Language：English   Publishing type：Research paper (scientific journal)  

Enhanced electroluminescence efficiency is achieved in organic light-emitting diodes through delayed fluorescence of the exciplex state formed between 4,40,4 ''-tris[3-methylphenyl(phenyl) amino]triphenylamine (m-MTDATA) as an electron-donating material and 2,8-bis(diphenylphosphoryl) dibenzo[b,d]thiophene (PPT) as an electron-accepting material. The devices exhibited maximum external electroluminescence quantum and power efficiencies of 10.0% and 47.0 lm/W, respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737006]

DOI： 10.1063/1.4737006

Language：English   Publishing type：Research paper (scientific journal)  

Light emission from organic light-emitting diodes that make use of fluorescent materials have an internal quantum efficiency that is typically limited to no more than 25% due to the creation of non-radiative triplet excited states. Here, we report the use of electron-donating and electron-accepting molecules that allow a very high reverse intersystem crossing of 86.5% between non-radiative triplet and radiative singlet excited states and thus a means of achieving enhanced electroluminescence. Organic light-emitting diodes made using m-MTDATA as the donor material and 3TPYMB as the acceptor material demonstrate that external quantum efficiencies as high as 5.4% can be achieved, and we believe that the approach will offer even higher values in the future as a result of careful material selection.

DOI： 10.1038/nphoton.2012.31

Language：English   Publishing type：Research paper (scientific journal)  

We present new information that requires explanation in the study of possible mechanisms for fluorescence blinking in single nanocrystal (NC) quantum dots. By using pulse laser excitation, we investigated the excitation intensity dependence of fluorescence blinking statistics in NC quantum dots embedded in polymer matrices. Under strong excitation intensity, we observed an unexpected excitation intensity dependence of the power-law distribution in the blinking statistics. To explain the new information on the blinking statistics in the framework of the Tang-Marcus model, we propose a diffusion-controlled model based upon anharmonic potentials that originate from a nonlinear response of polarization to the electric field and is caused by an increase in the dielectric constant of host media with the excitation intensity. The validity of the proposed model is investigated by comparing the blinking statistics for two host matrices.

DOI： 10.1021/jp811448k

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.1862777

Publishing type：Research paper (scientific journal)   Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers  

Luminescent lanthanide ions incorporated in sodium yttrium fluoride nanocrystals are promising as new luminescent materials in optoelectronics and bioimaging since the nonradiative transition is significantly suppressed due to the absence of high-energy vibrational modes. To prepare optically and electrically active nanocrystals, we explored organic ligands that allow efficient triplet energy transfer to Eu3+ incorporated into nanocrystals, resulting in an efficient photosensitization effect in colloidal solutions and films. Further, we applied these emitting nanocrystals to light-emitting devices and observed the electroluminescence.

DOI： 10.35848/1347-4065/ad760d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Advanced Materials  

Hexacarbazolylbenzene (6CzPh), which is benzene substituted by six carbazole rings, is a simple and attractive compound. Despite the success of a wide variety of carbazole derivatives in organic light-emitting diodes (OLEDs), 6CzPh has not received attention so far. Here, we reveal excellent performances of 6CzPh as a host material in OLEDs regarding conventional host materials. Various strategies have been implemented to improve the performance of OLEDs, e.g., triplet utilization by thermally activated delayed fluorescence (TADF) and phosphorescence emitters for maximizing internal quantum efficiency, and molecular orientation control for increasing outcoupling efficiency. The present host material is suited for both criteria. Robustness of the structure and sufficiently high triplet energy enables a high external quantum efficiency with a long device lifetime. Besides, the host material boosts the horizontal molecular orientations of several guest emitters. It is noteworthy that disk-shaped 4CzIPN marks the complete horizontal molecular orientations (Θh = 100%, S = -0.50). These results provide an effective way of improving efficiencies without sacrificing device durability for future OLEDs. This article is protected by copyright. All rights reserved.

