Electrolytic Deposition and Diffusion of Lithium onto Magnesium-9 Wt Pct Yttrium Bulk Alloy in Low-Temperature Molten Salt of Lithium Chloride and Potassium Chloride

The electrolytic deposition and diffusion of lithium onto bulk magnesium-9 wt pct yttrium alloy cathode in molten salt of 47 wt pct lithium chloride and 53 wt pct potassium chloride at 693 K were investigated. Results show that magnesium-yttrium-lithium ternary alloys are formed on the surface of the cathodes, and a penetration depth of 642 mu m is acquired after 2 hours of electrolysis at the cathodic current density of 0.06 A center dot cm(-2). The diffusion of lithium results in a great amount of precipitates in the lithium containing layer. These precipitates are the compound of Mg41Y5, which arrange along the grain boundaries and hinder the diffusion of lithium, and solid solution of yttrium in magnesium. The grain boundaries and the twins of the magnesium-9 wt pct yttrium substrate also have negative effects on the diffusion of lithium.

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis, Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe3+, [Fe(CN)(6)](3-) and KCl. Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe3+ to Fe2+ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer-by-layer technique. The thus-prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H2O2 reduction.

Achieving highly efficient white organic light-emitting diodes with reduced efficiency roll-off

A highly efficient and colour-stable three-wavelength white organic light-emitting diode with the structure of indium tin oxide (ITO)/MoO3/N,N'-diphenyl-N,N'-bis (1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB)/4,4'-N,N'-dicarbazole-biphenyl (CBP): bis(2,4-diphenylquinolyl-N,C-2') iridium( acetylacetonate) (PPQ)(2)Ir(acac)/NPB/p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph):2-methyl-9,10-di(2-naphthyl) anthracene (MADN)/tris (8-hydroxyquinoline) aluminum (AlQ): 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)/AlQ/LiF/Al is fabricated and characterized. A current efficiency of 12.3 cdA(-1) at an illumination-relevant brightness of 1000 cd m(-2) is obtained, which rolls off slightly to 10.3 cdA(-1) at a rather high brightness of 10 000 cd m(-2). We attribute this great reduction in the efficiency roll-off to the wise management of singlet and triplet excitons between emissive layers as well as the superior charge injection and diffusion balance in the device.

Lead(IV) dioxide: an effective electron injection material to realize high-efficiency inverted top-emitting organic light-emitting diodes

Lead(IV) dioxide (PbO2) has been used as the electron injection layer (EIL) to realize high-efficiency inverted top-emitting organic light-emitting diodes (I-TOLEDs). It can be seen that the inserting of the PbO2 EIL significantly reduces operational voltage, thus greatly improving the current efficiency and power efficiency of fabricated I-TOLEDs. The 10-(2-benzothiazolyl)-1, 1, 7, 7-tetramethyl-2, 3, 6, 7-tetrahydro-1H, 5H, 11H-[1] benzopyrano [6, 7, 8-ij] quinolizin-11-one (C545T)-based I-TOLEDs with the PbO2 EIL exhibit a maximum current efficiency of 31.6 cd A(-1) and a maximum power efficiency of 14.3 lm W-1, which are both higher than 22.5 cd A(-1) and 5.4 lm W-1 of the I-TOLEDs with LiF as the EIL respectively. A detailed analysis with respect to the role mechanism of PbO2 in electron injection has been presented. The improvement in EL performance is attributed to the formation of the interfacial dipoles at the electrode interface due to charge transfer between PbO2 and Alq(3).

Synthesis and Application of Thiadiazoloquinoxaline-Containing Chromophores as Dopants for Efficient Near-Infrared Organic Light-Emitting Diodes

series of a donor-acceptor-donor type of near-infrared (NIR) fluorescent chromophores based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) as an electron acceptor and triphenylamine as an electron donor are synthesized and characterized. By introducing pendent phenyl groups or changing the pi-conjugation length in the TQ core, we tuned tile energy levels of these chromophores, resulting in the NIR emission in a range from 784 to 868 nm. High thermal stability and glass transition temperatures allow these chromophores to be used as dopant emitters, which can be processed by vapor deposition for the fabrication of organic light-emitting diodes (OLEDs) having the multilayered structure of ITO/MoO3/NPB/Alq(3):dopant emitter/BCP/Alq(3)/LiF/Al. The electroluminescence spectra of the devices based on these new chromophores cover a range from 748 to 870 nm. With 2 wt % of dopant 1, the LED device shows an exclusive NIR emission at 752 nm with the external quantum efficiency (EQE) as high as 1.12% over a wide range of current density (e.g., around 200 mA cm(-2)).

