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By doping red dye 4-dicyanomethylene-2-(tert-butyl)-6-methyl-4H-pyran(DCJTB) in the tris-(8-hydroxyquinolinato) metal Mq3(where M=Al, Ga, In) chelate complexes, a series of red-dopant organic light-emitting diodes with different doping concentrations have been fabricated. The electroluminescence efficiency of these red diodes with a DCJTB doped Mq3 emitting layer is found to be decreased markedly with the increasing of doping concentration. Electroluminescence characteristics of these devices are studied in terms of energy levels matching of red-dopant with the host materials and carrier transporting layers.

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/m2, 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.

Rubrene was doped into the hole transport layer of an organic thin film electroluminescent (OTFEL) device with a double-layered structure. It was found that the dopant has a profound influence on the EL characteristics - it changed the region of light emission, increased the luminescence efficiency by more than 50% and improved the device stability tenfold. The reasons for these effects are discussed based on injection theory and the energy level diagram of the device.

Copper phthalocyanine(CuPc) thin film layer was inserted between the anode indium tin oxide and the hole transport layer TPD of an organic thin film electroluminescent device with a double-layered structure. It is found that the CuPc layer greatly improves the device stability. The durability of the device with CuPc layer increases about 8 times. The fact that at a constant current density the driving voltage remains unchanged with operation time for the device with CuPc layer means that the barriers of the carriers injection are stable due to the inserted CuPc layer.

Some organic thin film electroluminescent (EL) devices with aluminium-doped zinc oxide as the hole-injecting electrode have now been manufactured. Their EL spectra and J - V and B - V characteristics have been studied in detail. The work function and ionization potential of the materials composing the devices have been measured and their energy models given. The EL performance properties have been explained well.

Blue emitting electroluminescent diode using PVCz doped with perylene and BBOT as electron transport has been constructed. The emission spectrum is a mixture of spectra of BBOT and perylene. A luminance of as high as 680 cd/m2 with lumen efficiency more then 0.028 lm/W have been obtained.

The impact excitation rates, and consequently the emission intensities, of various energy states of Tm3+ in ZnS thin-film electroluminescence (TFEL) have been quantitatively evaluated by calculating the radiative transition rates and the impact cross section, together with a Baraff distribution function of hot-electron energy. The results show that the direct impact excitation rate of the 1G4 state of Tm3+ is very small, while that of the 3F4 state is fairly large, resulting in a weak blue light intensity relative to the IR light in TFEL. Different theories of the electron distribution function are compared and discussed.

A simplified quantitative physical model for electron transport processes in TFEL is proposed. The dissipative current, brightness waveform and charge voltage characteristics of the device can be calculated from this model. Comparison of the computer simulation with the exerimental results shows that this model is nearly satisfactory. Hence some important parameters of these devices can be obtained by computer simulation.

Energy transfer between in N , N ′-bis-(1-naphthyl)- N , N ′-diphenyl-1,1′-biphenyl-4-4′-diamine (NPB) and rubrene was investigated. The device ITO/CuPc/NPB:rubrene/blocking layer /Alq/MgAg, in which copper phthalocyanine (CuPc) is used as buffer layer, NPB as the hole transporting layer (HTL), trimer of N -arylbenzimidazoles (TPBi) [or 2–(4–biphenylyl)–5–(4–tertbutylphenyl)–1,2,3–oxadiazole(PBD) or 1,2,4–triazolederivative(TAZ)] as the blocking layer, Tris(8-quinolinolato)aluminum complex (Alq) as electron transporting layers (ETL), can not give white emitting light. White emitting light can be realized in a new device with the structure ITO/CuPc/NPB/blocking layer:rubrene/Alq/MgAg, in which rubrene is doped in blocking layer instead of in NPB. The emission spectrum of this device covers a wide range of visible region and can be adjusted by the concentration of rubrene. The white emitting devices with CIE coordinates x =0.31, y =0.32, maximum luminance 8635 cd/m 2 and luminous efficiency 1.39 Lm/w, were obtained with the blocking layer TPBi doped with 1.5% rubrene.

We demonstrate a highly efficient inverted top-emitting organic light-emitting diode (TOLED) having stable electroluminescent spectra and color coordination with variation of viewing angles by simply tuning the resonance wavelength corresponding to the free emission of the emitter. Using a doped fluorescent emitting system, the inverted TOLED exhibits an enhanced maximum current efficiency of 19 cd/A and a power efficiency of 17 lm/W, which are much higher than those (11 cd/A and 5 lm/W) of the counterpart with normal structure, although both TOLEDs behave with similar stable electroluminescent spectra characteristics. The results indicate that we provide a simple and effective method of constructing an excellent inverted TOLED for potentially practical applications.

Multicomponent excited-state emissions from monomer, exciplex and electroplex were observed in a bilayer organic electroluminescent device with a structure of ITO/TPD(60nm)/PBD(60nm)/Al(where TPD and PBD stand for N,N′diphenylN,N′bis(3-methylphenyl)1,1′biphenyl4,4′diamine) and (2(4′biphenyl)5(4″tertbutylphenyl)1,3,4oxadiazole, respectively). The difference between the photoluminescence of this device and the TPD∶PBD equimolar evaporated films suggests that the exciplex takes place only at the interface of TPD/PBD. The Variation of electroluminescence spectra with bias indicates the different formation mechanisms and the different population of each excited state component, as well as the different dynamic recombination process of carriers in this device.

The effect of electric field on the luminescence and exciton in polymer is studied in two aspects: 1. In strong electric field, the exciton is dissociated into a pair of positive and negative polarons. This dissociation can quantitatively indicate the electric-field-induced luminescence quenching in electroluminescent polymer m-LPPP observed recently. 2. The π electrons in polymer possess delocalization, they are easily polarized. It is shown that the exciton in polymer has huge polarizability, which is 103 times larger than that of hydrogen atoms.