DOI： 10.1002/adma.202402275

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Publishing type：Research paper (scientific journal)   Publisher：Advanced Functional Materials  

Recent advances in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF)-assisted fluorescence (TAF) attest to the great promise of this technology in practical use. However, the simultaneous realization of high efficiency and device durability in blue OLEDs remains a significant challenge. Clarification of the degradation mechanisms correlated to molecular structure and device configuration is the key to extending the device lifetime. In this study, electron transport materials incorporating two triazine units in close proximity are adopted to use in hole-blocking and electron-transporting layers, resulting in superior device performances. In addition, a modified photodegradation experiment reveals that the degradation origins closely relate to charge carriers. The optimization of the device according to the obtained findings leads to 4.5 times extension in the lifetime of the TAF-OLED using a multiple resonance emitter. These results also provide guidelines for designing robust electron transport materials for blue OLEDs.

DOI： 10.1002/adfm.202402287

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Language：Others   Publishing type：Research paper (scientific journal)  

Abstract

It is well known that triplet–triplet annihilation upconversion (TTU) can enhance electroluminescence (EL) efficiency by converting two low‐energy triplet excitons into one high‐energy singlet exciton. However, conventional intermolecular TTU requires high doping concentration to activate, limiting device architecture. Here, six dimer molecules comprised of two anthracene units connected by a spacer unit are investigated, which have a possibility of the intramolecular TTU process. As a result, two dimer molecules show high TTU efficiencies close to the theoretical maximum even in dispersed, diluted conditions. By comparing these molecular conformations, a correlation is found between the dimer structures of two anthracene units and the TTU activity in the diluted condition, i.e., the 3D molecular structure with the exciton utilizing efficiency.

DOI： 10.1002/adom.202301924

Language：Others   Publishing type：Research paper (scientific journal)  

Abstract

A considerable variety of donor–acceptor (D–A) combinations offers the potential for realizing highly efficient thermally activated delayed fluorescence (TADF) materials. Multiple D–A type compounds are one of the promising families of TADF materials in terms of stability as well as efficiencies. However, those emitters are always composed of carbazole-based donors despite a wide choice of moieties used in linearly linked single D–A molecules. Herein, we developed a multiple D–A type TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design. The new emitter exhibits high photoluminescence quantum yield (PLQY) in various conditions including polar media blend and high concentrations. Organic light-emitting diodes (OLEDs) showed a reasonably high external quantum efficiency (EQE). In addition, we revealed that the multiple-D–A type molecules showed better photostability than the single D–A type molecules, while the operational stability in OLEDs involves dominant other factors.

DOI： 10.1038/s41598-023-34623-9

Language：Others   Publishing type：Research paper (scientific journal)  

Highly efficient light harvesting of a Eu(iii) complex in a host–guest film by triplet sensitization
Very high photoluminescence intensity of a Eu(iii) complex is achieved using a host–guest system. The intensity is 400 times larger than that of the Eu(iii) complex itself.

DOI： 10.1039/D3SC01817B

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adma.202211160

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.202202734

Language：English   Publishing type：Research paper (scientific journal)  

Multi-resonance emitters (MREs) are a promising candidate for fulfilling the harsh requirements of display applications due to their unique photophysical properties. Recently, MREs have been widely used as a terminal emitter in hyperfluorescence organic light-emitting diodes (HF-OLEDs); however, since MREs are always thermally activated delayed fluorescence (TADF)-active, possessing long triplet lifetimes in millisecond order, they result in severe chemical degradation. Instead of shortening the delayed lifetime of MREs by molecular design, herein, a low-triplet pyrene unit is introduced into an MRE scaffold to achieve narrowband emission and quick removal of triplets in MREs simultaneously. Blue HF-OLED based on the non-TADF MRE demonstrates a high external quantum efficiency of 20% and a tenfold improvement in stability, compared to those of the HF-OLEDs with standard MREs. An opposite direction of molecular design of MREs for the sophisticated exciton generation and transfer system in HF-OLEDs is proposed to enhance device lifetime without sacrificing color purity and efficiency.

