Pure White Light Emission Research Articles

Photoluminescence properties of Tm3+/Tb3+/Sm3+ tri-doped Na5Y9F32 single crystal with high thermal stability for white light-emitting diodes

A novel Tm3+/Tb3+/Sm3+ tri-doped Na5Y9F32 single crystal was synthesized by a modified Bridgman method for the propose of white light emitting diodes. The fluorescence spectra of various Sm3+ ion concentrations and fixed 0.4 mol% Tm3+ and 0.5 mol% Tb3+ were measured and studied systematically excited by near-ultraviolet light of 355 nm. The Sm3+ ion concentration takes apparent effect on the relative intensity of peaks in the visible region and the color coordinate combining from these emission bands. A near pure white light emission with color coordinates (0.3295, 0.3057) and color temperature (5657 K) can be obtained when the concentrations of Tm3+, Tb3+ and Sm3+ ions are 0.4 mol%, 0.5 mol% and 0.8 mol%, respectively. Furthermore, the practical down-conversion internal quantum yield was measured by integrating spheres at about 14.39%. The tri-doped Na5Y9F32 single crystal shows a high thermal stability inferring from the temperature dependent emission in which the integrated emission intensities are reduced only by ∼3% with the increase of temperature from 280 to 450 K. The present results demonstrate that the Tm3+/Tb3+/Sm3+ tri-doped Na5Y9F32 single crystal may provide a promising candidate for white light-emitting diodes, luminescent materials and fluorescent display devices.

Vitamin B6 cofactors conjugated ovalbumin-stabilized gold nanoclusters: Application in alkaline phosphatase activity detection and generating white-light emission

The red-emitting ovalbumin-stabilized gold nanoclusters (OVA@AuNCs) was prepared and applied for the selective detection of vitamin B6 cofactors. The addition of pyridoxal 5′-phosphate (PLP) and pyridoxal perturbed the fluorescence profile of OVA@AuNCs, and showed new emission band respectively at 532 nm and 437 nm due to the formation of Schiff base linkage between the aldehyde group of the cofactors and the free amine groups present in the OVA. Using OVA@AuNCs, the cofactors PLP and pyridoxal can be detected down to 6.14 × 10−7 M and 5.47 × 10−7 M, respectively. Also, the OVA@AuNCs can be mixed with optimized amount of pyridoxal to generate pure white-light emission. Further, considering the catalytic role of the alkaline phosphatase (ALP) in dephosphorylation, the PLP conjugated OVA@AuNCs was applied as a probe to detect ALP activity. The yellow-emitting PLP_OVA@AuNCs turned to pale-white emitting nanoclusters due to the ALP directed catalytic conversion of PLP into pyridoxal. With PLP_OVA@AuNCs, the ALP activity can be detected down to 3.9 U/L. In addition, the fluorescent color changes of PLP_OVA@AuNCs in the presence of varying amounts of the ALP were integrated with smartphone to develop a simple and cost-effective approach for the on-site detection of ALP activity. Finally, the practical utilities of both the fluorimetric and smartphone approaches were validated by quantifying ALP in various environmental and biological samples.

Single-Molecular White-Light Emitters and Their Potential WOLED Applications.

White organic light-emitting diodes (WOLEDs) are superior to traditional incandescent light bulbs and compact fluorescent lamps in terms of their merits in ensuring pure white-light emission, low-energy consumption, large-area thin-film fabrication, etc. Unfortunately, WOLEDs based on multilayered or multicomponent (red, green, and blue (RGB)) emissive layers can suffer from some remarkable disadvantages, such as intricate device fabrication and voltage-dependent emission color, etc. Single molecules, which can emit white light, can be used to replace multiple emitters, leading to a simplified fabrication process, stable and reproducible WOLEDs. Recently, the performance of WOLEDs by using single molecules is catching up with that of the state-of-the-art devices fabricated by multicomponent emitters. Therefore, an increasing attention has been paid on single white-light-emitting materials for efficient WOLEDs. In this review, different mechanisms of white-light emission from a single molecule and the performance of single-molecule-based WOLEDs are collected and expounded, hoping to light up the interesting subject on single-molecule white-light-emitting materials, which have great potential as white-light emitters for illumination and lighting applications in the world.