Diarylmethylene-bridged 4,4 '-(bis(9-carbazolyl))biphenyl: morphological stable host material for highly efficient electrophosphorescence

novel compound (BCBP) based on the modification of a well-known host material 4,4'-(bis(9-carbazolyl))biphenyl (CBP) through arylmethylene bridge linkage was synthesized, and fully characterized. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied. A high glass transition temperature (T-g) of 173 degrees C is observed for BCBP due to the introduction of the bridged structure, remarkably contrasting with a low T-g of 62 degrees C for CBP. Furthermore, the bridged structure enhances the conjugation and raises the HOMO energy, thus facilitating hole-injection and leading to a low turn-on voltage in an electroluminescent device. With the device structure of ITO/MoO3/NPB/Ir complex: BCBP/BCP/Alq(3)/LiF/Al, maximum power efficiencies of 41.3 lm/W and 6.3 lm/W for green- and blue-emitting OLED were achieved, respectively.

Nonconjugated Carbazoles: A Series of Novel Host Materials for Highly Efficient Blue Electrophosphorescent OLEDs

A series of carbazole derivatives was synthesized and their electrical and photophysical properties were investigated. It is shown that the triplet energy levels of these hosts are higher than that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C-2'] picolinate (FIrpic) and the most extensively used phosphorescent host material 4,4'-N,N'-dicarbazole-biphenyl (CBP). These new host materials also showed good thermal stability and high glass transition temperatures (T-g) ranging from 78 to 115 degrees C as the linkage group between the carbazoles was altered. Photophysical measurements indicate that the energy transfer between these new hosts and FIrpic is more efficient than that between CBP and FIrpic. Devices incorporating these novel carbazole derivatives as the host material doped with FIrpic were fabricated with the configurations of ITO/NPB (40 nm)/host:FIrpic (30 nm)/BCP (15 nm)/AlQ (30 nm)/LiF (1 nm)/Al (150 nm). High efficiencies (up to 13.4 cd/A) have been obtained when 1,4-bis (4-(9H-carbazol-9-yl)phenyl)cyclohexane (CBPCH) and bis(4-(9H-carbazol-9-yl)phenyl) ether (CBPE) were used as the host, respectively.

Luminescent Boron-Contained Ladder-Type pi-Conjugated Compounds

Four diboron-contained ladder-type pi-conjugated compounds 1-4 were designed and synthesized. Their thermal, photophysical, electrochemical properties, as well as density functional theory calculations, were fully investigated. The single crystals of compounds 1 and 3 were grown, and their crystal structures were determined by X-ray diffraction analysis. Both compounds have a ladder-type g-conjugated framework. Compounds I and 2 possess high thermal stabilities, moderate solid-state fluorescence quantum yields, as well as stable redox properties, indicating that they are possible candidates for emitters and charge-transporting materials in electroluminescent (EL) devices. The double-layer device with the configuration of [ITO/NPB (40 nm)/1 or 2 (70 nm)/LiF (0.5 nm)/Al (200 nm)] exhibited good EL performance with the maximum brightness exceeding 8000 cd/m(2).

Application of Ru(bpy)(3)(2+) in control and formation of gold surface nanostructure through oxidation-reduction cycling

It was studied that the nanostructure formed on a gold surface via a simple oxidation-reduction cycles (ORC) in 0.1 M KCl containing Ru(bpy)(3)(2+) with different concentrations. Atomic force microscopy (AFM) and energy-dispersed spectroscopy (EDS) were used to characterize the nanostructure formed on the gold surface. Sweep-step voltammetry and corresponding electroluminescence (ECL) response, in situ electrochemical quartz crystal microbalance (EQCM) measurement were used to monitor the ORC. procedure. It was found that the surface structure became more uniform in the presence of Ru(bpy)(3)(2+), and the surface roughness was decreasing with the increasing of Ru(bpY)(3)(2+) concentration, suggesting a simple and effective method to control the formation of nanostructure on the gold surface.

Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices

We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA)(3)phen (x):CBP/BCP/ ALQ/LiF/Al, where x is the weight percentage of Eu(TTA)3phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Forster energy transfer participates in EL process. At the current density of 10.0 and 80.0mA/ cm(2), 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Forster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Forster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Forster energy transfer compared with carrier trapping.

Synthesis, structure, photoluminescence, and electroluminescence properties of a new dysprosium complex

A new dysprosium complex Dy(PM)(3)(TP)(2) [where PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone and TP = triphenyl phosphine oxide] was synthesized, and its single-crystal structure was also studied. Its photophysical properties were studied by absorption spectra, emission spectra, fluorescence quantum efficiency, and decay time of the f-f transition of the Dy3+ ion. In addition, the antenna effect was introduced to discuss the energy transfer mechanism between the ligand and the central Dy3+ ion. Finally, a series of devices with various structures was fabricated to investigate the electroluminescence (EL) performances of Dy(PM)(3)(TP)(2). The best device with the structure ITO/CuPc 15 nm/Dy complex 70 nm/BCP 20 nm/AlQ 30 nm/LiF 1 nm/Al 100 nm exhibits a maximum brightness of 524 cd/m(2), a current efficiency of 0.73 cd/A, and a power efficiency of 0.16 lm/W, which means that a great improvement in the performances of the device was obtained as compared to the results reported in published literature. Being identical to the PL spectrum, the EL spectrum of the complex also shows characteristic emissions of the Dy3+ ion, which consist of a yellow band at 572 nm and a blue emission band at 480 nm corresponding to the F-4(9/2)-H-6(13/2) and F-4(9/2)-H-6(15/2) transition of the Dy3+ ion, respectively. Consequently, an appropriate tuning of the blue/yellow intensity ratio can be presumed to accomplish a white luminescent emission.