DOI： 10.1002/adom.202200682

Language：English   Publishing type：Research paper (scientific journal)  

There is increasing interest in thermally activated delayed fluorescence (TADF) in materials, and to understand its mechanism in the excited state dynamics. Recent challenges include color purity, efficient deep-blue emission, fast exciton decay lifetimes, high reverse intersystem crossing rates (k(RISC)), low-efficiency roll-off in organic light-emitting diodes (OLEDs), and long device lifetimes. Here, a series of compounds having benzonitrile and carbazole rings are examined, that provide a detailed understanding of the excited states, and a guideline for high-performance TADF. A dense alignment of the excited states with several different characters within a small energy range results in high k(RISC) of >2 x 10(6) s(-1), while maintaining radiative rate constants (k(r)) >10(7) s(-1). OLEDs based on the optimum compound exhibit a low-efficiency roll-off and a CIEy (y color coordinate of Commission Internationale de l'eclairage) <0.4. TADF-assisted fluorescence (TAF) OLED exhibits a maximum external quantum efficiency of 22.4&#37; with CIE coordinates (0.13,0.15). This work also provides insights for device engineering and molecular designs.

DOI： 10.1002/adfm.202204352

Language：English   Publishing type：Research paper (scientific journal)  

This work reports a new acceptor for constructing donor-acceptor type (D-A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D-A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85&#37; in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D-A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5&#37;.

DOI： 10.1039/d2sc02478k

Language：Others   Publishing type：Research paper (scientific journal)  

The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.

DOI： 10.1021/acs.jpclett.1c03983

Language：English   Publishing type：Research paper (scientific journal)  

Achieving continuous-wave (CW) lasing in organic semiconductors is known to be a difficult task because long-lived triplets quench radiative singlets via singlet-triplet annihilation (STA). To avoid STA and operate organic lasers in CW or long-pulse photoexcitation, the triplets need to be removed from an organic laser gain medium. However, this triplet removal leads to a loss of excitons. In addition to removing the detrimental triplets, here it is reported a triplet recycling process, which includes triplet scavenging and successive triplet upconversion via triplet-triplet annihilation (TTA) to regenerate emissive singlet excitons in a laser medium. An anthracene derivative of 9-(1-naphthalenyl)-10-(4-(2-naphthalenyl)phenyl)anthracene (NaNaP-A) and a laser dye of 4,4 '-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi) are used as the triplet recycling sensitizer and the emitting laser dye, respectively. In this laser system, NaNaP-A can efficiently scavenge the triplets formed on BDAVBi because the triplet level is deeper for NaNaP-A than for BDAVBi, and then NaNaP-A successively recycles the triplets into the BDAVBi's singlet state via TTA. The TTA compensates and overcomes the STA in this laser system. Hence, these laser devices can be operated with long pulse widths of up to 10 ms. This unique triplet recycling behavior is confirmed by transient photoluminescence (PL) and electroluminescence (EL) studies.

DOI： 10.1002/adom.202101302

Language：English   Publishing type：Research paper (scientific journal)  

Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called "hot exciplexes" that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T-1 to T-2 spacing. The hot exciplex model is investigated using optical spectroscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T-3 to the S-1 state within only a few nanoseconds. Application and practicality of the model are shown by fabrication of organic light-emitting diodes with up to 32 &#37; hot exciplex contribution and low efficiency roll-off.Molecular designs improving the performance of thermally activated delayed fluorescence (TADF) emitters are greatly desired for optoelectronic applications. The authors propose a molecular geometry with donor and acceptor moieties facing each other separated by an anthracene bridge, giving rise to hot exciplex states producing color pure and fast TADF emission.

