Papers by Keyword: Light Emitting Devices

Abstract: Quantum dots of CdSe, CdS and ZnS QDs were prepared by chemical reaction and used to fabricate organic quantum dot hybrid junction device. QD-LEDs were fabricated using layers of ITO/TPD: PMMA/CdSe/Alq₃, ITO/TPD: PMMA/CdS/Alq₃ and ITO/TPD: PMMA/ZnS/Alq₃ devices which prepared by phase segregation method. The hybrid white light emitting devices consists, of three-layers deposited successively on the ITO glass substrate; the first layer was of N, N’-bis (3-methylphenyl)-N, N’-bis (phenyl) benzidine (TPD) polymer mixed with polymethyl methacrylate (PMMA) polymers. The second layer was QDs while the third layer was tris (8-hydroxyquinoline) aluminium (Alq₃). The results of the optical properties show that the prepared QDs were nanocrystalline with defects formation. The calculated of energy gaps from photoluminescence (PL) spectrometer were 2.38, 2.69 and 3.64 eV for CdSe, CdS and ZnS respectively. The generated white light has acceptable efficiency using confinement effect which makes the energy gap larger, so that the direction of the light sites are toward the center of white light color. The hybrid junction devices (EL devices) were characterized by room temperature PL and electroluminescence (EL). Current-voltage (I–V) characteristics indicate that the output current is good compared to the few voltages ( 8-10.3 V) used which gives acceptable results to get a generation of white light. The EL spectrum reveals a broad emission band covering the range from 350 - 700 nm. The emissions causing this white luminescence were identified depending on the chromaticity coordinates (CIE 1931). The correlated color temperature (CCT) was found to be about 6250, 5310 and 5227K respectively. Fabrication of EL-devices from semiconductors material (CdSe, CdS and ZnS QDs) with hole injection organic polymer (TPD) and electron injection from organic molecules (Alq₃) was effective in white light generation

Abstract: Heterocyclic electron-poor monomer [1,2,5]thiadiazolo[3,4-c]pyridine have been synthesized in high yields over five steps from readily available starting materials. The new deficient acceptor has good solubility in organic solvents so as to permit an appropriate coating process.

Abstract: Heterocyclic monomers based on 2,1,3-benzothiadiazole bearing solubilizing side chains have been synthesized in high yields over four steps from readily available starting materials. A multistep synthesis of the electron-poor 6, 7-dihydro-1, 4-dioxino-[2, 3-f][2,1,3]-benzothiadiazole are presented. The new dificient acceptor has good solubility in organic aolvents to permit an appropriate coating process.

Abstract: Single crystal Si, Si0.948Ge0.052 and Si0.66Ge0.34 diode as well as Ge transistor structures with high electroluminescence (EL) intensities in the region of interband transitions at room temperature were fabricated by different techniques and their luminescence properties were studies. The analysis of the experimental data shows that recombination involving excitons is the dominant mechanism of near-band edge radiative recombination in all the light-emitting structures at room temperature. Some of the structures are characterized by record values of EL intensity and/or external quantum efficiency, so they can be used as effective light emitters for Si optoelectronics.

Abstract: Structural defects in Si:Er layers grown by molecular beam epitaxy have been studied by transmission electron microscopy. Two kinds of second phase precipitates are the main defects in the layers with Er concentration ≥ 2х1019 cm-3: ball-shaped precipitates (4-25 nm) of metallic Er localized at the layer-substrate interface and platelet precipitates of ErSi2 extending through the whole layer. We studied the effect of Er concentration (8х1018 - 4х1019 cm-3) and growth temperature (400 - 700°C) on the defect generation. The peculiarities of defect generation in MBE Si:Er layers implanted with B+ ions were also studied.