Efficient organic electroluminescent devices based on an organosamarium complex

Several organic electroluminescent devices with different device structures were fabricated based on an organosamarium complex Sm(HFNH)(3)phen[HFNH=4, 4, 5, 5, 6, 6, 6-heptafluoro-l-(2-naphthvl)hexane-1, 3-dione; phen=1, 10-phenanthroline] as emitter. Their electroluminescent properties were investigated in detail. Although the devices with the optimal structure ITO/TPD (50nm)/ Sm(HFNH)(3)phen (xwt%):CBP (50nm)/BCP (20nm)/AIQ (30nm)/LiF (1 nm),/Al (200nm) show high brightness (more than 400cd/m(2)) and high current efficiency (about 1 cd/A), there are emissions from CBP, BCP and even from AIQ existing in the electroluminescence (EL) spectra besides emission from Sm(HFNH)(3)Phen. The reason to this was discussed. The device with the structure ITO/TPD (50 nm)/ Sm(HFNH)(3)phen (50 nm)/AIQ (30 nm)/LiF (1 nm)/Al (200 nm) exhibits the maximum brightness of 118 cd/m(2) and current efficiency of 0.029 cd/A, and shows emissions from AIQ and Sm(HFNH)(3)phen at high voltages. However, with the BCP hole-block layer added, the device [ITO/TPD (50 nm)/Sm(HFNH)(3)phen (50 nm)/BCP (20 nm)/AIQ (30 nm)/LiF (1 nm)/Al (200 nm)] exhibits pure Sm3+ emission in 2 the EL spectra even at high voltages, with the maximum current efficiency of 0.29cd/A and brightness of 82cd/m(2)

Improved performances of organic light-emitting diodes with metal oxide as anode buffer

We demonstrate extremely stable and highly efficient organic light-emitting diodes (OLEDs) based on molybdenum oxide (MoO3) as a buffer layer on indium tin oxide (ITO). The significant features of MoO3 as a buffer layer are that the OLEDs show low operational voltage, high electroluminescence (EL) efficiency and good stability in a wide range of MoO3 thickness. A green OLED with structure of ITO/MoO3/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidene (NPB)/NPB: tris(8-hydroxyquinoline) aluminum (Alq(3)):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)/Alq(3)/LiF/Al shows a long lifetime of over 50 000 h at 100 cd/m(2) initial luminance, and the power efficiency reaches 15 lm/W. The turn-on voltage is 2.4 V, and the operational voltage at 1000 cd/m(2) luminance is only 6.9 V. The significant enhancement of the EL performance is attributed to the improvement of hole injection and interface stability at anode.

High efficiency tandem organic light-emitting devices with Al/WO3/Au interconnecting layer

An interconnecting layer of Al (2 nm)/WO3 (3 nm)/Au (16 nm) was studied for application in tandem organic light-emitting devices. It can be seen that the Al/WO3/Au structure plays the role of an excellent interconnecting layer. The introduction of WO3 in the connection unit significantly improves the device efficiency as compared to the case of Al/Au. Thus, the current efficiency of the two-unit tandem devices is enhanced by two factors with respect to the one-unit devices. The green two-unit tandem device of indium tin oxide/MoO3/4,4(')-N,N-'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl(NPB)/tris(8-hydroxylquinoline) aluminum (Alq(3)):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one (C545T)/Alq(3)/LiF/Al/WO3/Au/MoO3/NPB/Alq(3):C545T/Alq(3)/LiF/Al showed a maximum current efficiency of 33.9 cd/A and a power efficiency of 12.0 lm/W.

Improved electron injection in organic light-emitting devices with a lithium acetylacetonate [Li(acac)]/aluminium bilayer cathode

Lithium acetylacetonate [Li(acac)] covered with aluminium was used as an efficient electron injection layer in organic light-emitting devices (OLEDs) consisting of NPB as the hole transport layer and Alq(3) as the electron transport and light emitting layer, resulting in lower turn- on voltage and increased current efficiency. The turn- on voltage (the voltage at a luminance of 1 cd m(-2)) was decreased from 5.5 V for the LiF/Al and 4.4 V for Ca/Al to 4.0 V for Li(acac)/Al, and the device current efficiency was enhanced from 4.71 and 5.2 to 7.0 cd A(-1). The performance tolerance to the layer thickness of Li(acac) is also better than that of the device with LiF. LiF can only be used when deposited as an ultra- thin layer because of its highly insulating nature, while the Li(acac) can be as thick as 5 nm without significantly affecting the EL performance. We suppose that the free lithium released from Li(acac) improves the electron injection when Li(acac) is covered with an Al cathode.