Exciplex formation and electroluminescent absorption in ultraviolet organic light-emitting diodes

We investigated the formation of exciplex and electroluminescent absorption in ultraviolet organic light-emitting diodes（UV OLEDs） using different heterojunction structures.It is found that an energy barrier of over 0.3 eV between the emissive layer（EML） and adjacent transport layer facilitates exciplex formation.The electron blocking layer effectively confines electrons in the EML,which contributes to pure UV emission and enhances efficiency.The change in EML thickness generates tunable UV emission from 376 nm to 406 nm.In addition,the UV emission excites low-energy organic function layers and produces photoluminescent emission.In UV OLED,avoiding the exciplex formation and averting light absorption can effectively improve the purity and efficiency.A maximum external quantum efficiency of 1.2%with a UV emission peak of 376 nm is realized.

An Organic Quantum-Well Electroluminescent Device with Enhanced Performance

An organic electroluminescent (EL) device has been constructed with a double quantum-well structure consisting of N, N'-bis-(1-naphthl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) as a potential well and emitter, and undoped NPB as a barrier potential. The maximum ELefficiency and brightness reach 5.6cd/A and 40000cd/m^(2), respectively. Most importantly, with the increase of the drive voltage, the EL efficiency (cd/A) declines very slowly after reaching its maximum, almost independent of the drive voltage in a wide range from 5 to 13 V. This characteristic may be useful in the improvement of the lifetime of the device.

Synthesis and Color-tunable Fluorescence Properties of Schiff Base Zinc (II) Complexes Used as Electroluminescent Materials

Four kinds of bis(N-alkylsalicylaldiminato) zinc(II) complexes were synthesized, and their molecular structures were determined by FT-IR and elemental analysis. Their photoluminescence properties were determined, which indicated that they could emit strong fluorescence varying from blue to yellow to reddish orange depending on their different molecular structures. They had good thermostability, solubility and film forming capability, and can be used as organic lectroluminescent materials. These new complexes may afford the feasibility to realize full-color display with materials based on similar molecular structures.

Fabrication of Green Electroluminescent Devices

A gadolinium ternary complex, tris(1 phenyl 3 methyl 4 isobutyryl 5 pyrazolone) (2, 2′ dipyridyl) gadolinium Gd(PMIP) 3(Bipy) was synthesized and used as a light emitting material in the organic electroluminescent devices. The devices exhibited the green electroluminescent (EL) emission peaking at 513 nm, originating from the Gd(PMIP) 3(Bipy). By improving the configuration, the device with a structure of ITO/poly(N vinylcarbazole) (PVK) (40 nm)/Gd(PMIP) 3(Bipy) (40 nm)/tris (8 hydroxyquinoline) aluminum (ALQ) (40 nm)/Mg∶Ag(200 nm)/Ag(100 nm) showed higher performance and a maximum luminance of 340 cd·m -2 at 18 V.

Organic Thin Film Electroluminescent Passive Matrix Display

Long life green emitting matrix display based on organic light emitting diode is reported. The pixel number is 96×60, equivalent pixel size 0.4×0.4 mm 2, and the pixel gap 0.1 mm. An image with no crosstalk between pixels is obtained. The average luminance of these pixels at duty cycle of 1/64 is 100 cd/m 2, and the power consumption is 0.6 W. The dark room contrast of 1∶100 is achieved without using a polarization filter.

Influence of the Energy Level Matching on the Performances of Organic/Polymeric Electroluminescent Devices

The performances such as the operating-voltage and the brightness of three types of devices: single-layer device, double-layer device and three-layer device, were examined. It is demonstrated that the I-V characteristics of single-layer device depends not on the applied voltage but instead on the electric-field strength, and the brightness increased by a factor of 50 and the operating-voltage decreased when introducing one electron transporting layer or an electron transporting layer and one hole blocking layer between the light emitting layer and the negative electrode. In fact, it is imperative to match the energy level of each layer in the electroluminescent device in order to improve its comprehensive performances.

Blue-Green Electroluminescent Diodes Utilizing Tris (8-Quinolinolato)-Aluminum Doped Poly (Vinylcarbazole)

Blue-green electroluminescent diodes utilizing tris(8-Quinolino1ato)-aluminum doped poly(vinylcarbazole)have been demonstrated.A Schottky-type electroluminescent diode of the polymer film is driven at 20V and has a peak emission wavelength of 490nm at room temperature with lifetime up to 4 h.

