Efficient White Light Emission Research Articles

Brightening triplet excitons enable high-performance white-light emission in organic small molecules via integrating n–π*/π–π* transitions

Luminescent materials that simultaneously embody bright singlet and triplet excitons hold great potential in optoelectronics, signage, and information encryption. However, achieving high-performance white-light emission is severely hampered by their inherent unbalanced contribution of fluorescence and phosphorescence. Herein, we address this challenge by pressure treatment engineering via the hydrogen bonding cooperativity effect to realize the mixture of n–π*/π–π* transitions, where the triplet state emission was boosted from 7% to 40% in isophthalic acid (IPA). A superior white-light emission based on hybrid fluorescence and phosphorescence was harvested in pressure-treated IPA, and the photoluminescence quantum yield was increased to 75% from the initial 19% (blue-light emission). In-situ high-pressure IR spectra, X-ray diffraction, and neutron diffraction reveal continuous strengthening of the hydrogen bonds with the increase of pressure. Furthermore, this enhanced hydrogen bond is retained down to the ambient conditions after pressure treatment, awarding the targeted IPA efficient intersystem crossing for balanced singlet/triplet excitons population and resulting in efficient white-light emission. This work not only proposes a route for brightening triplet states in organic small molecules, but also regulates the ratio of singlet and triplet excitons to construct high-performance white-light emission.

White-Emitting Gold Nanocluster Assembly with Dynamic Color Tuning.

We report that constructed Au nanoclusters (NCs) can afford amazing white emission synergistically dictated by the Au(0)-dominated core-state fluorescence and Au(I)-governed surface-state phosphorescence, with record-high absolute quantum yields of 42.1% and 53.6% in the aqueous solution and powder state, respectively. Moreover, the dynamic color tuning is achieved in a wide warm-to-cold white-light range (with the correlated color temperature varied from 3426 to 24 973 K) by elaborately manipulating the ratio of Au(0) to Au(I) species and thus the electron transfer rate from staple motif to metal kernel. This study not only exemplifies the successful integration of multiple luminescent centers into metal NCs to accomplish efficient white-light emission but also inspires a feasible pathway toward customizing the optical properties of metal NCs by regulating electron transfer kinetics.

Tuneable Efficient White Emission of Sb3+/Mn2+ Co-Doped Lead-Free Perovskites for Single-Component White Light-Emitting Diodes.

Inorganic lead-free perovskite nanocrystals (NCs) with broadband self-trapped exciton (STEs) emission and low toxicity have shown enormous application prospects in the field of display and lighting. However, white light-emitting diodes (WLEDs) based on a single-component material with high photoluminescence quantum yield (PLQY) remain challenging. Here, we demonstrate a novel codoping strategy by introducing Sb3+/Mn2+ ions to achieve the tuneable dual emission in lead-free perovskite Cs3InCl6 NCs. The PLQY increases to 59.64% after doping with Sb3+. The codoped Cs3InCl6 NCs exhibit efficient white light emission due to the energy transfer channel from STEs to Mn2+ ions with PLQY of 51.38%. Density functional theory (DFT) calculations have been used to verify deeply the effects of Sb3+/Mn2+ doping. WLEDs based on Sb3+/Mn2+-codoped Cs3InCl6 NCs are explored with color rendering index of 85.5 and color coordinate of (0.398, 0.445), which have been successfully applied as photodetector lighting sources. This work provides a new perspective for designing novel lead-free perovskites to achieve single-component WLEDs.

Phosphor-free micro-pyramid InGaN-based white light-emitting diode with a high color rendering index on a β-Ga2O3 substrate.

We demonstrate the InGaN/GaN-based monolithic micro-pyramid white (MPW) vertical LED (VLED) grown on (-201)-oriented β-Ga2O3 substrate by selective area growth. The transmission electron microscopy (TEM) reveals an almost defect-free GaN pyramid structure on (10-11) sidewalls, including stacked dual-wavelength multi-quantum wells (MQWs). From the electroluminescence (EL) spectra of the fabricated MPW VLED, a white light emission with a high color rendering index (CRI) of 97.4 is achieved. Furthermore, the simulation shows that the light extraction efficiency (LEE) of the MPW VLED is at least 4 times higher compared with the conventional planar LED. These results show that the MPW VLED grown on β-Ga2O3 has great potential for highly efficient phosphor-free white light emission.

