Hyoung-Yun Oh

Highly Efficient Red Phosphorescent Dopants in Organic Light‐Emitting Devices

Phosphorescent organic light-emitting diodes (PHOLEDs) have been developed for more than 10 years. As a result, the highly effi cient red PHOLED materials are now utilizing in commercial active-matrix organic light-emitting diodes (AMOLEDs) and lighting. Nevertheless, the development of much more effi cient PHOLEDs is still required due to a dramatic reduction of power consumption by LED backlight in thin fi lm transistor-liquid crystal display (TFT-LCDs) and the generation of new lighting applications with comparable effi ciency of fl uorescent lamps. There have been many studies about improving the effi ciency of red PHOLEDs by developing host and dopant materials. However, the radiative and nonradiative rate constants ( k r , k nr ) have a strong dependence on the energy gap ( Δ E ) between the emissive excited state and the ground state in accordance with “the energy gap law”, which indicates that k nr increases with a decrease in Δ E . Hence it is obvious that highly effi cient red emission with smaller Δ E tends to give larger k nr and smaller k r , leading to the lower emission quantum yield. [ 1 , 2 ]

The pattern of bone marrow oedema on MRI in osteonecrosis of the femoral head

It has been suggested that transient osteoporosis or the bone marrow oedema syndrome (BMOS) may be the initial phase of osteonecrosis of the femoral head (ONFH) and that there may be a common pathophysiology. In this study, we have assessed the MR images of 200 consecutive patients with ONFH in respect of the BMO pattern in order to test this hypothesis. This pattern was not observed in the early stage of ONFH. The initial abnormal finding detected on the MR images was an abnormal band of intensity at the junction between the necrotic area and the normal bone. Structural damage of the head seems to result in the appearance of the BMO pattern and the development of pain in ONFH. There was no finding to support the existence of a continuum between BMOS and ONFH.

Small single–triplet energy gap bipolar host materials for phosphorescent blue and white organic light emitting diodes

We report extremely high efficiency tandem white organic light-emitting diodes (OLEDs) with newly synthesized host materials. Our new host materials have well balanced bipolar characteristics and very small singlet to triplet splitting energies (∼0.4 eV) due to almost no orbital overlapping between ground and excited states. The fabricated blue phosphorescent device with one of these host materials shows very high external quantum efficiency of 25.7%, low onset and driving voltages of 2.47 V and 3.49 V at 1 and 1000 cd m−2, respectively. High performance asymmetric tandem OLEDs could be fabricated by adopting these efficient and low driving voltage blue unit and very efficient yellow unit devices. Power efficiency of 63.1 lm W−1 and current efficiency of 128.8 cd A−1 at 1000 cd m−2 were achieved without any light out-coupling technology. We expect that blue phosphorescent OLEDs with our new narrow band-gap bipolar host materials could be a promising solution to make high efficiency white OLEDs for display and lighting applications.

Effective Electrophosphorescence Emitting Devices by Using New Type Ir(III) Complex with Bluky Substistuent Spacers

The new green Ir(III) complex, fac-tris[4-methyl-2-(4′-trimethylsilylph-enyl)pyridine] [Ir(msippy)3], is synthesized and phosphorescent light emitting devices fabricated by using them as triplet emissive dopants. Ir(dsippy)3 in UV-Vis. spectra showed absorption band at 395 nm originating from 1MLCT. The EL devices with configuration of ITO/CuPc (10 nm)/α -NPD (40 nm)/CBP-Ir(msippy)3 (20 nm)/BCP (10 nm)/Alq3 (40 nm)/LiF (1 nm)/Al (100 nm).showed the emission maximum at 516 nm, due to the radiative decay from 3MLCT state to ground state. The 6% doped devices showed the maximum efficiency of 49.9 cd/A and power efficiency 25.3 lm/W. The observed PL quantum efficiency (0.43) of the [Ir(msippy)3] in CH2Cl2 shows slightly higher than that of reported Ir(ppy)3 (Φ = 0.40).

P-140: High Efficient Anthracene-Based Blue Light Emitting Material for OLED

The novel blue light emitting materials, 9,10-Bis(9′,9′-diethyl-7′-diphenylamino-fluoren-2-yl)-anthracene, which is composed of an anthracene as main unit and a rigid, bulky, easy hole transportable and energy transferable phenylamine substituted fluorene containing as side unit, was designed and synthesized. The theoretical calculation of 3 dimensional structure and the energy densities of HOMO and LUMO states, as well as optical properties of new obtained material, support that it has a non coplanar structure and that intramolecular energy transfer occurs from the side units to the main unit, resulting in high luminescent efficiency and high color purity. With the newly designed blue emitting material in the multilayer device structure, it was possible to achieve the luminous efficiency of 4.2 cd/A (3.3 % of quantum efficiency at 7.5V). The EL spectrum of the multilayer device showed a narrow emission band with full width at half maximum (fwhm) 53 nm and a λmax = 461 nm.

Synthesis and Electrochemical Evaluation of Li, Mn-Rich Cathode Materials for Advanced Lithium Batteries.

Li2MnO3-based composite, xLi2MnO3-(1--x)LiMO2 (M = Ni, Co, Mn, etc.), was synthesized via co-precipitation with sintering treatment. The composite material has hexagonal structure including a little of monoclinic with a nano-crystallite size. As a result, the material showed a specific redox behavior in the voltage range of 2.0-4.6 V and approximately 267 mAh/g of discharge capacity was obtained at the room temperature.