[Multiplayer white organic light-emitting diodes with different order and thickness of emission layers].

In multilayer OLED devices, the order and thickness of the emission layers have great effect on their spectrum. Based on the three basic colours of red, blue and green, a series of white organic light-emitting diodes(WOLEDS)with the structure of ITO/CuPc(12 nm)/NPB(50 nm)/EML/LiF(1 nm)/Al(100 nm) and a variety of emission layer's orders and thicknesses were fabricated. The blue emission material: 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN) doped with p-bis(p-N, N-diphenyl-amono-styryl)benzene(DSA-Ph), the green emission material: tris-[8-hydroxyquinoline]aluminum(Alq3) doped with C545, and the red emission material: tris-[8-hydroxyquinoline]aluminum( Alq3) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were used. By adjusting the order and thickness of each emission layer in the RBG structure, we got a white OLED with current efficiency of 5.60 cd x A(-1) and Commission Internationale De L'Eclairage (CIE) coordinates of (0. 34, 0.34) at 200 mA x cm(-2). Its maximum luminance reached 20 700 cd x m(-2) at current density of 400 mA x cm(-2). The results were analyzed on the basis of the theory of excitons' generation and diffusion. According to the theory, an equation was set up which relates EL spectra to the luminance efficiency, the thickness of each layer and the exciton diffusion length. In addition, in RBG structure with different thickness of red layer, the ratio of th e spectral intensity of red to that of blue was calculated. It was found that the experimental results are in agreement with the theoretical values.

[Spectrum study on highly saturated blue organic top-emitting devices with microcavity structure].

The blue top-emitting organic light-emitting devices with cavity effect have been fabricated. The authors used the TBADN : 3% DSAPh as emitting material of blue microcavity OLEDs. The devices consisted of Ag/ITO/CuPc/NPB/TBADN : 3% DSAPh/Alq3/LiF/Al(Ag) structure. On a patterned glass substrate, silver was deposited as reflective anode, and copper phthalocyanine (CuPc) layer as HIL and 4'-bis[N-(1-Naphthyl)-N-phenyl-amino] biphenyl (NPB) layer as HTL were made. Aluminum and silver thin films were made as semi-transparent cathode. The transmittance of aluminum and silver (Al/Ag) cathode was about 30%. In EL spectrum, the full width at half maximum (FWHM) was only 17 nm. By changing the thicknesses of ITO, highly saturated color with Commission Internationale de L'Eclairage chromaticity coordinates (CIEx,y) of (0.141, 0.049) was obtained. In the present article, the emission intensity of spectrum was studied. An appropriate cathode transmittance will result in maximal emission intensity. By using the formula of microcavity, the approximative curve that describes the change of emission intensity with cathode transmittance (or reflectance) was figured out.

[Multiple emissions in organic electroluminescent device using a mixed layer as an emitter].

A organic electroluminescent device has been fabricated by using a mixed layer as an emitter. The configuration of the device is ITO/TPD/TPD: PBD(equimole)/PBD/A1, in which TPD (N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine) and PBD (2-(4'-biphenyl)-5-(4''-tert-butylphenyl)-1,3,4-oxadiazole) are used as hole transport material and electron transport material, respectively. Broad and red-shifted electroluminescent spectra related to the fluorescence of constituent materials were observed. It is suggested that the monomer, exciplex and electroplex emissions are simultaneously involved in EL spectra by comparison of the EL with the PL spectra and decomposition of the EL spectrum. The type of exciplex is the interaction between the excited state TPD (TPD*) and PBD in the ground state, and the type of electroplex is a (D+-A-)* complex by cross-recombination of hole on the charged hole transport molecule (D+) and electron on the charged electron transport molecule (A-). All types of excited states show different formation mechanisms and recombination processes under electric field. The change of emission strengths from monomer and excited complexes lead to a blue-shift of the emissive spectra with an increasing electric field. The maximum luminance and external quantum efficiency of this device are 240 cd x (cm2)(-1) and 0.49%, respectively. The emissions from exciplex or electroplex formation at the organic solid interface generally present a broad and red-shifted emissive band, providing an effective method for tuning of emission color in organic electroluminescent devices.

[Luminescence properties of Pr(3+) and energy transfer characteristics of Pr(3+)-->Gd(3+) in CaSiO3].

The excitation spectrum and the emission spectrum of Pr3+ in CaSiO3 under the room temperature were studied. The emission spectrum was constituted of three emission bands, corresponding to the emissions of the lowest 4f5d states to the 3H4, 3H6, 1G4 of the 4f2 states. The emission of the 3P0 and 1D2 were not observed. The concentration quenching of Pr3+ was due to the radiative and nonradiative energy transfer. There was energy transfer from Pr3+ to Gd3+, with the transfer rate of 10% of the Pr3+ emission rate.