A Successive Scans Method of Adjusting Scan-Time for Injection Electroluminescent Display Panels

Aiming at the problem of luminance uniformity for injection electroluminescent display panels,we present a new scan method for display panels according to successive scans theory.First,on the basis of the number of pixels requiring light emitting in one frame period,we adjust the scan time for each row.Secondly,for ensuring image transmission synchronization,the frame period must to be a constant.We adopt a 64×32 LED display panel as an example to expound the new scan method and we obtain the good result that the reduce amplitude of luminance non-uniformity is 31.34%and the increase amplitude of the average luminance value is 7.8258%.

Blue Electroluminescent Devices Using the Dye Doped Polymers as Emitter and the Organic Molecule Film as Hole Blocking Layer

By placing a hole blocking layer between the polymer and the metallic electrode,we have achieved improved efficiencies for blue electroluminescent devices fabricated with poly(N-vinylcarbazole)doped with 1,1,4,4,-tetraphenyl-1,3-butadiene as the emitter layer and with aluminum and indium/tin-oxide as the electron and hole injecting electrodes.This bilayer device yields bright blue emission having intensity of 300cd/m^(2),in same case the devices without hole blocking layer have luminance of only 44 cd/m^(2).

A New Distyrylarylene Derivative Used as Blue Light Emitter in Organic Electroluminescent Device

A new blue electroluminescent material, distyrylarylene(DSA) derivative, 4,4' bis[2,2 (1 naphthyl,phenyl)vinyl] 1,1' biphenyl(NPVBi) is designed and synthesized. The DSA derivative shows better thermal stability because of its high glass transition temperature. A blue organic light emitting diode(OLED) with the structure ITO/TPD/NPVBi/Alq/LiF/Al is studied. The electroluminescent(EL) spectrum of the OLED exhibits that light emission originates from NPVBi with a peak at 460 nm, its Commission Internationale de l'Eclairage(CIE) color coordinates are x=0.16, y=0.15, and showing independence of CIE color coordinates on current density. The new DSA derivative is expectable as a new candidate for blue light emitter in OLEDs.

Green Light-Emitting Organic Electroluminescent Device with a New Fluorescent Dye Dispersed in Poly(N-vinylcarbazole) Emitter Layer

Double-layer organic electroluminescent devices have been constructed. A new fluorescent dye, 9,10-bis(phenylethynyl)anthracence, was chosen as the dopant which was molecularly dispersed in the polymer film, and green light was observed from the device with luminance of 130cd/m(2) at 17V.

A Stable Blue Organic Electroluminescent Material

In order to compare two kinds of blue electroluminescent materials, we have investigated two kinds of blue OLEDs with the similar structrue ITO/CuPc/NPB/JBEM: perylene/Alq/Mg:Ag [device(J)] and ITO/CuPc/NPB/DPVBi: perylene/Alq/Mg:Ag [device(D)]. The difference of luminance and efficiency was not obvious for the two devices. However, there was remarkable difference for their lifetime. The device(J) achieved longer half lifetime of 1035 h at initial luminance of 100 cd/m 2, and that of device(D) was only 255 h. According to their energy level diagrams , the difference of their stability may originate from different host materials in the two devices. It may be attributed to the better thermal stability of JBEM molecules than that of DPVBi. It is shown that JBEM may be a promising blue organic electroluminescent material with great stability.

Design and Synthesis of a Highly Stable Six-hydrogen-bonded Serfassembly Yellowish Green Electroluminescent Molecular Duplex

This paper describes the design, synthesis and characterization of a hydrogen-bonded molecular duplex with 1,8-naphthalimide fluorescent pendants. The two oligoamide molecular strands, with complementary hydrogen bond sequences of DDADAA and AADADD, can form an ultra stable self-assembly duplex. Its molecular structure was confu-med by ^1H NMR and ESI-MS, and its photoluminescence properties were determined. The resulting duplex exhibited a dramatically enhanced photoluminescence （PL） quantum efficiency of 63.7% compared to the corresponding 1,8-naphthalimide segment （32.4%）, suggesting that the formation of the duplex with larger molecular weight could successfully inhibit the quenching of the fluorescent pendant. This novel duplex is a prospective candidate for new electroluminescent emitter.

