Realization of blue, green and red emission from top-emitting white organic light-emitting diodes with exterior tunable optical films

We developed an approach to realize blue, green and red emission from top-emitting white organic light-emitting diodes (OLEDs) through depositing exterior tunable optical films on top of the OLEDs. Three primary colors for full color display including blue, green and red emission are achieved by controlling the wavelength-dependent transmittance of the multilayer optical films overlaid on the emissive layer.

Simultaneous blue, green, and red emission from diblock copolymer micellar films: a new approach to white-light emission

White-light emission is achieved from a single layer of diblock copolymer micelles containing green- and red-light-emitting dyes in the separate micellar cores and blue-light-emitting polymer around their periphery, in which fluorescence resonance energy transfer between fluorophores is inhibited due to micelle isolation, resulting in simultaneous emission of these three species.

Molecular design on highly efficient white electroluminescence from a single-polymer system with simultaneous blue, green, and red emission

A highly efficient white electroluminescent polymer with simultaneous blue, green, and red emission is reported, developed using a dopant/host strategy by covalently attaching both a green- and a red-light-emitting dopant to the side chain of a blue-light-emitting polymer host (see figure). In a single-layer device a maximum luminance efficiency of 7.3 cd A(-1) with CIE coordinates of (0.31,0.32) is achieved.

Tuning the saturated red emission: synthesis, electrochemistry and photophysics of 2-arylquinoline based iridium(III) complexes and their application in OLEDs

A series of novel iridium(III) complexes with two 2-arylquinoline derivatives as cyclometalated ligands and one monoanionic ligand, such as acetylacetonate (acac), N,N'-diethyldithiocarbamate (Et(2)dtc) and O,O'-diethyldithiophosphate (Et(2)dtp), as ancillary ligands have been synthesized and structurally characterized by H-1 NMR, MS and elemental analysis (EA). The cyclic voltammetry, absorption, emission and electroluminescence properties of these complexes were systematically investigated. Through extending pi-conjugation, introducing electron-donating groups in the ligand frame, or changing the ancillary ligands, the HOMO energy levels of the iridium(III) complexes can be tuned, while their LUMO levels remain little affected; in consequence, the emission wavelengths of the iridium(III) complexes can be tuned in the range 606-653 nm. The highly efficient organic light-emitting diodes (OLEDs) with saturated red emission have been demonstrated. A maximum current efficiency of 10.79 cd A(-1), at a current density of 0.74 mA cm(-2), with an emission wavelength of 616 nm and Commisioon Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which are very close to the National Television System Comittee (NSTC) standard red emission, have been achieved when using complex (DPQ)(2)Ir(acac) as a phosphor dopant.

Two-photon excited red upconversion luminescence of thulium ions doped GeS2-In2S3-CsI glass

We report a novel phenomenon in GeS2-In2S3-CsI chalcohalide glass doped with Tm3+ ions. Under irradiation with an 808 nm laser diode, a bright red emission centered at 700 nm is observed for the first time in this glass. The log-log correlation between integrated emission intensity and pump power reveals that a two-photon absorption process is involved in the phenomenon, suggesting that the F-3(3,2) -> H-3(6) transition of Tm3+ ions is responsible for the appearance of the red emission. The results indicate that the indium (In) based chalcohalide glass containing Tm3+ ions is expected to find applications in visible lasers, high density optical storage and three-dimensional color displays. (C) 2009 Elsevier B.V. All rights reserved.

Full-color emission from In2S3 and ln(2)S(3): Eu3+ nanoparticles

New observations on the luminescence Of In2S3 and europium-doped In2S3 nanoparticles show a green (5 10 nm) emission from In2S3 and In1.8Eu0.2S3 nanoparticles while a blue (425 nm) emission is observed from ln(1.6)Eu(0.4)S(3) nanoparticles. Both the blue and green emissions have large Stokes shifts of 62 and 110 nm, respectively. Excitation with longer-wavelength photons causes the blue emission to shift to a longer wavelength while the green emission wavelength remains unchanged. The lifetimes of both the green and blue emissions are similar to reported values for excitonic recombination. When doped with Eu3+, in addition to the broad blue and green emissions, a red emission near 615 nm attributed to Eu3+ is observed. Temperature dependences on nanoparticle thin films indicate that with increasing temperature, the green emission wavelength remains constant, however, the blue emission shifts toward longer wavelengths. Based on these observations, the blue emission is attributed to exciton recombination and the green emission to Indium interstitial defects. These nanoparticles show full-color emission with high efficiency, fast lifetime decays, and good stability; they are also relatively simple to prepare, thus making them a new type of phosphor with potential applications in lighting, flat-panel displays, and communications.

