photophysical studies and theoretical calculations reveal that the ultra-broadband emission of (TPA)2CuAgI4 originates from the radiative recombination of red-, green-, and blue-emitting self-trapped excitons in [CuAgI4]2- dimers. In addition, (TPA)2CuAgI4 nanocrystals were successfully synthesized and exhibited optical properties similar to those of single-crystal counterparts. Finally, a prototype ultraviolet (UV)-pumped white-light-emitting diode (WLED) and a composite thin film employing this new white-light emitter produces a well-distributed full-spectrum white light with a high CRI of 91.4 and a warm correlated color temperature (CCT) of 4135 K, indicating the potential application of this white-light emitter in SSL. These results provide a new perspective for designing superior single-phase white-light emitters.

Zero-Dimensional Halides with ns2 Electron (Sb3+) Activation to Generate Broad Photoluminescence

Organic-inorganic metal halides (OIMHs) have various crystal structures and offer excellent semiconducting properties. Here, we report three novel OIMHs, (PPA)₆InBr₉ (PPA = [C₆H₅(CH₂)₃NH₃]⁺), (PBA)₂SbBr₅, and (PBA)₂SbI₆ (PBA = [C₆H₅(CH₂)₄NH₃]⁺), showing typical zero-dimensional (0D) structure, octahedra dimers, and corner-sharing one-dimensional chains and crystallized in the monoclinic system with P2₁, P2₁/c, and C2/c space groups, respectively. (PPA)₆InBr₉, (PBA)₂SbBr₅, and (PBA)₂SbI₆ have experimental optical band gaps of ∼3.16, ∼2.24, and 1.48 eV, respectively. (PPA)₆InBr₉ exhibits bright-orange light emission centered at 642 nm with a full-width at half-maximum of 179 nm (0.51 eV) and a Stokes shift of 277 nm (1.46 eV). After Sb³⁺ doping, the peak position did not change, and the photoluminescence quantum yield increased significantly from 9.2 to 53.0%. The efficient emission of Sb:(PPA)₆InBr₉ stems from the isolated ns² luminescent center and strong electron-phonon coupling, making the spin-forbidden ³P₁-¹S₀ observable. By combining commercial blue and green phosphors with orange-red-light-emitting (PPA)₆In_0.99Sb_0.01Br₉, a white-light-emitting diode was constructed, with the color-rendering index reaching up to 92.3. Our work highlights three novel 0D OIMHs, with chemical doping of Sb³⁺ shown to significantly enhance the luminescence properties, demonstrating their potential applications in solid-state lighting.

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

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

Synthetic-Method-Dependent Antimony Bromides and Their Photoluminescent Properties

Recently, excellent optical properties of low-dimensional organic-inorganic metal halides, stemming from their tunable structure and optoelectronic properties, have been demonstrated. The synthetic method is critical because it is highly related to the structure and properties of the halide. Herein, we obtain two different antimony bromides, (Bmpip)₂SbBr₅ and (Bmpip)₃Sb₂Br₉, which both possess the P2₁/c space group having different crystal structures, and this confirms the important influence of synthesis on the single-crystal structure. (Bmpip)₂SbBr₅ contains Bmpip⁺ and [SbBr₅]^2- pyramids, and (Bmpip)₃Sb₂Br₉ consists of Bmpip⁺ and Sb-based dimers [Sb₂Br₉]^3-. Under 400 nm excitation, (Bmpip)₂SbBr₅ exhibits a 640 nm orange emission with a quantum yield of ∼11.5% owing to Sb 5s² electron luminescence. A diode was fabricated by (Bmpip)₂SbBr₅ and commercial phosphors and showed a high color render index of 92. Our work reveals the effect of the preparation method on the crystal structure. A luminescent material was finally identified.

Competitive Dual-Emission-Induced Thermochromic Luminescence in Organic-Metal Halides

Lead-free Halides, especially Mn-based ones, are preferred as hotspots in the exploration of photoluminescent materials. However, there are few reports on sensitive reversible thermochromism and switchable dual emission originating from self-trapped exciton emission in pure Mn-Based materials. Here, we report a new Mn-based hybrid material [TMPA]₂MnI₄ (TMPA = trimethylphenylammonium), which shows two emission peaks at 545 and 660 nm benefitting from the d-d orbital transition of Mn²⁺ and the generation of self-trapped excitons, respectively. Due to the different sensitivity to temperature, the stages of thermal activation and thermal quenching of the two emission types are also inconsistent, showing a certain competition relationship and dominating the emission colors in different temperature ranges, resulting in adjustable green-orange-green thermochromic luminescence from 100 to 403 K (both high and low temperatures correspond to green, and orange is displayed at near room temperature). Therefore, thermochromic luminescence can be easily achieved by controlling the temperature under the guidance of excited states. This work provides new insights into the synthesis and application of thermochromic materials. Therefore, it is certain that regulating temperature while being guided by excited states will achieve thermochromic luminescence. This research offers fresh perspectives on the development and potential of thermochromic materials.