Direct White-Light Emitting From a Single Metal-Organic Framework with Dual Phosphorescence Peaks.

Single component white-light-emitting (SCWLE) materials are extremely desired in the field of solid-state lighting. However, pure-phosphorescent SCWLE has rarely been reported. Herein, one halogen-bonding-containing MOF [Cd(5-BIPA)(phen)] (1) has been synthesized, which shows efficient white-light emission originating from dual phosphorescence bands with different wavelengths and lifetimes. The fabrication of a phosphor-converted white-light-emitting diode device driven by pulsing current enables this MOF to be a promising phosphor.

Light‐up the white light emission in microscale with a superior deep‐blue AIE fiber as wave‐guiding source

AbstractThe development of high‐performance organic blue light‐emitting emitters is in urgent to act as an excitation source to contribute the white light generation. On the other hand, the investigation on optical waveguides have been received increasing attentions because they can manipulate the light propagation accurately in the microscale to boost the optoelectronic and energy conversion applications. In this work, we facilely prepared a deep‐blue aggregation‐induced emission (AIE) dye, namely TPP‐4OMe, which shows high luminescent efficiency, narrow emission band and good stability in the aggregate state. TPP‐4OMe can be fabricated as deep‐blue AIE microfibers readily with definite morphology and composition. Based on the AIE microfibers, the active waveguide to transmit deep‐blue emission signals can be achieved with a very low optical loss coefficient (α) of 6.7 × 10−3 dB μm−1. Meanwhile, the full‐visible broadband low‐loss passive waveguide can be well performed with these AIE microfibers, which has never been observed in the pure organic crystals. More interestingly, the excellent properties of AIE microfibers enable them to act as a wave‐guiding excitation source, resulting in a distinct and pure white light emission. The present work not only provides excellent blue light‐emitting materials but also bridges the waveguide to realize the efficient white light emission to accelerate the practical applications.

Silicon-based nanoparticles grafted lanthanide coordination polymer phosphor: Facile synthesis, formation process and white light-emitting diodes

White light-emitting diodes (WLEDs) are promising candidates for environment-friendly solid-state light sources, where modulation of white light has been a significant research priority. Here we achieved a new single-phase white light phosphor (Si NPs-M) by grafting silicon-based nanoparticles onto a red lanthanide coordination polymer by a simple wet chemical method. The activation of the energy transfer mechanism is controlled by changing the local site of ion coordination (by varying the Eu3+ concentration) to achieve modulation of the molecule to fine-tune its emitted chromaticity. The synthesis of a single-phase phosphor based on ultraviolet (UV) pumped and as a WLED was realized. These WLEDs demonstrate white light for color coordinates of (0.3405, 0.3682), CRI of 78, and CCT of 5210 K. In addition, the WLEDs possess good optical stability as the drive current increase from 30 mA to 300 mA, while the phosphor maintains 87.4 % of the luminous intensity when the external temperature rises to 130 °C, indicating high stability. This work has potential applications for silicon-compatible display technologies that require fine control of efficient white light emission.

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er3+, Tm3+ and Yb3+ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm3+1G4→3H6 transition, 531 and 547 nm (green) from the Er3+2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and 640 and 662 nm (red) from the Er3+4F9/2 → 4I15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er2O3, 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3, and this crystal is suitable for use in highly efficient white light emission devices.

Facile Synthesis of Multicolored Stacked Quantum Dot Films for Efficient White Light Emission

Quantum dot (QD)-based white light-emitting diodes (LEDs) or white QD-LEDs were successfully fabricated by stacking QD films of primary colors (i.e., red, green, and blue). An ultrathin ZnO film was deposited between each QD layer to facilitate the formation of a tricolor-stacked QD structure. Such stacked QD films effectively suppress the Förster resonance energy transfer between QDs and enable efficient blue light emission, unlike randomly mixed QD films of different colors. The photoluminescence (PL) spectra of various QD films were obtained to study the change in the corresponding color gamut with applied voltage. In addition, QD-LEDs were fabricated based on the PL behavior and electronic band diagrams of QDs of different colors. Maximum luminance and peak EQE of white QD-LED shows 5700 cd/m2 and 1.1% compared to 2200 cd/m2 and 0.3% of QD-LED with mixed QD layer. Finally, a smooth color transition and white light emission were achieved using a blue/green/red stacking sequence for the QDs, which successfully suppressed the energy transfer effect. The overall performance and brightness of the white QD-LEDs synthesized in this study can be further enhanced by developing high-performance blue QDs.

