Junbiao Peng

Europium complexes as emitters in organic electroluminescent devices

Abstract Using two different trivalent europium (Eu 3+ ) complexes, europium(dibenzoylmethanato) 3 (bathophenanthroline) [Eu(DBM) 3 bath] and europium (dibenzoylmethanato) 3 (monophenanthroline) [Eu(DBM) 3 phen], with different ligands for emission-layer materials, various types of electroluminescent (EL) devices have been fabricated. Combined with a triphenylamine derivative (TPD) and an oxadiazole derivative (OXD7) as hole-transport-layer materials, two-layer- and three-layer-type devices have been fabricated. We find that these two emission-layer materials have similar EL spectra, but their EL performances are different. The EL capability of the Eu complexes and their carrier-transporting characteristics are largely dependent on the ligands.

Spectrally-narrow blue light-emitting organic electroluminescent devices utilizing thulium complexes

Abstract Organic electroluminescent (OEL) devices with trivalent thulium (Tm 3+ ) complex (Tm(acetylacetonato) 3 (monophenanthroline) [Tm(AcA) 3 phen]) as an emitting layer were fabricated. Double-layer type cells with a structure of glass substrate/indium–tin oxide (ITO)/poly-(vinylcarbazole) (PVK)/Tm complex/Al exhibit blue luminescence when forward bias dc voltage was applied. Spectrally-narrow OEL emission at 482 nm from Tm 3+ ion in Tm complex was observed.

Energy transfer process from polymer to rare earth complexes

Abstract The interaction between poly( N -vinylcarbazole) (PVK) and rare earth (RE) complexes, such as Eu(thenoytrifluoacetonato) 4 -(monopyridinium) (Eu(TTA) 4 Py). Eu(nitrate) 3 (monophenanthroline) (Eu(NO 3 ) 3 phen) and Tb(acetylacetonato) 3 (monophenanthroline) (Tb(AcA) 3 phen), was investigated in solution as well as in films using the photoluminescence (PL) spectrum. In chloroform solution, the fluorescent intensity of the Eu(NO 3 ) 3 phen was enhanced by PVK; however, the fluorescent intensity of the Tb complex was greatly quenched by PVK. Strongly characteristic emissions of Eu 3+ and Tb 3+ were observed in Eu and Tb complex-dispersed PVK films, respectively. The excitation spectra of Eu complex-dispersed PVK films and Tb complex-dispersed PVK film are very similar to that of the pure PVK film, indicating that effective energy transfer occurs from PVK to the RE complexes. Based on the above experimental results, three types of organic electroluminescence (EL) devices with structure of ITO/Eu(NO 3 ) 3 phen:PVK/OXD-7/Al, ITO/Eu(TTA) 4 Py:PVK/OXD-7/Al and ITO/ Tb(AcA) 3 phen:PVK/OXD-7/Al (ITO = indium-tin oxide) were fabricated. Bright red emission can be observed in the first and second devices while bright green light was emitted from the latter device.

Organic electroluminescent devices using terbium chelates as the emitting layers

Abstract Electroluminescent (EL) devices using a ternary terbium complex [Tb(AcA) 3phen] as emitter have been fabricated. When polyvinylcarbazole is used as the hole-transporting layer (HTL), luminance of 210 cd m−2 with pure Tb3+ EL emissions from the devices is achieved.

Electron-transport properties of rare earth chelates in organic electroluminescent devices

Abstract Electron-transporting properties of a series of trivalent rare earth ion (RE 3+ ) complexes in multilayer organic electroluminescent (OEL) devices have been studied. The emitting layer (EML) in the devices consists of trivalent europium (Eu 3+ ) complexes dispersed into PVK [poly( N -vinylcarbazole)] film.

Redistribution of carriers in OEL devices by inserting a thin charge-carrier blocking layer

Abstract By inserting a thin Gd(AcA) 3 phen layer in the electroluminescent devices ITO/Alq/Al and ITO/TPD/Eu(DBM) 3 phen/Alq/Al, the quantum efficiency is increased in both devices and the emission color of the second device is changed. These results are supposed to be due to the carrier-blocking effect of the thin Gd(AcA) 3 phen layer which changes the distribution of electrons and holes in the devices.

Studies on electroluminescence of multilayer Langmuir-Blodgett films

Abstract A multilayer organic thin film electroluminescence (EL) device has been prepared for the first time by fully using the LB film technique. Its basic structure consists of a hole-transport layer of material, 1,10-bistearyl-4,6,13,15-tetraene-18-nitrogencrown-6 (Nc), without fluorescence, an electron-transport layer of material 8-hydroxyquinoline aluminum, (8-Alq), possessing fluorescence. A uniform blue-green emission was observed under DC voltages of 4–23 V. The electrical and optical properties of the device and the EL process are described. A possible explanation for the red shift of the EL spectrum compared with the PL spectrum of 8-Alq is discussed.

A novel oligomer poly (phenylene vinylene) derivative containing oxadiazole segment

A novel oligomer PPV derivative (OPPV) is reported, which is designed to contain the oxadiazole function segment in the main chain. Photoluminescence of the OPPV thin film originates from aggregated states. In a double layer device consisting of poly phenylene vinylene (PPV) and OPPV, emission only from PPV layer was observed and the efficiency of the device was improved by about one order of magnitude compared with the single layer PPV device, this indicates the electron transport characteristic of OPPV. In the OPPV/Tb complex device, OPPV functions as the hole transport layer. A possible explanation is proposed.

Optical configurations for free electron laser resonators with theoretical and numerical simulation

Optical resonator plays a crucial role in the oscillator scheme of Free Electron Laser (FEL). In this paper, the challenges and some issues on the optical configurations for FEL resonators are presented. Firstly, the diffraction loss and power density are calculated during the preliminary parameters design. Then the detuning and alignment issues of the cavity are discussed with theoretical and numerical simulations. To minimize the influence of the harmonics components, the potential solution based on their spatial distributions is also provided.

Effect of TPD:CuPc LB films as electron blocking layer on EL emission

In organic thin film electroluminescence device with ITO/PPV/TPD:CuPc/Alq:DCMl/Al structure, the TPD:CuPc Langmuir-Blodgett (LB) film as electron-blocking layer was inserted between PPV and Alq:DCMl layer. A device without TPD:CuPc layer or a device with monolayer of TPD:CuPc which was applied at higher DC voltage exhibited EL emission from both the PPV and Alq:DCMl layers. Whereas a device with monolayer of TPD:CuPc layer which was applied at lower voltage or a device with double layers of TPD:CuPc had an EL emission only from Alq:DCMl layer implying that the TPD:CuPc layer can effectively block the electrons and the Alq:DCMl electron transport layer worked as the emitting layer. Hence, we can spatially control the recombination zone and obtain different EL emission by adjusting the thickness of carrier blocking layer.