White Electroluminescence from a Phosphonate-Functionalized Single-Polymer System with Electron-Trapping Effect

A novel strategy for obtaining white electroluminescence (EL) is based on the mechanism of electron trapping on host. Phosphonate-functionalized polyfluorene is chosen as host owing to its strong electron affinity. Electrons are confined mostly by host pendants in the EL process, which suppresses charge transfer from host to dopant. White EL with CIE coordinates of (0.34,0.35) is achieved.

Controllable Red, Green, Blue (RGB) and Bright White Upconversion Luminescence of Lu2O3:Yb3+/Er3+/Tm3+ Nanocrystals through Single Laser Excitation at 980 nm

Lu2O3:Yb3+/Er3+/Tm3+ nanocrystals have been successfully synthesized by a solvothermal process followed by a subsequent heat treatment at 800 degrees C. Powder X-ray diffraction, transmission electron microscopy, upconversion photoluminescence spectra, and kinetic decay were used to characterize the samples. Under single-wavelength diode laser excitation of 980 nm, the bright blue emissions of Lu2O3:Yb3+, Tm3+ nanocrystals near 477 and 490 nm were observed due to the (1)G(4)-> H-3(6) transition of Tm3+. The bright green UC emissions of Lu2O3:Er3+ nanocrystals appeared near 540 and 565 nm were observed and assigned to the H-2(11/2)-> I-4(15/2) and S-4(3/2)-> I-4(15/2) transitions, respectively, of Er3+. The ratio of the intensity of green luminescence to that of red luminescence decreases with an increase of concentration of Yb3+ in Lu2O3:Er3+ nanocrystals.

Structural and Bluish-White Luminescent Properties of Li+-Doped BPO4 as a Potential Environmentally Friendly Phosphor Material

Many efforts have been devoted to exploring novel luminescent materials that not contain expensive or toxic elements, or do not need a mercury vapor plasma source. In this paper, BPO4 and Li+-doped BPO4 powder samples were prepared by the Pechini-type sol-gel (PSG) process. The structure and optical properties of the resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), photoluminescence (PL) excitation and emission spectra, kinetic decay, and X-ray photoelectron spectra (XPS), respectively. It was found that PSG -derived Li+-doped BPO4 annealed at 960 degrees C exhibited bright bluish-white emission centered at 416 nm. The luminescence decay curves analysis indicates that each sample has two kinds of lifetimes (5.9 ns and 0.529 ms) and two types of kinetic decay behaviors which can be fitted into a single-exponential function and a double-exponential function, respectively.

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.

Sol-gel derived Y2O3 as an efficient bluish-white phosphor without metal activator ions

In this paper, Y2O3 powder phosphors without metal activators were successfully prepared by the sol-gel method. The obtained sample shows an intense bluish-white emission (ranging from 350 to 600 nm, centered at 416 nm) under a wide range of UV light excitation (235-400 nm). The chromaticity coordinates of the sample are x = 0.159, y = 0.097, and the quantum yield is as high as 64.6%, which is a high value among the phosphor family without metal activators. The luminescent mechanisms have been ascribed to the carbon impurities in the Y2O3 host.

Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism Analysis

By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C-2']picolinate (Flrpic) for blue emission and bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1 H-benzoimidazol-N,C-3) iridium(acetylacetonate) ((fbi)(2)Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5 lm W-1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8 cd A(-1). Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density-voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of Flrpic and (fbi)(2)Ir(acac) are, respectively, host-guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses.

Highly efficient single-emitting-layer white organic light-emitting diodes with reduced efficiency roll-off

By codoping blue and orange phosphorescent dyes into a single host material, a highly efficient white organic light-emitting diode (WOLED) with Commission Internationale de L'Eclairage coordinates of (0.38, 0.43) at 12 V is demonstrated. Remarkably, this WOLED achieves reduced current efficiency roll-off, which slightly decreases from its maximum value of 37.3-31.0 cd/A at 1000 cd/m(2). The device operational mechanism is subsequently investigated in order to unveil the origin of the high performance.

High efficiency fluorescent white organic light-emitting diodes with red, green and blue separately monochromatic emission layers

Highly efficient fluorescent white organic light-emitting diodes (WOLEDs) have been fabricated by using three red, green and blue, separately monochromatic emission layers. The red and blue emissive layers are based on 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) doped N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and p-bis(p-N,N-diphenyl-amino-styryl) benzene (DSA-ph) doped 2-methyl-9,10-di(2-naphthyl) anthracene (MADN), respectively; and the green emissive layer is based on tris(8-hydroxyquionline)aluminum(Alq(3)) doped with 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl- 1H,5H,1[H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-1]-one (C545T), which is sandwiched between the red and the blue emissive layers. It can be seen that the devices show stable white emission with Commission International de L'Eclairage coordinates of (0.41, 0.41) and color rendering index (CRI) of 84 in a wide range of bias voltages.

