Denghui Xu

Organic light-emitting diode with liquid emitting layer

We demonstrate an original organic light-emitting diode (OLED) having a neat liquid host of 9-(2-ethylhexyl)carbazole (EHCz) doped with a guest emitter of 5,6,11,12-tetraphenylnapthacene (rubrene). The device structure is composed of indium tin-oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate)/EHCz:rubrene/Cs2CO3/ITO. We demonstrate that the liquid organic semiconducting layer surely transports charge carriers, leading to electroluminescence from rubrene with the highest external quantum efficiency of ηext=0.03% at a current density of 0.26 mA/cm2. Our demonstration of the liquid-OLEDs will open another possibility of organic semiconductors and light-emitting applications.

Emission Characteristics of PVK Doped TbY(o-MBA)6(phen)2 Systems

Abstract A rare earth complex TbY (o-MBA)6(phen)2 was synthesized, which was first used as an emitting material in electroluminescence. By doping it into the conjugated polymer PVK, single-layer and double-layer devices were fabricated with structures: device A: ITO/PVK: TbY (o-MBA)6(phen)2/BCP/Al; B: ITO/PVK: TbY (o-MBA)6(phen)2/AlQ/LiF/Al; C: ITO/PVK: TbY (o-MBA)6(phen)2/BCP/AlQ/LiF/Al. The characteristics of these devices were investigated. For single-layer and double-layer devices, the emission of PVK was completely restrained, and only the green emission from Tb3+ was observed in electroluminescence. The above mentioned observation is attributed to the different mechanism of electroluminescence and photoluminescence. In photoluminescence process, the energy of Tb complex may come from PVK through Forster energy transfer process, while in electroluminescence process direct sequential charge trapping appeares to be the main operating mechanism. From the optimized device B, brightly green emission can be obtained, and the highest EL brightness of the device reaches 213 cd·m−2 at 14 V.

Quantum well organic light emitting diodes with ultra thin Rubrene layer

Organic light-emitting diodes with ultra thin Rubrene layer have been fabricated with the structure of ITO/hole-transport layer/Rubrene/AlQ/LiF/Al. The hole-transport layer are copper phthalocyanine (CuPc), poly(3,4-ethylenedioxythiophene) doped with polystrenesulphonic acid (PEDOT: PSS), poly(N-vinyl carbazole) (PVK), and N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB), respectively. Compared with the other two devices, when 5,6,11,12-tetraphenylnaphthacene (Rubrene) is inserted between PVK (or NPB) and tris(8-quinolinolato)aluminum (AlQ), Rubrene’s emission get enhanced. The energy transfer mechanism among PVK (NPB), AlQ and Rubrene are revealed by the absorption and emitting spectra. Moreover, the enhancement of Rubrene’s emission can also be ascribed as an organic quantum well structure’s trap effection.

Hydrothermal synthesis and luminescence properties of KLa(MoO4)2:Eu3+ phosphor

Abstract. KLa(MoO4)2:Eu3+ phosphors were prepared by the hydrothermal method. The after tuning of synthesis time and the ratio of the ethylene glycol to water ratio made the phosphor present different morphologies, including peanut-like shape and spheres. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), diffuse reflectance spectrum, and fluorescence spectrum. Under the excitation of 397 nm near-ultraviolet, the typical red emission produced by Eu3+ ions can be observed. And the phosphors show strong red light around 612 nm, attributed to D50→F72 transition of Eu3+ ion. The luminescence properties of the as-prepared phosphors were studied based on changing the synthesis condition. It is found that the synthesis time and the changing of the ratio of ethylene glycol to water play the crucial role in the formation of morphology. The optimum dopant concentration of Eu3+ ions in KLa(MoO4)2:Eu3+ is around 7 mol. %. Moreover, the fluorescence decay curve and thermal stability of luminescence were also investigated in detail. The Commission International de I’Eclairage coordinates of KLa(MoO4)2:0.07Eu3+ located in the red reddish region. All the results suggest that KLa(MoO4)2:0.07Eu3+ might be a promising reddish-orange emitting phosphor used in white light-emitting diodes (w-LED).