Bright Red Organic Electroluminescent Devices Based on a Soluble Rare Earth Complex Eu(TTA)_3 Phen

An Electroluminescent device with PVK film doped with Eu(TTA)_(3) Phen and PBD was fabricated.The device structure of glass substrate/indium tin oxide/PPV/PVK∶Eu(TTA)3 Phen∶PBD/Alq_(3)/Al was employed.A sharply red electroluminescence with a maximum luminance of 56.8 cd/m^(2)at 48 V was achieved.

Photoluminescent and Electroluminescent Properties of Ligand Emitting Y^(3+), La^(3+), Gd^(3+) and Lu^(3+) Complexes

The photoluminescent (PL) and electroluminescent (EL) properties of a series of ligand emitting rare earth complexes (including Y^(3+), La^(3+), Gd^(3+) and Lu^(3+)) were systematically studied. These complexes have the same anionic ligand, 1-phenyl-3-methyl-4-isobutyryl-5-pyrazoloneate (PMIP), and three neutral ligands, triphenyl phosphine oxide (TPPO), 2, 2′-dipyridine (Bipy) and phenanthroline (Phen). Measured with 60 nm thin film of these complexes vaporized in vacuum on quartz substrates, a good regularity in the PL properties was observed. For rational comparison, the same structural EL devices based on these complexes, ITO/PVK (40 nm)/the complex (80 nm)/Mg: Ag (200 nm)/Ag (100 nm), were fabricated. Excluding the exciplex emission happens, the EL luminance usually increases with the increasing of PL efficiency.

SYNTHESIS OF POLY(2,5-DIPHENYL-1,3,4-THIADIAZOLYL)-4,4'-VINYLENE AND ITS ELECTROLUMINESCENT PERFORMANCE

The synthesis, characterization and electroluminescence performance of a new type of conjugatedpolymer, poly(2,5-diphenyl-1,3,4-thiadiazolyl)-4,4'-vinylene (TPPV) are presented. A light-emitting diodeconsisted of ITO/TPPV/Al is driven at about 4.0 V and has a peak emission wavelength of 485 nm. Thisblue-shift of the peak is due to the decrease of conjugate degree of TPPV compared to PPV. This result is inaccord with that determined by XPS and theoretical model of MNDO/3

Electroluminescent Property of A Novel Co-Doped Rare Earth Complex

A novel co-doped rare earth complex Gd0.5Eu0.5（TTA）3Dipy was synthesized and chosen as the emitter material in the organic electroluminescent device ITO/PVK：Gd0.5 Eu0.5 （TTA）3Dipy/PBD/A1. It was proved that there was Forster energy transfer from Gd^3＋ to Eu^3＋. The electroluminescent mechanism of the device was proposed by measuring and analyzing the emission and the excitation spectra of the emissive layer. Gd^3＋ might play the role of promoting the en- ergy transfer from PVK to Eu^3＋ and inhibiting an intrinsic luminescence of PVK. The device displayed red light with good monochromaticity. The possible energy transfer process of the device was preliminarily discussed.

Study of Electroplex Emission from Organic Electroluminescent Devices with Rare Earth Complex

A novel organic electroluminescent device was made with the structure of ITO/PVK：Tb0.5Eu0.5（TTA）3 Dipy/ BCP/Alq3/Al（a） which utilized the rare earth complex Tb0.5Eu0.5（TTA）3 Dipy as the emitting layer. When it was driven under a direct electric field, 612 nm emission from EU^3＋ and 410 nm emission from PVK were observed. In addition, in the EL spectrum a new peak at 490 nm appeared. From the analysis of different devices, the mechanism of the new emission was studied. It was concluded that the new emission was the electroplex originating from the interface between the ligand （TTA）3Dipy and BCP.

Optical Properties, Electronic Energy Level Structure and Electroluminescent Characteristics of Salicylaldehyde Anil Zinc

A new electroluminescent material, salicylaldehyde anil zinc （SAZ） was synthesized, which can form high quality, thermal stability, nano-scale amorphous films by vacuum evaporation. Its structure, thermal stability were characterized by infrared （IR） spectra, differential thermal analysis-thermogravimetry （DTA-TG） analysis, respectively. The optical properties of SAZ were investigated by UV absorption spectra, Photoluminescence （PL） excitation and emission spectra. The highest occupied molecular orbits （HOMO）, lowest unoccupied molecular orbits （LUMO） and optical band gap were evaluated by cyclic voltammetry curve and optical absorption band edge. The electroluminescent devices using SAZ as the emissive layer emit green light with a peak wavelength at 509 nm and a brightness of about 3.1 cd/m^2.