Efficient White Light Emission Research Articles

Pillar[5]arene-based light-harvesting assemblies with sequential energy-transfer for tunable emission and photocatalysis

Sequential energy transfer widely exists in natural light-harvesting systems (LHSs), which greatly benefits the full use of solar energy. In this work, we report an artificial light-harvesting platform derived from pillar (Wang et al., 2021) [5]arene-directed host-guest nanoparticles (WP5⊃G) in aqueous media. The WP5⊃G assembly can serve as a good donor owing to the excellent fluorescence behavior of G in the aggregated state, guaranteeing a two-step FRET from the WP5⊃G to the relay acceptor eosin Y (ESY) and then to the final acceptor Nile red (NiR) to form a WP5⊃G@ESY/NiR system with high efficiency. As a consequence of the flexibility of the system, tunable emission including a highly efficient white-light emission can be realized. The WP5⊃G@ESY/NiR system was further used as a photocatalyst to catalyze dehalogenation reaction in aqueous solution, exhibiting remarkable catalytic activity as compared with the WP5⊃G or ESY/NiR alone.

High-order Raman scattering mediated by self-trapped exciton in halide double perovskite

High-order Raman scattering is a typical photophysical process in understanding the electron--phonon coupling (EPC) in materials. In a ``soft'' polar lattice, due to the strong EPC, the excited electron-hole pairs can be captured by the lattice deformation potential, forming the self-trapped exciton (STE). Although high-order Raman scattering mediated by STE has been predicted by theory, there are rare experimental reports, especially in the double perovskite ${\mathrm{Cs}}_{2}{\mathrm{Ag}}_{0.4}{\mathrm{Na}}_{0.6}{\mathrm{InCl}}_{6}$, with highly efficient white light emission. We observed high-order Raman mode up to 12 orders at 4 K in ${\mathrm{Cs}}_{2}{\mathrm{Ag}}_{0.4}{\mathrm{Na}}_{0.6}{\mathrm{InCl}}_{6}$ by resonance excitation. We propose a physical picture of high-order Raman scattering mediated by STE to explain well the linear dependence of frequency and linewidth with order number. A reduction in the EPC with a temperature increase is attributed to the breakdown of momentum conservation during high-order scattering and the delocalization of the STE. Our work deepens the understanding of the EPC in STE and inspires the research of the excited-state decay process.

Coupling Intracompound Charge Transfer and Cluster‐Centered Excited States in Cu(I) Halide Hybrids for Efficient White Light Emission

Abstract0D hybrid organic–inorganic metal halides have attracted significant interest due to their unique optoelectronic properties, but attainment of efficient and stable white light emission (WLE) in such compounds remains a challenge. Here, efficient WLE via a molecular design that couples intracompound charge transfer and cluster‐centered excited states in 0D halide hybrids is demonstrated. Two Cu(I) halide hybrids, K(18‐crown‐6)Cu2Br3 and Na4(18‐crown‐6)5In2Cu4Br14·8H2O, are synthesized wherein luminescent [Cu4Br6]2− clusters are isolated from each other and surrounded by 18‐crown‐6 coordinated alkali metal cations. In the case of K(18‐crown‐6)Cu2Br3, [Cu4Br6]2− clusters are only partially isolated, leading to strong orange emission with a photoluminescence quantum yield (PLQY) of 53% under UV excitation. Strikingly, to a larger extent of isolation as that, in Na4(18‐crown‐6)5In2Cu4Br14·8H2O as a result of the incorporation of nonemissive [InBr4]− clusters, intense white light emission with a PLQY of 97% is achieved. The dual cluster‐centered states, coupled with a mixed metal‐to‐ligand and halide‐to‐ligand charge transfer state, are responsible for this bright white luminescence. This work provides new design principles for expanding the materials library for single‐component, solid‐state WLE.

Rapid and Large-Scale Preparation of Stable and Efficient White Light Emissive Perovskite Microcrystals Using Ionic Liquids.