Color-tunable single-fluorophore supramolecular system with assembly-encoded emission

Regulating the fluorescent properties of organic small molecules in a controlled and dynamic manner has been a fundamental research goal. Although several strategies have been exploited, realizing multi-color molecular emission from a single fluorophore remains challenging. Herein, we demonstrate an emissive system by combining pyrene fluorophore and acylhydrazone units, which can generate multi-color switchable fluorescent emissions at different assembled states. Two kinds of supramolecular tools, amphiphilic self-assembly and γ-cyclodextrin mediated host-guest recognition, are used to manipulate the intermolecular aromatic stacking distances, resulting in the tunable fluorescent emission ranging from blue to yellow, including a pure white-light emission. Moreover, an external chemical signal, amylase, is introduced to control the assembly states of the system on a time scale, generating a distinct dynamic emission system. The dynamic properties of this multi-color fluorescent system can be also enabled in a hydrogel network, exhibiting a promising potential for intelligent fluorescent materials.

Energy transfer and white luminescence in Bi3+/Eu3+ co-doped oxide glasses

Bi3+/Eu3+-doped SiO2–Al2O3–CaO–B2O3–La2O3–K2O glasses were fabricated and the luminescent properties, energy transfer as well as thermal stability were systematically investigated. Under 333 nm light excitation, bluish-green luminescence centered at 480 nm is observed in the obtained Bi3+-doped glass. By co-doped with Eu3+, highly efficient energy transfer process happens from Bi3+ to Eu3+ via a quadrupole-quadrupole interaction. The energy transfer efficiency can reach 86% and the concentration of Eu3+ is not quenched in here. With increasing Eu3+ concentration, tunable luminescence from bluish-green via white to orange-red is realized. Significantly, pure white light emission with CIE coordinates (0.348, 0.333) is obtained when excited by 333 nm light. Temperature-dependent emission spectra present superior color stability in operating temperature lower than 423 K for the prepared glasses. These results indicate that these glasses are potential white light emitting materials for organic-resin-free W-LEDs.

White Light Emission from a Simple Mixture of Fluorescent Organic Compounds

Three fluorescent organic compounds—furocoumarin (FC), dansyl aniline (DA), and 7-hydroxycoumarin-3-carboxylic acid (CC)—are mixed to produce almost pure white light emission (WLE). This novel mixture is immobilised in silica aerogel and applied as a coating to a UV LED to demonstrate its applicability as a low-cost, organic coating for WLE via simultaneous emission. In ethanol solution and when immobilised in silica aerogel, the mixture exhibits a Commission Internationale d’Eclairage (CIE) chromaticity index of (0.27, 0.33). It was observed that a broadband and simultaneous emission involving coumarin carboxylic acid, furocoumarin and dansyl aniline played a vital role in obtaining a CIE index close to that of pure white light.

Trichromophore-doped cassava-based biopolymer as low-cost and eco-friendly luminous material for bio hybrid white-light-emitting diodes by dual-FRET process

White-light-emitting diodes (WLEDs) are promoted as environmentally friendly because they are energy saving-features and mercury-free aspects, but, rare-earth-free, metal-free, cost-competitive, and eco-friendly for brighter WLEDs are attractive but quite challenging in practice. This paper reports a new methodology using biopolymer luminous material in bio hybrid white-light-emitting diodes (Bio-HWLEDs) based on a trichromophore-doped cassava crystalline thick film that emits bright white light emission through a dual Fӧrster resonance energy transfer (FRET) process. The dual-FRET takes place from coumarin to sulforhodamine via the curcumin chromophore. The Bio-HWLED showed color co-ordinates (0.33, 0.32) that exactly matched with pure white light emission. The effect of temperature on luminescence and the activation energy for thermal quenching were determined using the temperature-dependent photoluminescence measurements. Moreover, Bio-HWLED showed a low luminous drop rate of 0.00069 s−1 to overcome the aggregation-induced quenching effect. These results pave the way towards the realization of commercially viable, large-scale and high-contrast bio hybrid light applications that are environmentally friendly.

In Situ Photoconversion of Multicolor Luminescence and Pure White Light Emission Based on Carbon Dot-Supported Supramolecular Assembly.