Color tunable of Ln-MOFs (Ln = Tb, Eu) and excellent stability for white light-emitting diode

White light-emitting diodes (WLEDs) possess the advantages of environmental friendliness, long lifetime, and energy saving. Recently, metal-organic frameworks (MOFs) have become one of the hot candidates for LEDs. However, the tunable color and thermal stability of MOFs are urgent problems for their actual applications. In this work, Ln-MOFs (Ln = Eu, Tb) were synthesized by a facile wet chemical route. A series of Ln-MOFs phosphors with tunable luminescence color showed potential applications in white LEDs. The emission color of the phosphors can be easily modulated by changing the molar ratio of the raw materials. The luminescence intensities of Ln-MOFs retained over 90.6% of the initial value, showing excellent thermal stability of Ln-MOFs. In order to explore the potential applications of Ln-MOFs in WLEDs, we mixed them with two kinds of blue phosphors and packaged them to obtain WLEDs. The CIE coordinates of both were (0.31, 0.33) and (0.31, 0.34), which were able to achieve white light emission. The peak shape and peak position in the EL spectrum of the WLEDs device remained stable when increasing the applied current of the device. Meanwhile, the white light with excellent color quality and visual performance was achieved. The results show that Ln-MOFs are potential materials for white light LED, and provide a novel idea for the application of Ln-MOFs materials in the luminescence field.

Pure White Emission with 91.9% Photoluminescence Quantum Yield of [(C3H7)4N]2Cu2I4 out of Polaronic States and Ultra-High Color Rendering Index

Recently, cuprous halide perovskite-type materials have drawn tremendous attention for their intriguing optical properties. Here, a zero-dimensional (0D) Cu(I)-based compound of [(C₃H₇)₄N]₂Cu₂I₄ ([C₃H₇)₄N]⁺ = tetrapropylammonium cation) was synthesized by a facile solution method, a monoclinic system of P2₁/n symmetry with a Cu₂I₄^2- cluster as the confined structure. The as-synthesized [(C₃H₇)₄N]₂Cu₂I₄ exhibits bright dual-band pure white emission with a photoluminescence quantum yield (PLQY) of 91.9% and CIE color coordinates of (0.33, 0.35). Notably, this compound also exhibits an ultrahigh color rendering index (CRI) of 92.2, which is comparable to the highest value of single-component metal halides reported recently. Its Raman spectra provide a clear spectral profile of strong electron-phonon interaction after [(C₃H₇)₄N]⁺ incorporation, favoring the self-trapped exciton (STE) formation. [(C₃H₇)₄N]₂Cu₂I₄ can give dual-STE bands at the same time because of the Cu-Cu metal bond in a Cu₂I₄^2- cluster, whose populations could be scaled by temperature, together with the local dipole orientation modulation of neighboring STEs and phase transition related emission color coordinate change. Particularly, the outstanding chemical- and antiwater stability of this compound was also demonstrated. This work illustrates the potential of such cuprous halide perovskite-type materials in multifunctional applications, such as lighting in varied environments.

Light/Force-Sensitive 0D Lead-Free Perovskites: From Highly Efficient Blue Afterglow to White Phosphorescence with Near-Unity Quantum Efficiency

Herein, new types of zero-dimensional (0D) perovskites (PA6InCl9 and PA4InCl7) with blue room-temperature phosphorescence (RTP) were obtained from InCl₃ and aniline hydrochloride. These are highly sensitive to external light and force stimuli. The RTP quantum yield of PA6InCl9 can be enhanced from 25.2 % to 42.8 % upon illumination. Under mechanical force, PA4InCl7 exhibits a phase transform to PA6InCl9, thus boosting ultralong RTP with a lifetime up to 1.2 s. Furthermore, white and orange pure RTP with a quantum yield close to 100 % can be realized when Sb³⁺ was introduced into PA6InCl9. The white pure phosphorescence with a color-rendering index (CRI) close to 90 consists of blue RTP of PA6InCl9 and orange RTP of Sb³⁺ . Thus, this work not only overcomes long-standing problems of low quantum yield and short lifetime of blue RTP, but also obtains high-efficiency white RTP. It provides a feasible method to realize near-unity quantum efficiency and has great application potential in the fields of optical devices and smart materials.

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)₄Pb_1-xMn_xBr₆ 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.

Zero-Dimensional Lead-Free Halide with Indirect Optical Gap and Enhanced Photoluminescence by Sb Doping

Three new lead-free organic-inorganic metal halides (OIMHs) (C₇H₈N₃)₃InX₆·H₂O (X = Cl, Br) and (C₇H₈N₃)₂SbBr₅ were synthesized. First-principles calculations indicate that the highest occupied molecular orbitals (HOMOs) of the two In-based OIMHs are constituted of π orbitals from [C₇H₈N₃]⁺ spacers. (C₇H₈N₃)₃InX₆·H₂O (X = Cl, Br) shows an indirect optical gap, which may result from this organic-contributed band edge. Despite the indirect-gap nature with extra phonon process during absorption, the photoluminescence of (C₇H₈N₃)₃InBr₆·H₂O can still be significantly enhanced through Sb doping, with the internal photoluminescence quantum yields (PLQY) increased 10-fold from 5% to 52%. A white light-emitting diode (WLED) was fabricated based on (C₇H₈N₃)₃InBr₆·H₂O:Sb³⁺, exhibiting a high color-rendering index of 90. Our work provides new systems to deeply understand the principles for organic spacer choice to obtain the 0D metal OIMHs with specific band structure and also the significant enhancement of luminescence performance by chemical doping.