In this work, we report large-scale preparation of stable Sb3+ and Bi3+ codoped Cs2ZrCl6 microcrystals for highly efficient white light emission using ionic liquids, demonstrating a broad dual-band white emission covering 400-800 nm. The dual emissions originate from the associated self-trapped excitons of the [SbCl6]3- and [BiCl6]3- octahedra. Moreover, the ratio of the dual-emission peaks can be effectively regulated by tuning the excitation wavelength. Meanwhile, to improve the optical properties and stability, ionic liquids are employed to assist the synthesis process of perovskite materials. The white light emission of one of the samples demonstrates CIE coordinates right in the center of the white light region (0.334, 0.331) and an excellent color rendering index (∼90.3), accompanied by a 66.1% quantum efficiency. Moreover, our method allows the facile synthesis of large batches of microcrystalline powders. Our findings demonstrate the potential of white phosphors as single components for future applications in lighting fields.

Janus-Structural AIE Nanofiber with White Light Emission and Stimuli-Response.

White-light emitting elastomers (WLEEs) based on stimuli-responsive aggregation-induced emission (AIE) and regulated Förster resonance energy transfer (FRET) have aroused increasing attention due to the demands for wearable optoelectronic devices. Herein, the blue and orange AIEgens with different environmental sensitivities are synthesized and then encapsulated on both sides of nanofibers via side-by-side electrospinning aiming to achieve the Janus WLEEs. After regulating the blue-orange AIEgens ratio, efficient and stable white light emission with a CIE coordinate of about (0.33, 0.31) is achieved at a blue-orange AIEgens mass ratio of 3:1. Besides, the Janus nanofibers (Janus-NFs) also present super stretchability with elongation at the break over 150% and tensile strength close to 7MPa. The sensitivity of fluorescence for Janus-NFs to its stretching deformation is used to visualize the evolution of the microstructure of nanofibers during stretching. Moreover, the Janus-NFs are also sensitive to HCl and NH3 , of which the fluorescence color would change under HCl and NH3 fuming above 2 and 57ppm in air, respectively. The promising applications of the white light Janus-NFs in smart fabrics, warning sensors, and anti-counterfeiting packaging are demonstrated. This finding provides an efficient strategy for achieving wearable WLEEs with multiple functionalities, promoting the development of wearable devices.

White-light emission from organic aggregates: a review

White light, which contains polychromic visible components, affects the rhythm of organisms and has the potential for advanced applications of lighting, display, and communication. Compared with traditional incandescent bulbs and inorganic diodes, pure organic materials are superior in terms of better compatibility, flexibility, structural diversity, and environmental friendliness. In the past few years, polychromic emission has been obtained based on organic aggregates, which provides a platform to achieve white-light emission. Several white-light emitters are sporadically reported, but the underlying mechanistic picture is still not fully established. Based on these considerations, we will focus on the single-component and multicomponent strategies to achieve efficient white-light emission from pure organic aggregates. Thereinto, single-component strategy is introduced from four parts: dual fluorescence, fluorescence and phosphorescence, dual phosphorescence with anti-Kasha’s behavior, and clusteroluminescence. Meanwhile, doping, supramolecular assembly, and cocrystallization are summarized as strategies for multicomponent systems. Beyond the construction strategies of white-light emitters, their advanced representative applications, such as organic light-emitting diodes, white luminescent dyes, circularly polarized luminescence, and encryption, are also prospected. It is expected that this review will draw a comprehensive picture of white-light emission from organic aggregates as well as their emerging applications.

Fabrication of a light-emitting device based on the CdS/ZnS spherical quantum dots

In this work, we focus on the colloidal quantum dot based light-emitting diodes (QD-LEDs) performance. First, we synthesize the spherical QDs with a CdS core that covered with a wider band gap II–VI semiconductor acting as a shell (ZnS). In order to synthesize this nano crystal QDs with structure of CdS/ZnS/CdS/ZnS, we use a reverse micelle process. These four-layer quantum well quantum dots (QWQDs) can generate the white light emission. The positional design of different layers i.e., core/shell QD emitters is a critical factor for white emissive devices. The blue emission generated by CdS core mixes with green/orange components originating from ZnS inner shell and creates an efficiency white light emission. Then, we fabricate a white-QDLED with a device structure of FTO/ ZnO / QD / CBP/ MoO3 / Al films. A thin film of CdS/ZnS/CdS/ZnS QDs is deposited by electrostatically assembled colloidal QD solutions. The experimental results show that the emission spectra of QDs and current density through the LED are controlled by varying the particle sizes. The peaks of absorbance and Photoluminescence (PL) spectrums for core/shell structures get the red shifted as the dot size increases. Furthermore, this QD-LED with a smaller nano particle layer has a higher current density.