Constructing multicolor photoluminescence materials that allow for the integration of suitable external stimuli in order to control luminescence color conversions is a challenging objective. Multicolor luminescent output that is regulated in an in situ photo-controlled manner is not a common phenomenon. Herein, a photoluminescent supramolecular assembly, prepared in two stages, is described that displays in situ photo-tuning broad-spectrum output. Benefiting from the reversible photo-switched constitutional interconversion of diarylethenes, the fluorescence of a guest molecule, styrylpyridinium-modified diarylethene, can be switched on/off by alternating ultraviolet and visible light irradiation. Upon complexation of this guest with a host, cucurbit[8]uril, the fluorescence intensity of the resulting binary supramolecular nanofiber shows a drastic enhancement when compared with that of the free guest, which can also be quenched and recovered reversibly by light irradiation. Significantly, such cationic supramolecular nanofibers also interact with anionic carbon dots to form broad-spectrum output ternary supramolecular assemblies, the fluorescence of which can be changed efficiently from yellow to blue in an in situ photo-controlled manner. Pure white light emission can be realized expediently in the luminescence color-conversion process. The use of light as an external stimulus to regulate fluorescent color conversion provides us with an opportunity to design and construct more advanced anti-counterfeiting materials as well as visual display instruments.

Multicolor Emission from Non‐conjugated Polymers Based on a Single Switchable Boron Chromophore

Multicolor emissive and responsive materials are highly attractive owing to their potential applications in various fields, and polymers are preferred for their good processability and high stability. Herein, we report a series of new polymers based on a methacrylate monomer containing a switchable boron chromophore. In spite of their unconjugated nature, interestingly, the homopolymers from this monomer display rare multicolor fluorescence in solution that is highly dependent on the degree of polymerization (DP). With an increasing DP, the local concentration of the chromophore increases, leading to a higher propensity for switching the blue-emitting tricoordinate boron chromophore to the red-emitting tetracoordinate one. The homopolymers also display temperature- and solvent-dependent emission color change. Furthermore, pure white-light emission could be achieved in various solvents by precisely tuning the homopolymer molecular weight, or in films/solid state by copolymerizing the emissive boron monomer with non-emissive monomers in an appropriate ratio.

Energy transfer and color‐tunable emission in Ba2Y2Si4O13:Bi3+,Eu3+ phosphors

AbstractSingle‐composition Ba2Y2Si4O13:Bi3+,Eu3+ (BYSO:Bi3+,Eu3+) phosphors with color‐tunable and white emission were prepared by conventional high temperature solid‐state reaction method. The structural and luminescent properties of these phosphors were thoroughly investigated through X‐ray diffraction, photoluminescence, and decay curves. BYSO:Bi3+ phosphors show two excitation peaks at 342 and 373 nm, and give two emission peaks at 414 and 503 nm, respectively, indicating that there are two sites of Bi3+ in BYSO. The energy transfer from Bi3+ to Eu3+ was investigated in detail. Varied hues from blue (chromaticity coordinate [0.219, 0.350]) to white (0.288, 0.350) and orange‐red light (0.644, 0.341) can be generated by adjusting the content of Eu3+. Pure white light emission (0.311, 0.338) can be obtained under the excitation of 355 nm in BYSO:3%Bi3+,20%Eu3+ phosphor. Besides, BYSO:Bi3+,Eu3+ phosphors exhibit distinct thermal quenching properties, whose emission intensity at 473 K is 82.6% of that at 298 K. Our results indicate that BYSO:Bi3+,Eu3+ may be applied as conversion phosphors for n‐UV‐based W‐LEDs.

Nanovesicular MOF with Omniphilic Porosity: Bimodal Functionality for White-Light Emission and Photocatalysis by Dye Encapsulation

A new π-chromophoric and asymmetric bola-amphiphilic oligo-( p-phenylene ethynylene)-based tetracarboxylate (OPE-TC1) linker was designed, synthesized, and self-assembled with Zn(OAc)2. The resulting nanoscale metal-organic framework (MOF) {Zn2(OPE-TC1)} n (NMOF-1) showed a vesicular morphology and permanent porosity with omniphilic pore surface. NMOF-1 showed cyan emission with high quantum efficiency (49%). The omniphilicity of the pore was utilized to incorporate ambipolar dye sulforhodamine G (SRG) to tune the band gap as well as to get pure white-light emission. Furthermore, the polar pore surface of NMOF-1 allowed facile diffusion of the substrate for efficient photocatalytic activity. The dye-encapsulated framework further showed enhanced dihydrogen production by 1.75-fold compared to that from the as-synthesized NMOF-1 because of the modulated band gap and high excited state lifetime. As a control experiment, we have synthesized a MOF (MOF-OMe) with an OPE-TC2 linker having -OMe functional groups that did not show nanoscale architecture. This suggested the important role of unsymmetrical bola-amphiphilicity in nanostructuring. This rational design of a chromophoric linker resulted in a nanoscale MOF with omniphilic porosity to achieve bimodal functionality in clean energy applications.