Highly efficient red electroluminescent polymers with dopant/host system and molecular dispersion feature: polyfluorene as the host and 2,1,3-benzothiadiazole derivatives as the red dopant

By selecting polyfluorene as the polymer host, choosing 2,1,3-benzothiadiazole derivative moieties as the red dopant units and covalently attaching 0.3 mol% of the dopant units to the side chain of the polymer host, we developed a novel series of red electroluminescent polymers of dopant/host system with molecular dispersion feature. Their EL spectra exhibited predominant red emission from the dopant units because of the energy transfer and charge trapping from the polymer backbone to the dopant units. The emission wavelength of the polymers could be tuned by modifying the chemical structures of the dopant units.

Improved color purity and efficiency by a coguest emitter system in doped red light-emitting devices

We demonstrate red organic light-emitting diodes (OLEDs) with improved color purity and electroluminescence (EL) efficiency by codoping a green fluorescent sensitizer 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1, 1, 7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-ij)quinolizin-11-one (C545T) as the second dopant and a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the lumophore into tris(8-hydroquinoline) aluminum (Alq(3)) host. It was found that the C545 T dopant did not by itself emit but assisted the carrier trapping from the host Alq(3) to the red emitting dopant. The red OLEDs realized by this approach not only kept the purity of the emission color, but also significantly improved the EL efficiency. The current efficiency and power efficiency, respectively, reached 12 cd/A at a current density of 0.3 mA/cm(2) and 10lm/W at a current density of 0.02 mA/cm(2), which are enhanced by 1.4 and 2.6 times compared with devices where the emissive layer is composed of the DCJTB doped Alq(3), and a stable red emission (chromaticity coordinates: x = 0.64, y = 0.36) was obtained in a wide range of voltage. Our results indicate that the coguest system is a promising method for obtaining high-efficiency red OLEDs.

Efficient red organic light-emitting diodes based on a dinuclear europium complex

Pure red organic light-emitting diodes based on a dinuclear europium complex with a structure of (TTA)(3)Eu(PYO)(2)Eu(TTA)3 (TTA = thenoyltrifluoroacetonate, PYO = pyridine N-oxide) were presented. The devices showed pure red emission at a peak wavelength of 612 nm with a full width at half maximum of 3 nm, which is a characteristic emission from Eu3+ ion based on D-5(0) -> F-7(2) transition. The maximum brightness and electroluminescent (EL) efficiency reached 340 cd/m(2) at a driving voltage of 19 V and 2.4 cd/A (0.78 lm/W) at a current density of 0.14 mA/cm(2), respectively.

White electroluminescence from a single-polymer system with simultaneous two-color emission: Polyfluorene as blue host and 2,1,3-benzothiadiazole derivatives as orange dopants on the side chain

Four single polymers with two kinds of attachment of orange chromophore to blue polymer host for white electroluminescence (EL) were designed. The effect of the side-chain attachment and main-chain attachment on the EL efficiencies of the resulting polymers was compared. The side-chain-type single polymers are found to exhibit more efficient white EL than that of the main-chain-type single polymers. Based on the side-chain-type white single polymer with 4-(4-alkyloxy-phenyl)-7-(4-diphenylamino-phenyl)-2,1,3-benzothiadiazoles as the orange-dopant unit and polyfluorene as the blue polymer host, white EL with simultaneous orange (lambda(max) = 545 nm) and blue emission (lambda(max) = 432 nm/460 nm) is realised. A single-layer device (indium tin oxide/poly(3,4-ethylenedioxythiophene)/polymer/Ca/Al) made of these polymers emits white light with the Commission Internationale de l'Eclairage coordinates of (0.30,0.40), possesses a turn-on voltage of 3.5 V, luminous efficiency of 10.66 cd A(-1), power efficiency of 6.68 lm W-1, and a maximum brightness of 21240 cd m(-2).