A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer

By utilizing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline:Li/MoO3 as an effective charge generation layer (CGL), we extend our recently demonstrated single-emitting-layer white organic light-emitting diode (WOLED) to realize an extremely high-efficiency tandem WOLED. This stacked device achieves maximum forward viewing current efficiency of 110.9 cd/A and external quantum efficiency of 43.3% at 1 mu A/cm(2) and emits stable white light with Commission Internationale de L'Eclairage coordinates of (0.34, 0.41) at 16 V. It is noted that the combination of effective single units and CGL is key prerequisite for realizing high-performance tandem WOLEDs.

Achieving highly efficient white organic light-emitting diodes with reduced efficiency roll-off

A highly efficient and colour-stable three-wavelength white organic light-emitting diode with the structure of indium tin oxide (ITO)/MoO3/N,N'-diphenyl-N,N'-bis (1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB)/4,4'-N,N'-dicarbazole-biphenyl (CBP): bis(2,4-diphenylquinolyl-N,C-2') iridium( acetylacetonate) (PPQ)(2)Ir(acac)/NPB/p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph):2-methyl-9,10-di(2-naphthyl) anthracene (MADN)/tris (8-hydroxyquinoline) aluminum (AlQ): 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)/AlQ/LiF/Al is fabricated and characterized. A current efficiency of 12.3 cdA(-1) at an illumination-relevant brightness of 1000 cd m(-2) is obtained, which rolls off slightly to 10.3 cdA(-1) at a rather high brightness of 10 000 cd m(-2). We attribute this great reduction in the efficiency roll-off to the wise management of singlet and triplet excitons between emissive layers as well as the superior charge injection and diffusion balance in the device.

Multifunctional bipolar triphenylamine/oxadiazole derivatives: highly efficient blue fluorescence, red phosphorescence host and two-color based white OLEDs

Two simple triphenylamine/oxadiazole derivatives were synthesized and fully characterized; their multifunctionality as highly efficient non-doped blue fluorescence, excellent red phosphorescent host and single-doped two-color based white OLEDs has been demonstrated.

Sr3Al2O5Cl2:Ce3+,Eu2+: A potential tunable yellow-to-white-emitting phosphor for ultraviolet light emitting diodes

The Sr3Al2O5Cl2:Ce3+,Eu2+ phosphors were prepared by solid state reaction. The obtained phosphors exhibit a strong absorption in the UV-visible region and have two intense emission bands at 444 and 609 nm. The energy transfer from the Ce3+ to Eu2+ ions was observed, and the critical distance has been estimated to be about 24.5 A by spectral overlap method. Furthermore, the developed phosphors can generate lights from yellow-to-white region under the excitation of UV radiation by appropriately tuning the activator content, indicating that they have potential applications as an UV-convertible phosphor for white light emitting diodes.

Synergetic Effect of Efficient Energy Transfer and 3D pi-pi Stack for White Emission Based on the Block Copolymers Containing Nonconjugated Spacer

A series of block copolymers containing nonconjugated spacer and 3D pi-pi stacking structure with simultaneous blue-, green-, and yellow-emitting units has been synthesized and characterized. The dependence of the energy transfer and electroluminescence (EL) properties of these block copolymers on the contents of oligo(phenylenevinylene)s has been investigated. The block copolymer (GEO8-BEO-YEO4) with 98.8% blue-emitting oligomer (BEO), 0.8% green-emitting oligomer (GEO), and 0.4% yellow-emitting oligomer (YEO) showed the best electroluminescent performance, exhibiting a maximum luminance of 2309 cd/m(2) and efficiency of 0.34 cd/A. The single-layer-polymer light-emitting diodes device based on GEO2-BEO-YEO4 emitted greenish white light with the CIE coordinates of (0.26, 0.37) at 10 V. The synergetic effect of the efficient energy transfer and 3D pi-pi stack of these block copolymers on the photoiuminescent and electroluminescent properties are investigated.

White light emission from Eu3+ in CaIn2O4 host lattices

CaIn2O4:xEu(3+) (x=0.5%,1.0%,1.5%) phosphors were prepared by the Pechini sol-gel process [U.S. Patent No. 3,330,697 (1967)] and characterized by x-ray diffraction and photoluminescence and cathodoluminescence spectra as well as lifetimes. Under the excitation of 397 nm ultraviolet light and low voltage electron beams, these phosphors show the emission lines of Eu3+ corresponding to D-5(0,1,2,3)-F-7(J) (J=0,1,2,3,4) transitions from 400 to 700 nm (whole visible spectral region) with comparable intensity, resulting in a white light emission with a quantum efficiency near 10%. The luminescence mechanism for Eu3+ in CaIn2O4 has been elucidated.

Efficient multilayer white polymer light-emitting diodes with aluminum cathodes

Efficient multilayer white polymer light-emitting diodes (WPLEDs) with aluminum cathodes are fabricated. The multilayer structure is composed of a water soluble hole-injection layer, a toluene-soluble emissive layer, and an alcohol-soluble emissive layer. The polarity difference of the solvents used for spin coating these polymers allows for realization of the multilayer polymer structure. The recombination zone confined at the interface of the two emissive polymers avoids exciton quenching by electrodes, and white emission is realized by harvesting photons emitted from the two emissive polymers. A maximum luminous efficiency of 16.9 cd/A and a power efficiency of 11.1 lm/W are achieved for this WPLED.