Tricolor White-Light-Emitting Carbon Dots with Multiple-Cores@Shell Structure for WLED Application.

The past few years have witnessed the rapid development of carbon dots (CDs) due to their outstanding optical properties and a wide range of applications. However, the design and control of CDs with long-wavelength multicolor emission are still huge challenges to be addressed for their practical use in different fields. Here, novel nitrogen-doped multiple-core@shell-structured AC-CDs with tricolor emissions of red, green, and blue were constructed via one-pot hydrothermal method from 5-amino-1,10-phenanthroline and citric acid as reactants and the growth process of AC-CDs was monitored with the reaction time in the synthetic system. The origin of different fluorescence emissions was explored using the unique coordination ability of the surface groups of AC-CDs. An obvious concentration dependence of fluorescent properties was observed for the as-prepared AC-CDs, and a highly fluorescent quantum yield (QY) of 67% for red emission at 630 nm can be obtained by adjusting concentration of AC-CDs. The pure white-light emission (0.33, 0.33; Commission Internationale de l'Elcairage coordinate) was carried out from single carbon dot with QY of 29% through regulation of the excitation and concentration of multiple-core@shell-structured AC-CDs. In addition, because of their excellent photoluminescent properties, the white-emitting AC-CDs as emitting phosphor can be easily used in the fabrication of white-light-emitting diode with good anti-photobleaching and temperature stability.

Flux influenced morphology tailoring and emission color tuning to pure white in ZrO2:Eu3+phosphors

Influence of volatile fluxes like NH4Cl, B(OH)3 and their combination on the photo luminescence and morphological properties of ZrO2:Eu3+ phosphor was investigated. The samples were characterized by XRD, UV–visible spectroscopy, scanning electron microscopy and photoluminescence spectra. XRD pattern shows that the samples prepared using ammonium chloride and by combination of ammonium chloride, boric acid crystallizes in tetragonal phase, whereas samples prepared without flux and using boric acid, crystallizes in cubic phase. The results revealed that particle size, morphology, phase and photoluminescence emission color were largely influenced by the flux. Type of flux employed significantly influenced the morphology and emission color of the phosphor. Addition of two fluxes resulted in pure white-light emission, with CIE chromaticity coordinates of (0.327, 0.331), which is very close to the essential requirement to the NTSC (National Television System Committee) system for standard white light.

Self-assembly of emissive supramolecular rosettes with increasing complexity using multitopic terpyridine ligands

Coordination-driven self-assembly has emerged as a powerful bottom-up approach to construct various supramolecular architectures with increasing complexity and functionality. Tetraphenylethylene (TPE) has been incorporated into metallo-supramolecules to build luminescent materials based on aggregation-induced emission. We herein report three generations of ligands with full conjugation of TPE with 2,2′:6′,2″-terpyridine (TPY) to construct emissive materials. Due to the bulky size of TPY substituents, the intramolecular rotations of ligands are partially restricted even in dilute solution, thus leading to emission in both solution and aggregation states. Furthermore, TPE-TPY ligands are assembled with Cd(II) to introduce additional restriction of intramolecular rotation and immobilize fluorophores into rosette-like metallo-supramolecules ranging from generation 1–3 (G1−G3). More importantly, the fluorescent behavior of TPE-TPY ligands is preserved in these rosettes, which display tunable emissive properties with respect to different generations, particularly, pure white-light emission for G2.

Pure white light emission from a rare earth-free intrinsic metal–organic framework and its application in a WLED

Designing of a white light emitting diode based on rare earth metal free intrinsic Zn-MOF by fabricating a suitable device.

Color tuning and white light emission by codoping in isostructural homochiral lanthanide metal-organic frameworks.

