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Experimental Demonstrations of SOLNETs
Published in Tetsuzo Yoshimura, Self-Organized Lightwave Networks, 2018
The second demonstration is shown in Figure 6.24 [13]. The experimental setup and materials are the same as those in the first demonstration. When a 405-nm write beam is introduced from the left-hand-side 50-μm optical fiber, initially, the write beam diffusely propagates in the PRI material. The Alq3/PVA target excited by the write beam emits blue/green luminescence. Then, the refractive index in the region, where the write beam and luminescence overlap, increases rapidly compared to the surrounding region. As a result, the write beam is guided toward the target as shown in Figure 6.24a, and an R-SOLNET that connects the fiber core and the luminescent target is formed as shown in Figure 6.24b. It is found that the R-SOLNET gradually expands from the fiber core diameter to the width of the Alq3/PVA target, constructing a tapered R-SOLNET. This indicates that the R-SOLNET with luminescent targets acts as optical solder with a function of a mode size converter.
Transparent and Flexible Carbon Nanotube Electrodes for Organic Light-Emitting Diodes
Published in James E. Morris, Kris Iniewski, Graphene, Carbon Nanotubes, and Nanostructures, 2017
Yu-Mo Chien, Ricardo Izquierdo
The device structure of the SWCNT OLED is shown in Figure 4.11a. An ultra-thin (~1 nm) buffer layer of parylene was also deposited by CVD between the CNTs and the stacked OLED layers, which was absent in the control ITO OLEDs present. The addition of this layer claims to improve the wetting and adhesion of the evaporated organic semiconductor layer to the CNTs. The organic semiconductor layers that formed the OLED consisted of a 10 nm copper phthalocyanine (CuPc) hole injection layer (HIL), a 50 nm N,N-bis-1-naphthyl-N,N-diphenyl-1,1-biphenyl-4,4-diamine (NPB) hole transport layer (HTL), and a 50 nm tris-8-hydroxyquinoline aluminum (Alq3) electron transport layer (ETL) and emissive layer (EL) deposited in a thermal evaporator. The surface roughness of the CNT film was measured using atomic force microscopy (AFM) at 12 nm rms. The considerable roughness of the SWCNT films imposes a lower limit to the thickness of the organic layers. Therefore 100 nm layers of NPB and Alq3 were used instead for SWCNT OLEDs. The cathode in both ITO OLED and SWCNT OLED was made by evaporating 1 nm of lithium fluoride and 50 nm of aluminum. Worth noting, Figure 4.11b shows a scanning electron microscope (SEM) image of the cross section of the SWCNT OLED. The sample for the SEM image was prepared by cleaving the glass substrate at the center Transparent and Flexible Carbon Nanotube Electrodes of the emissive area. It can be seen that the SWCNT film network is overhanging across the glass substrate where the break was made, thus illustrating the flexibility and fabric quality of the SWCNT thin film.
Molecular Designing of Luminescent Europium-Metal Complexes for OLEDs: An Overview
Published in Sanjay J. Dhoble, B. Deva Prasad Raju, Vijay Singh, Phosphors Synthesis and Applications, 2018
Sano et al. [122] also studied the EL properties of AB. The synthesized AB has an emitting layer with red emission in the El OLEDs. The organic layer is vacuum-deposited, and the device structure is glass substrate/ITO/TPD/AB/Mg:In. The Eu complex’s PL wavelength is 614 nm. This device’s PL originates in the transition between energy levels of the Eu(III) ion and does not show emission effectively because of lower EL efficiency. The observed luminescence is poor at 100 cd/m2. Adachi et al. [123] reported the energy transfer process in the device. The host material (CBP) was doped with a Eu complex (AB) in different concentrations. The device structure is ITO/TPD (50 nm)/CBP:AB (1%) (20 nm)/BCP (10 nm)/Alq3 (30 nm)/Mg:Ag (10:1, 100 nm) and achieves a maximum external EL quantum efficiency (n) of 1-4% at a current density of 0.4 mA/cm2 and a maximum luminescence of 505 cd/m2 at 12 V and 100 mAcm- 2. A significant decrease of QE was observed with increasing current along with increase in the CBP host emission due to triplet-triplet annihilation on CBP molecules following back transfer from TTA because of near resonance of the TTA and CBP triplet state. From this, the conclusion was made that the direct trapping of electrons and holes and the subsequent formation of the excitons occur on the dopant, leading to high QE at low current densities. It was further analyzed by Ohmoria et al. [124] by fabricating a single-layer-based ITO/AB:PVK/Mg:In device. The emission peak was perceived from the Eu compound and PVK at 610 nm and 420 nm, respectively. The ratio of emission peak intensity decreases with increasing Eu concentration, and at >0.01 mol% of concentration, red emission was observed. From the energy band diagram, the excitons formed are transferred successfully to the Eu complex from the PVK host.
DFT-based study of the impact of transition metal coordination on the charge transport and nonlinear optical (NLO) properties of 2-{[5-(4-nitrophenyl)-1,3,4-thiadiazol-2-ylimino]methyl}phenol
Published in Molecular Physics, 2019
Christelle Herliette Atchialefack Alongamo, Nyiang Kennet Nkungli, Julius Numbonui Ghogomu
An OLED is a device component which emits light when an external voltage is applied. It is made up of an emissive layer (EL) comprised of a film of organic compounds, a hole-transport layer (HTL) and an electron-transport layer (ETL), all of which are situated between two electrodes [4]. For the HTL materials, properties such as efficient hole injection and high hole mobility are necessary for effective delivery of charge carriers towards the emissive or active layer [3,5]. Other important properties of an HTL material are: an appropriate HOMO energy level (5.4 eV) to ensure a low potential barrier for hole injection from the anode into the EL, and a suitable LUMO energy level to block electron injection from the EL to the HTL [3]. One of the most commonly used hole-transport materials is N,N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD) [5]. For a substantially enhanced OLED performance, the ETL material should possess the following qualities: suitable Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels to allow minimisation of the potential barrier for electron injection, low turn-on/operating voltage and effective hole blocking ability [3]. On the other hand, tris(8-hydroxyquinolinato)aluminium (Alq3) is the commonest material that is used for the electron-transport layer [5].