Efficient white light emission from a single silicate host with promising color quality for white light emitting diodes

Strontium silicate phosphors were synthesized via a solid-state route with different silicon sources as SiO2 and Si3N4. The phosphors synthesized with Si3N4 exhibited improved luminescence properties for white emission because of the coexistence of Sr3MgSi2O8 and Sr2SiO4 phases. Under UV excitation, white light was observed due to the combination of blue emission from Sr3MgSi2O8: Eu2+ and yellow emission from Sr2SiO4: Eu2+. The broad Eu2+ emission was explained on the basis of the dependency of crystal field strength on the site selection. The variation of Eu2+ ion concentration controlled the quality of the emitted light and at 5 mol% Eu2+, near white emission (0.30, 0.31) was obtained with external and internal quantum efficiencies of 50% and 68%, respectively. The WLEDs were fabricated by coating the present phosphors on an InGaN UV- LED chips and the EL spectrum displayed near white chromaticity (0.31, 0.33) with color rendering index of 80 and CCT of 6850 K. The results demonstrated the promising single host phosphors for near-UV white-light-emitting diodes.

Highly Efficient and Solution‐Processed Single‐Emissive‐Layer Hybrid White Organic Light‐Emitting Diodes with Tris(triazolo)triazine‐Based Blue Thermally Activated Delayed Fluorescence Emitter

AbstractSolution processable organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters show inferior efficiency to devices produced via vacuum deposition. In this context, solution‐processed hybrid white OLEDs are fabricated using a TADF molecule and iridium complex as the blue and red dopants, respectively. First, solution‐processed OLEDs employing a tristriazolotriazine‐based TADF as the blue dopant are designed and fabricated, yielding maximum external quantum efficiency (EQEmax) of 23.23% with an emission peak at 492 nm. Use of the optimized tristriazolotriazine‐based TADF OLED structure and additional red phosphor achieves highly efficient white light emission with an EQEmax of 22.57%, stable Commission International de l'Eclairage (CIE) coordinates of (0.34, 0.34), a correlated color temperature of 5000 K, and a color rendering index of 73. Impressively, accelerated lifetime testing shows the white OLED possessing a lifetime to 80% of initial luminance (LT80) of 40 h, and an LT50 of 298 h. To the best of knowledge, the device performance demonstrated in this work is one of the best comprised of solution‐processed blue and fluorescent‐phosphorescent hybrid white OLEDs. This research provides a reliable method for high efficiency solution processable blue TADF and TADF‐phosphorescent hybrid OLEDs.

Highly Efficient White-Light Emission Induced by Carboxylic Acid Dimers in a Layered Hybrid Perovskite

Broadband white-light emission in metal halides has been intensely explored because of their facile solution processability, structural adjustability, and high color rendering index. However, the m...

Efficient White Light Emission from Ga/Ga2O3 Hybrid Nanoparticles

AbstractGallium (Ga) emerges as a promising material in plasmonics mainly due to its extraordinary properties, such as changeable material phase, tunable plasmon resonances across the ultraviolet to near‐infrared spectral range, and remarkable chemical stability. Here, the efficient white light emission from gallium oxide (Ga2O3) nanoparticles doped with liquid Ga nanodots, which are fabricated by using a laser‐induced oxidation method is reported. The quantum efficiency of Ga/Ga2O3 hybrid nanoparticles is found to be ≈1.3%, which is nearly two orders of magnitude larger than that of liquid Ga nanoparticles. It is revealed that the existence of Schottky barrier and hotspots in Ga/Ga2O3 nanoparticles plays a crucial role in enhancing the quantum efficiency. As an example of practical applications, high‐quality optical data storage is demonstrated by exploiting the controllable formation of Ga/Ga2O3 nanoparticles on a platform of disordered Ga nanoislands. These results suggest the potential applications of Ga/Ga2O3 hybrid nanoparticles in the development of nanoscale light sources and data storage devices.

Ultrafast Dynamics of Self-Trapped Excitons in Lead-Free Perovskite Nanocrystals.

Lead-free halide perovskite nanocrystals (NCs) have received increasing attention owing to their low toxicity and high stability. Localized charge distribution and strong carrier-phonon coupling in lead-free perovskite NCs facilitates the formation of self-trapped excitons (STEs), which typically give a broadband photoluminescence (PL) emission with a large Stokes shift. In this Perspective, we highlight how PL modulations can give rise to an efficient white-light emission by understanding and tuning the ultrafast dynamics of STEs in lead-free perovskite NCs. We then present the exciton energy transfer mediated by STEs to provide an efficient thermally activated delayed fluorescence and dopant PL. We also illustrate promising directions for future applications based on STEs. We hope that this Perspective can provide a new viewpoint for researchers to understand the ultrafast dynamics of STEs and promote lead-free perovskite NCs for optoelectronic applications.