Four lanthanide-based homochiral metal–organic frameworks (Ln-HMOFs), {[Ln2(HL)2(H2O)4]·2Cl·5H2O}n [Ln = Gd (1), Eu (2), Tb (3) and Dy (4)], have been synthesized through solvothermal reactions of chiral ligand (S)-5-(((1-carboxyethyl)amino)methyl)isophthalic acid (H3L) with corresponding LnCl3·6H2O. They are binodal (3,6)-connected frameworks with kgd nets based on binuclear cluster units and zwitterionic (HL)2− linkers. Considering the isostructuralism of these Ln-HMOFs as well as the blue emission of compound 1 and the strong typical Eu3+ and Tb3+ emissions of compounds 2 and 3, single-phase mixed-lanthanide HMOFs have been prepared by doping of Ln3+ into the Ln-HMOFs to modulate light-emitting color. Interestingly, the bimetallic doped Eu/Tb-HMOFs [(EuxTb1−x)2(HL)2(H2O)4]·2Cl·5H2O display a fluent change of light-emitting color among green, yellow, orange, orange-red, and red by adjusting the doping concentration of Eu3+ ions into the Tb-HMOF. Very importantly, the trimetallic doped Eu/Gd/Tb-HMOF [(Eu0.1388Gd0.6108Tb0.2504)2(HL)2(H2O)4]·2Cl·5H2O emits white light upon excitation at 355 nm, whose emission can also be switched between different colors when excited with different ultraviolet light. Furthermore, the fluorescence response of Tb-HMOF to various usual metal ions, and especially fluorescent sensing behaviours to Fe3+, Cr3+ and Al3+ have been preliminarily investigated.

Secondary inner filter effect allows extremely efficient pure white light emission by spatially separated organic fluorophores

Efficient white light emission (WLE) using a combination of organic fluorophores requires careful modulation of their distance and orientation. We exploited the secondary inner filter effect (sIFE) between a multi-responsive 2-(1-pyrenyl)benzimidazole (PyBIM) and perylene-monoimide (PMI) secondary emitter to obtain pure WLE (CIE coordinates 0.33, 0.33) with an unsurpassed efficiency of 70 ± 3% under ambient conditions in highly diluted conditions. The sIFE based approach allows extremely efficient WLE using simple fluorophores that are spatially separated.

Efficient pure white light emission based on a three-component La:Eu,Tb-doped luminescent lanthanide metal–organic framework

A three-component Eu and Tb-doped La complex based on a semirigid tricarboxylate ligand is successfully constructed with high-efficiency white light emission (Φ = 11.22% at 345 nm).

Ag nanocluster-based color converters for white organic light-emitting devices

The authors present Ag nanocluster-based color converters (Ag NC color converters), which convert part of the blue light from a light source to yellow light so as to create white organic light-emitting devices that could be suitable for lighting systems. Ag NCs synthesized by poly(methacrylic acid) template methods have a statistical size distribution with a mean diameter of around 4.5 nm, which is larger than the Fermi wavelength of around 2 nm. Hence, like free electrons in metals, the Ag NC electrons are thought to form a continuous energy band, leading to the formation of surface plasmons by photoexcitation. As for the fluorescence emission mechanism, the fact that the photoluminescence is excitation wavelength dependent suggests that the fluorescence originates from surface plasmons in Ag NCs of different sizes. By using Ag NC color converters and suitable blue light sources, white organic light-emitting devices can be fabricated based on the concept of light-mixing. For our blue light sources, we used polymer light-emitting electrochemical cells (PLECs), which, like organic light-emitting diodes, are area light sources. The PLECs were fabricated with a blue fluorescent π-conjugated polymer, poly[(9,9-dihexylfluoren-2,7-diyl)-co-(anthracen-9,10-diyl)] (PDHFA), and a polymeric solid electrolyte composed of poly(ethylene oxide) and KCF3SO3. In this device structure, the Ag NC color converter absorbs blue light from the PDHFA-based PLEC (PDHFA-PLEC) and then emits yellow light. When the PDHFA-PLEC is turned on by applying an external voltage, pure white light emission can be produced with Commission Internationale de l'Eclairage coordinates of (x = 0.32, y = 0.33) and a color rendering index of 93.6. This study shows that utilization of Ag NC color converters and blue PLECs is a very promising and highly effective method for realizing white organic light-emitting devices.

An Acid-Responsive Single Trichromatic Luminescent Dye That Provides Pure White-Light Emission.

A novel acid‐responsive single trichromatic luminescent dye capable of emitting pure white light (WL) is reported. A newly designed p‐phenylene‐bridged bipyrrole bearing N‐alkylimino groups (1 a) specifically provides WL emission upon mixing with trifluoroacetic acid (TFA) in a CH2Cl2 solution. The emission originates from the trichromatic luminescent behavior of 1 a upon protonation of the imino groups. The blue‐light‐emitting 1 a exhibits dramatic color changes in fluorescence to orange and green upon mono‐ and diprotonation, respectively, providing a wide emission band in the range of λ=400–800 nm that provide WL when the compound is in a dynamic equilibrium between the three states. The sample also exhibits low self‐absorption of the emitted light and a high fluorescence quantum yield upon excitation with UV light.