Efficient White Light Emission of 0D Lead-Free Indium-Based Halide Perovskite and the Intermediate State Promotion Mechanism of the Nonadiabatic Transition to Self-Trapped Exciton via Antimony(III) Cation Doping

Efficient White Light Emission of 0D Lead-Free Indium-Based Halide Perovskite and the Intermediate State Promotion Mechanism of the Nonadiabatic Transition to Self-Trapped Exciton via Antimony(III) Cation Doping

Composition engineering of lead-free double perovskites towards efficient warm white light emission for health and well-being

Lead-free halide double perovskites (DPs) [A2B(I)B(III)X6] (A: monovalent cation, B(I): monovalent cation, B(II): trivalent cation, X: halide anion) has drawn tremendous attention because of their environmental-friendliness and high stability compared to traditional lead-based perovskites ABX3 (A: monovalent cation; B: Pb2+; X: halide anion). The optoelectronic properties of DPs are, however, compromised. This work provides a methodology for improving the photophysical properties of DPs and achieving high-efficiency warm white light emission. First principles density functional theory (DFT) was used in material design and the ligand-free synthesis of halide DP Cs2Ag1−xKxIn0.875Bi0.125Cl6 (x ≤ 0.60) via a facile recrystallization process was demonstrated. The compositional tuning of K+ to Ag+ resulted in an improvement in photophysical properties. Independent of K+ content, all the samples exhibit strong absorption at a wavelength of λmax ∼ 375 nm with a direct bandgap which is consistent with our DFT calculation results. Broadband photoluminescence (PL) emission profiles covering the spectra from blue to deep red (405–820 nm at λmax ∼ 629 nm) were observed. Besides, with an optimized K+ alloying content of 0.20, the optical performance of these halide DPs was impressively regulated, demonstrating improved photoluminescence quantum yield (PLQY) of host Cs2AgInCl6 crystals from ∼ 2.70 % (x = 0) to ∼15.96 % (x = 0.20), due to increased radiative recombination of self-trapped excitons. the highest report for such structures. It also shows high stability over 180 days. Furthermore, the use of blue-emitting CsPbBr3 and DP Cs2Ag0.80K0.20In0.875Bi0.125Cl6 as color conversion layers in white light-emitting diodes (LEDs) demonstrates that high-quality white light emission with the CIE color coordinate of (0.387, 0.385) and a correlated color temperature (CCT) of 3878 K, color rendering index (CRI) of 85, and luminous efficacy of radiation (LER) of 214 lm/W. Hence, the research work provides insight into realizing environmentally friendly and high-efficiency white light emission with high color quality by using earth-abundant elements and the low-cost synthesis method.

Cost-effective way of improving the optical properties of phosphor-in-glass by adjusting the particle size of glass powder

The effects of silicate glass particle size and Y3Al5O12: Ce3+ (YAG: Ce3+) phosphor doping concentration on the optical properties of phosphor-in-glass (PiG) samples were investigated. When the average particle size of glass powder was 160, 100, 60, and 30 μm, the transmittance of silicate glass with a thickness of 0.6 mm was 68%, 78%, 62%, and 54%, respectively. With the mixing of 4 wt% YAG: Ce3+ phosphor in each component of silicate glass, the transmitted luminous flux of PiG gradually increased with the increase of transmittance, reaching a maximum of 179.5 lm. Simultaneously, we found that with the increase in transmittance, the photoluminescence (PL) intensity of PiG gradually decreased; however, the total luminous flux of PiG has independent of transmittance. When the doping concentration of YAG: Ce3+ phosphor was 4 wt%, PiG achieved a maximum efficient white light emission of 212.61 lm/W under blue laser excitation at 2.31 W. All results indicate the outstanding feasibility of the prepared YAG-PiG in high-power/high-brightness white light-emitting diodes (WLEDs).