Novel heteroleptic Cu-I complexes with tunable emission color for efficient phosphorescent light-emitting diodes

A series of orange-red to red phosphorescent heteroleptic Cu-I complexes (the first ligand: 2,2 '-biquinoline (bq), 4,4 '-diphenyl2,2 '-biquinoline (dpbq) or 3,3 '-methylen-4,4 '-diphenyl-2,2 '-biquinoline (mdpbq); the second ligand: triphenylphosphine or bis[2-(diphenylphosphino)phenyl]ether (DPEphos)) have been synthesized and fully characterized. With highly rigid bulky biquinoline-type ligands, complexes [Cu(mdpbq)(PPh3)(2)](BF4) and [Cu(mdpbq)(DPEphos)](BF4) emit efficiently in 20 wt % PMMA films with photoluminescence quantum yield of 0.56 and 0.43 and emission maximum of 606 nm and 617 nm, respectively. By doping these complexes in poly(vinyl carbazole) (PVK) or N-(4-(carbazol-9-yl)phenyl)-3,6-bis(carbazol-9-yl) carbazole (TCCz), phosphorescent organic light-emitting diodes (OLEDs) were fabricated with various device structures. The complex [Cu(mdpbq)(DPEphos)](BF4) exhibits the best device performance. With the device structure of ITO/PEDOT/ TCCz:[Cu(mdpbq)(DPEphos)](BF4) (15 wt %)/TPBI/LiF/Al (III), a current efficiency up to 6.4 cd A(-1) with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.61, 0.39) has been realized. To our best knowledge, this is the first report of efficient mononuclear Cu complexes with red emission.

Improved efficiency by a fluorescent dye in red organic light-emitting devices based on a europium complex

By doping a fluorescent dye in the emissive layer, we realized high efficient red organic light-emitting diodes (OLEDs) based on a europium complex. The OLEDs realized by this method showed pure red emission at 612 nm with a full width at half maximum Of 3 nm. The Commission International de L'Eclairage Coordination keeps approximately the same as the emission of pure Eu3+. The maximum brightness and EL efficiency reached 2450 cd/m(2) at 20 V and 9.0 cd/A (6.0 lm/w) at a current density of 0.012 mA/cm(2), respectively. At the brightness of 100 cd/m(2), the current efficiency reached 4.4 cd/A.

Soluble, saturated-red-light-emitting poly(p-phenylenevinylene) containing triphenylamine units and cyano groups

A conjugated poly(p-CN-phenylenevinylene) (PCNPV) containing both electron-donating triphenylamine units and electron-withdrawing cyano groups was prepared via Knoevenagel condensation in a good yield. Gel permeation chromatography suggested that the soluble polymer had a very high weight-average molecular weight of 309,000. A bright and saturated red emission was observed under UV excitation in solution and film. Cyclic voltammetry showed that the polymer presented quasi-reversible oxidation with a relatively low potential because of the triphenylamine unit. A single-layer indium tin oxide/PCNPV/Mg-Ag device emitted a bright red light (633 nm).

Monodisperse spherical core-shell structured SiO2-CaTiO3 : Pr3+ phosphors for field emission displays

Nanocrystalline CaTiO3:Pr3+ phosphor layers were coated on nonaggregated, monodisperse, and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2-CaTiO3:Pr3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2-CaTiO3:Pr3+ phosphor particles. The obtained core-shell structured phosphors consist of well dispersed submicron spherical particles with a narrow size distribution. The thickness of the CaTiO3:Pr3+ shell could be easily controlled by changing the number of deposition cycles (about 70 nm for four deposition cycles). The core-shell SiO2-CaTiO3:Pr3+ particles show a strong red emission corresponding to D-1(2)-H-3(4) (612 nm) of Pr3+ under the excitation of ultraviolet (326 nm) and low voltage electron beams (1-5 kV). These particles may be used in field emission displays.

New fluorescent dipolar pyrazine derivatives for non-doped red organic light-emitting diodes

Dipolar fluorescent compounds containing electron-accepting pyrazine-2,3-dicarbonitrile and electron-donating arylamine moiety have been designed and synthesized. The optical and electrochemical properties of these compounds can be adjusted by changing pi-bridge length and the donor (D) strength. Organic light-emitting devices based on these compounds are fabricated. Saturated red emission of (0.67, 0.33) and the external quantum efficiency as high as 1.41% have been demonstrated for one of these compounds.