Bright red-to-yellow organic light-emitting devices based on polarization-induced spectral shifts and broadening

We demonstrated red and yellow organic light-emitting devices (OLEDs) with the structure of ITO/NPB/AlQ:DCJTB/AlQ/LiF/Al, where the NPB, AlQ and DCJTB are 4, 4′-bis[N-(1-naphthyl)-N-henylamino] biphenyl, tris(8-quinolinolato)aluminum and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, respectively. Electroluminescent (EL) behaviors of these devices have been examined with different concentrations of DCJTB doped into AlQ matrix. The emission color of the devices depends on the doping concentrations of DCJTB. For red and yellow OLEDs, a maximum luminescence of 2750 cd/m2 and 21,700 cd/m2 was obtained, respectively. The peak emission wavelength shift of DCJTB was found to be due to the polarization effects. It is of particular interest that the EL spectrum of DCJTB got broadening with the doping concentrations and current densities of the devices in our experiments.

Organic light-emitting devices based on new rare earth complex Tb(p-CIBA)3phen

A new rare earth complex Tb(p-CIBA)3phen was synthesized and introduced into organic light emitting devices (OLEDs) as emitting material. The Tb(p-CIBA)3phen was doped into PVK to improve the film-forming and hole-transporting property. Two kinds of devices were fabricated. The device structure is as the following. Single-layer device: ITO/PVK: Tb(p-CIBA)3phen/LiF/Al; double-layer device: ITO/PVK: Tb(p-CIBA)3phen/AIQ/LiF/Al. The performances of both devices were investigated carefully. We found that the emission of PVK was completely restrained, and only the green emission was observed from the electroluminescence. The full width at half maximum (FWHM) was less than 10 nm. The highest EL brightness of the single-layer device is 25.4 cd/cm2 at a fixed bias of 18 V, and the highest EL brightness of the double-layer device reaches 234.8 cd/cm2 at a voltage of 20 V.

Electroluminescence Based on Eu0.5La0.5(TTA)3phen Doped Poly N-Vinylcarbazole

Abstract A novel rare earth complex Eu 0.5 La 0.5 (TTA) 3 phen, displaying electroluminescent property, was synthesized, and monolayer and double-layer devices were fabricated by doping it into poly N-vinylcarbazole. The characteristics of these optimized devices were investigated, and the emitting mechanism was explained through the energy band diagram. Optimized double-layer devices with a turn-on voltage of 6.5 V were achieved. At the current density of 68.48 mA·cm −2 , the maximum brightness and the current efficiency of the device reached 238.4 cd·m −2 and 0.35 cd·A −1 , respectively.

Synthesis and Luminescence Properties of Ba 3 Lu(PO 4 ) 3 :Sm 3+

Novel Ba3Lu(PO4)3:Sm3+ phosphors were prepared by solid-state reaction. The results of X-ray diffraction, photoluminescence spectra and decay time spectra suggest that it might be a promising reddish-orange emitting phosphor used in w-LEDs.

The effect of various electrodes on the properties of electroluminescent devices with potassium chloride inside tris (8-hydroxyquinoline) aluminum

The performance of organic light-emitting diodes (OLED), based on NPB/Alq3/KCl/Alq3 active regions, with various anode (i.e. ITO and ITO/MoO3) and cathode (i.e. Al and LiF/Al) structures is compared. NPB, Alq3, KCl, ITO, MoO3, Al and LiF are N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine, tris (8-hydroxyquinoline) aluminum, potassium chloride, indium-tin oxide, molybdenum trioxide, aluminum and lithium fluoride, respectively. When bare Al is used as a cathode, both luminance and efficiency are improved by the insertion of KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/Al), compared to a control device (anode/NPB/Alq3/Al). This is attributed to trap sites induced by KCl layer, which give a better recombination in the devices. However, if the cathode is LiF/Al, the performance of control device (anode/NPB/Alq3/LiF/Al) is superior to that of devices with KCl inside Alq3 (anode/NPB/Alq3/KCl/Alq3/LiF/Al), which is attributed that the probability of electron injection from cathode is decreased.

Theoretical investigation of the fixing phase in two-center holographic recording

The fixing phase of the two-center holographic recording is not consistent with the mono-exponential formula, and the charge-transfer mechanism of the fixing phase is studied theoretically. The electron gratings of the shallower traps center have a great influence on the fixed space-charge-field, the stronger electrons grating of the shallower traps center would enhance the saturation space-charge-field of the deeper traps center in the fixing phase. The effects of the Fe concentration, Cu concentration and the oxidization-reduction state of the crystals on the fixed space-charge-field are investigated by using the Runge-Kutta method. The results show that the higher Fe concentration, the lower Cu concentration and the weakly oxidized crystal are available for enhancing the saturation space-charge-field of the deeper traps center.