Dipole plasmon vitalized efficient white light emission via charge transfer in all oxide-based heterojunctions

Solid-state white-light emission, which is rapidly becoming the standard in a wide range of lighting applications, can be regarded as the best possible light source for next-generation cost-effective lighting. Herein, we report a simple solution-based technique to get efficient white-light emission using all-oxide semiconductor-based heterojunction. In this work, vertically oriented CuO nanorods were used for outstanding white-light emission by depositing ZnO thin films over CuO nanorods. The resulted bi-layered ZnO/CuO heterojunction arrangement have shown excellent optoelectronic properties. Furthermore, the inclusion of Au layer between ZnO/CuO heterojunction has improved white-light emission significantly and as an integral, a white light photoluminescence (PL) with a chromaticity coordinate of (0.32, 0.34) was obtained. Ab-initio calculations have supported our mechanism of charge transfer from CuO to ZnO especially with Au insertion. The presented work will provide insights into the intriguing optoelectronic properties of oxide hetero-structures.

Tunable Efficient White Emission in Holmium Doped Double Perovskites Cs2KInCl6 via Antimony Sensitization

AbstractRecently, ns2 metal ions (such as Bi3+ and Sb3+) doped double perovskites have captured intense attention for their efficient emission, however, achieving efficient and tunable white light emission is always an enormous challenge. Herein, Sb3+/Ho3+ co‐doped Cs2KInCl6 double perovskites are proposed, and the photoluminescence results show that there are two emission bands, one broad cyan emission band stems from self‐trapped exciton (STE) in [SbCl6]3‐ octahedron, while another red emission band derives from the f‐f transitions of Ho3+. The emission processes for Sb3+/Ho3+ co‐doped Cs2KInCl6 show that Sb3+ can act as the sensitizer to activate Ho3+ emission, which is due to the energy transfer channel from STE to Ho3+. As the Ho3+ concentration increases, the luminous color of Sb3+/Ho3+ co‐doped Cs2KInCl6 can be modulated from cyan to orange under 315 nm light irradiation, and the white emission can even be obtained with a photoluminescence quantum yield of 90 ± 2% when the energy‐transfer efficiency is 50%. Finally, single compound white‐light emitting diodes and fluorescent anti‐counterfeiting labels based on 0.5%Sb3+/60%Ho3+ co‐doped Cs2KInCl6 are fabricated. This work provides an effective strategy to achieve efficient tunable white emission in lead‐free double perovskites through ns2 metal and lanthanide ion co‐doping.

Highly efficient warm white light emission in Sb3+-doped (NH4)4CdCl6metal halides through A-site Rb-alloying regulation

Novel all-inorganic Sb3+-doped (NH4)4CdCl6metal halides with excellent optoelectronic properties were prepared and efficient single component warm white light emission could be achieved through the A-site Rb alloying.

Efficient single-component white light emitting diodes enabled by lanthanide ions doped lead halide perovskites via controlling Förster energy transfer and specific defect clearance

Currently, a major challenge for metal-halide perovskite light emitting diodes (LEDs) is to achieve stable and efficient white light emission due to halide ion segregation. Herein, we report a promising method to fabricate white perovskite LEDs using lanthanide (Ln3+) ions doped CsPbCl3 perovskite nanocrystals (PeNCs). First, K+ ions are doped into the lattice to tune the perovskite bandgap by partially substituting Cs+ ions, which are well matched to the transition energy of some Ln3+ ions from the ground state to the excited state, thereby greatly improving the Förster energy transfer efficiency from excitons to Ln3+ ions. Then, creatine phosphate (CP), a phospholipid widely found in organisms, serves as a tightly binding surface-capping multi-functional ligand which regulates the film formation and enhances the optical and electrical properties of PeNC film. Consequently, the Eu3+ doped PeNCs based-white LEDs show a peak luminance of 1678 cd m-2 and a maximum external quantum efficiency (EQE) of 5.4%, demonstrating excellent performance among existing white PeNC LEDs from a single chip. Furthermore, the method of bandgap modulation and the defect passivation were generalized to other Ln3+ ions doped perovskite LEDs and successfully obtained improved electroluminescence (EL). This work demonstrates the comprehensive and universal strategies in the realization of highly efficient and stable white LEDs via single-component Ln3+ ions doped PeNCs, which provides an optimal solution for the development of low-cost and simple white perovskite LEDs.

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.