Wenlian Li

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.

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.

Organic Light-Emitting Diode Using Eu3+ Polymer Complex as an Emitter

A new fluorescent Eu3+ polymer complex with the trivalent europium (Eu3+) ion directly bonded to a polymer chain was synthesized, and a new organic electroluminescent (EL) device in which it is used as the emitting layer was fabricated successfully for the first time. It was found that the EL and PL spectra of the device and its film were different from each other; for the former, the emission peaks lie at 595 nm and 657 nm, while it is at 618 nm for the latter. The difference between EL and PL was also discussed.

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.

Effect of Duty Ratio of Driving Voltage on the Forming Process in Aging of Organic Electroluminescent Device

An interesting phenomenon forming process, namely, the rising process of luminance and efficiency at the initial aging of organic eletroluminescent devices, was studied under constant pulse voltage excitation with different duty ratios. The device has a conventional double-layer structure. Tris(8-quinolinolato) aluminum (Alq) was used as the emitter layer, and poly(N-vinylcarbazole) (PVK) was used as the hole transport layer (HTL). The increase of luminance is due to that of the current. It was assumed that the forming process results from the redistribution of the electric field in the organic layer due to the build up of space charge at the interfaces as well as other factors.

Multiphonon Raman scattering in ZnSe/Zn0.80Cd0.20Se superlattices

Abstract A study of the multiphonon (MP) Raman scattering in ZnSe Zn 0.80 Cd 0.20 Se superlattices has been performed for the first time. Two kinds of longitudinal optical phonon modes were observed under the excitation of the 457.9 nm (2.71 eV) and 488.0 nm (2.54 eV) lines of an Ar+ ion laser at room temperature. A systematic discussion to distinguish the MP Raman scattering from hot luminescence is presented.

Photoluminescence of ZnSe/Zn1 − xCdxSe strained superlattices under hydrostatic pressure

Abstract A study of the photoluminescence (PL) of ZnSe/Zn 1 − x Cd x Se strained superlattices under hydrostatic pressure (0–2.5 GPa) at room temperature has been performed for the first time. The small sublinear dependence of PL energy with pressure for the heavy-hole exciton of the well layers was observed. The pressure coefficients of the PL peak were obtained by least-squares fits to the experimental data. The linear pressure coefficient obtained by calculation is in good agreement with the experimental one.

Rare-earth chelate phosphors for organic EL devices

The electroluminescence (EL) of the Tb complex [Tb(ACA) 3 phen] and the Eu complex [Eu(TTA) 3 (TPPO) 2 ] used for organic LEDs was investigated, and a luminance of 210 cd/m 2 with sharp green bands for the organic LEDs containing Tb(II was achieved. It was found that the EL properties of the devices using the Tb complex as the emitter depend on the hole-transporting layers. We have also noticed that the Tb complex plays an electron-transporting-layer role when the device has the ITO/Eu complex/Tb complex/Al structure.

Studies on synthesis and EL properties of several novel squaraines

Abstract Several novel squaraines were synthesized and their structures were elucidated by IR, HNMR, MS and elementary analysis. Their photoluminescent (PL) and electroluminescent (EL) properties have been studied, which indicated that all of them had electrontransporting properties, and some had both electron, and hole-transporting properties. One of the squaraines was inserted between a cathode and an anode, and the single-layer-sandwiched device processed a redlightemitting ability under both low negative and low positive driven bias. It was regarded as one kind of promising material.

EXCITONIC PROPERTIES OF ZNSE-ZNCDSE MULTIPLE-QUANTUM WELLS UNDER HIGH-EXCITATION DENSITY

ZnSe-Zn0.78Cd0.22Se MQWs are grown on GaAs(100) substrate by MOCVD. The photoluminescence (PL) under pulsed N2 laser excitation is investigated in detail. The bands observed in PL spectra at 77K are attributed to the n = 1,2 heavy-hole exciton transitions, respectively. In high-density excitation the excitonic recombination is mainly on the exciton interaction, involves the exciton-electron (Ex-x) and exciton-exciton (Ex-Ex) interactions. The stimulated emission due to Ex-Ex scattering is observed at 77K in ZnSe-ZnCdSe MQWs.