Enhanced Direct White Light Emission Efficiency in Quantum Dot Light‐Emitting Diodes via Embedded Ferroelectric Islands Structure

AbstractWhite light emission is of great importance in our daily life as it is the primary source of light indoor and outdoor as well as day and night. Among various materials and lighting technologies, intensive efforts have been made to quantum dots based‐light‐emitting diode (QD‐LEDs, or QLEDs) because of outstanding optical properties, facile synthesis, and bandgap tunability of QDs. Despite the fact that QLEDs are able to present various colors in a visible range, realizing efficient direct white light emission is a challenge as white light emission can only be achievable through stacking and patterning of QD films or mixing of different sizes of QDs. This inevitably involves energy band mismatch at interfaces, leading to degradation of device performance. Here, a new effective method to improve white QLED performances through embedding a ferroelectric islands structure is introduced, which induces an electric field to effectively modulate the energy band at the junction interface. The formation of a favorable energy landscape leads to efficient charge transport, improved radiative recombination, and consequently high external quantum efficiency in the white QLEDs. In addition, it is demonstrated that this new approach is proved to be effective in different color temperatures ranging from 3000 to over 120 000 K.

Doped all-inorganic cesium zirconium halide perovskites with high-efficiency and tunable emission

Doping enables manipulation of both the electrical and optical properties of halide perovskites. Herein, we incorporated Te4+ into Cs2ZrCl6 single crystal, simultaneously preserving the vacancy-ordered structure, to obtain an efficient yellow-emitting perovskite with a near-unity photoluminescence quantum yield (PLQY ≈ 97.6%). Te4+ doping modifies the hue and emission color of pristine Cs2ZrCl6, generates new absorption channels, and successfully extends the excitation energy from < 280 nm to 360–450 nm range. Detailed spectral characterizations, including ultrafast femtosecond transient absorption measurements, reveal that the bright yellow light is derived from triplet self-trapped excitons. Moreover, further tuning doping concentration enables Te-doped Cs2ZrCl6 single crystals to exhibit efficient warm white light emission. This work provides a new perspective for the development and design of stable lead-free perovskites with highly efficient luminescence.

Surface related laser induced white emission of Cr:YAG ceramic

In this work we report the white light emission in transparent Cr:YAG ceramic pellet upon irradiation with focused beam of CW infrared laser diode. It was found that this phenomenon is specifically related to interaction of laser beam with a surface of the pellet. The white light was emitted outside an irradiated spot at the surface of the pellet and did not penetrate inside the pellet. Moreover, the red emission related to two-photon absorption along the laser beam penetrating the Cr3+:YAG pellet was observed. Interaction of the laser beam with the surface of the pellet leads to an efficient white light emission from an outer side of the pellet. The resulting white light emission did not entry back the pellet. Multiphoton ionization leading to intervalence charge transfer followed by light emission was proposed as the mechanism of experimentally observed white light emission.

A luminescent metal–organic framework with mixed-linker strategy for white-light-emitting by iridium-complex encapsulation

A luminescent MOF [(Zn4O)(L)(2,6-naphthalic acid)]·4H2O·DMF (JLNU-7, JLNU = Jilin Normal University, H4L = methanetetra(tetrakis[4-(carboxyphenyl)oxamethyl]-methane acid) has been hydrothermally synthesized and carefully characterized. The prepared JLNU-7 displayed permanent porosity in the air. Here we select a reasonable strategy to achieve efficient white-light emission by the combination of blue emission from JLNU-7 and yellow emission from [Ir(ppy)2(bpy)][PF6] (IrIII, Hppy = 2-phenylpyridine, bpy = 2,2ʹ-bipyridine). The blue-emitting JLNU-7 was synthesized as a platform for encapsulating yellow-emitting IrIII complex, namely IrIII@JLNU-7. IrIII@JLNU-7 displays white light emission with Commission International de I’Eclairage (CIE) coordinate of (0.323, 0.298) and high quantum yield up to 11.9%. This strategy may promote the development and application of white phosphors with high performance in the practical lighting.

Efficient Regulation of Energy Transfer in a Multicomponent Dye-Loaded MOF for White-Light Emission Tuning.

Owing to their rich porosity and structural diversity, metal-organic frameworks (MOFs) offer substantial advantages over other emission sources for the precise design and color regulation of white-light phosphors. However, achieving efficient white-light emission remains a considerable challenge. Herein, we report a strategy to achieve tunable and efficient white-light emission by regulating energy transfer in a multicomponent dye-loaded MOF. An anionic MOF NKU-114 featuring appropriate confined spaces is designed as a host to deliberately encapsulate three red-, green-, and blue-emissive dyes with adaptive spectral overlap, DSM, AF, and 9-AA, respectively, yielding the NKU-114@dyes composites. Integrating the suitable spectral overlap and efficient energy transfer between the dyes and the framework produced a white-light emission material containing the multicomponent dyes NKU-114@DSM/AF/9-AA. The obtained material has a broadband white emission with a high quantum yield (up to 42.07%) and nearly identical CIE coordinates of (0.34, 0.32), and the moderate correlated color temperature and color-rendering index value can reach up to 5101 K and 81, respectively, suggesting the potential of the multicomponent dye-loaded MOF for white-light-emitting phosphors with good color quality.

White Light Emission by Simultaneous One Pot Encapsulation of Dyes into One-Dimensional Channelled Aluminophosphate.

By simultaneous occlusion of rationally chosen dyes, emitting in the blue, green and red region of the electromagnetic spectrum, into the one-dimensional channels of a magnesium-aluminophosphate with AEL-zeolitic type structure, MgAPO-11, a solid-state system with efficient white light emission under UV excitation, was achieved. The dyes herein selected—acridine (AC), pyronin Y (PY), and hemicyanine LDS722—ensure overall a good match between their molecular sizes and the MgAPO-11 channel dimensions. The occlusion was carried out via the crystallization inclusion method, in a suitable proportion of the three dyes to render efficient white fluorescence systems by means of fine-tuned FRET (fluorescence resonance energy transfer) energy transfer processes. The FRET processes are thoroughly examined by the analysis of fluorescence decay traces using the femtosecond fluorescence up-conversion technique.

Growth mechanism and vibrational and optical properties of SrMoO4: Tb3+, Sm3+ particles: green–orange tunable color

A SrMoO4 series co-doped with Tb3+ and Sm3+ was successfully prepared by the sonochemical method. The particles were characterized by X-ray diffraction, Raman spectroscopy, field emission gun scanning electron microscopy, UV–Vis spectroscopy and photoluminescence. Changes in SrMoO4: Tb3+, Sm3+ morphologies were observed from an orderly growth of the particles. The mechanism of particle growth was proposed, indicating a hierarchical evolution of SrMoO4: Tb3+, Sm3+ morphologies. The changes in emissions were evaluated by the effect of the dopants and their concentrations. Emissions were observed in white, green and orange according to the chemical composition of the samples. The SrMoO4 and SrMoO4: 1% Sm samples showed excellent results for CRI (79%) and LE (> 310 lm/Wopt), thus indicating a material with potential for efficient white light emission.

Enhancement of luminescence properties of SrAl2Si2O8: Eu3+ red phosphor

Aluminosilicate phosphors have been widely used in the fields of fluorescence and laser technology due to its excellent optical properties. However, red phosphors have low luminescence efficiency, and poor physicochemical stability, which cannot achieve efficient white light emission. Therefore, improving the luminescence performance of aluminosilicate red phosphors is a research hotspot in white LED. In this work, SrAl2Si2O8: Eu3+ red phosphor was synthesized by high temperature solid-phase method. By introducing charge compensator and flux, the luminescence intensity of the phosphor is increased. The best charge compensator is determined as Li+ with the same Eu3+ doping content. The best flux is H3BO3, and the optimal doping concentration of flux is 3 wt%. For SrAl2Si2O8: Eu3+, Li+, H3BO3 red phosphor, the CIE coordinates are (0.619, 0.380) and CCT is 3417 K, which is very close to the standard red light. Through LED packaging mixing phosphor with YAG: Ce3+, the method can significantly improve the color rendering index of WLED, up to 84.7. When the temperature reaches 150 °C, the luminescence intensity decreases to 88.02% of the initial value, which indicates that the SrAl2Si2O8 phosphor is an excellent stable red luminescent material.