DOI： 10.1038/s41467-021-26439-w

Language：English   Publishing type：Research paper (scientific journal)  

Continuous-wave (CW) lasing is still difficult to realize in organic laser dyes, one reason being the thermal degradation caused by intense photoexcitation. A decrease in laser threshold suppresses the thermal degradation and, therefore, leads to long-lasting lasing from organic laser dyes. Here, we show that it is possible to decrease the laser thresholds by combining the organic laser dye 4,4-bis[(N-carbazole)styryl]biphenyl, which has a small spectral overlap between the laser emission and the excited-state triplet absorption, with two-dimensional (2D) distributed-feedback (DFB) gratings. We used second-order 2D cross double and square lattice DFB gratings, which offer light feedback in two orthogonal directions, and second-order and mixed-order circular DFB gratings, which offer light feedback in radial directions. Among these grating structures, the mixed-order circular DFB grating structure led to the lowest lasing threshold of similar to 0.015 mu J cm(-2) under short-pulse photoexcitation because of the excellent optical feedback. Moreover, a low average-power threshold of 10 W cm(-2) (a peak-power threshold of 1 kW cm-2) was obtained when laser devices with this grating structure were operated under 1 s of long-pulse photoexcitation with a repetition rate of 0.01 Hz. Additionally, using the mixed-order circular DFB grating structure improved the laser stability under CW photoexcitation since shorter exciton lifetimes in the optical resonator suppress the chemical decomposition. These results demonstrate the importance of choosing an optical resonator structure for improving organic laser performance.

DOI： 10.1021/acsphotonics.0c01728

Language：English   Publishing type：Research paper (scientific journal)  

A tetracene dimer, 5,5'-bitetracene (55BT), has successfully been synthesized for the first time and its structure was confirmed by X-ray single crystal analysis. The electrochemical and optical properties of 55BT were investigated and compared to those of tetracene. Although the photoluminescence quantum yield of 55BT was slightly higher than that of tetracene, the results of the transient absorption spectroscopy suggested triplet formation by singlet fission in solution.

DOI： 10.1246/cl.200909

Language：English   Publishing type：Research paper (scientific journal)  

The development of near-infrared (NIR) light sources has attracted much interest due to their attractive applications, such as biosensing and light detection and ranging (LiDAR). In particular, organic semiconductor laser diodes with NIR emission are emerging as a next generation technology. However, organic NIR emitters have generally suffered from a low quantum yield, which has resulted in only a few examples of organic solid-state NIR lasers. In this study, the authors demonstrate a highly efficient NIR emitter based on a boron difluoride curcuminoid structure, which shows a high photoluminescence (PL) quantum yield (phi(PL)) at >700 nm and a high fluorescence radiative rate constant in a solid-state film. Amplified spontaneous emission and lasing occurs at >800 nm with very low thresholds. The large redshift of the stimulated emission is attributed to the transition from the lowest excited state to the different vibrational levels of the ground state owing to the overlap between the emission and the singlet-singlet excited-state absorption.

DOI： 10.1002/adom.202001947

Language：English   Publishing type：Research paper (scientific journal)  

Large external quantum efficiency rolloff at high current densities in organic light-emitting diodes (OLEDs) is frequently caused by the quenching of radiative singlet excitons by long-lived triplet excitons [singlet-triplet annihilation (STA)]. In this study, we adopted a triplet scavenging strategy to overcome the aforementioned STA issue. To construct a model system for the triplet scavenging, we selected 2,6-dicyano-1,1-diphenyl-lambda (5)sigma (4)-phosphinine (DCNP) as the emitter and 4,4-bis[(N-carbazole)styryl]biphenyl (BSBCz) as the host material by considering their singlet and triplet energy levels. In this system, the DCNP's triplets are effectively scavenged by BSBCz while the DCNP's singlets are intact, resulting in the suppressed STA under electrical excitation. Therefore, OLEDs with a 1wt.&#37;-DCNP-doped BSBCz emitting layer demonstrated the greatly suppressed efficiency rolloff even at higher current densities. This finding favourably provides the advanced light-emitting performance for OLEDs and organic semiconductor laser diodes from the aspect of the suppressed efficiency rolloff. Though organic light-emitting diodes are highly desirable for display and lighting applications, efficiency roll-off at high current densities limits its applicability. Here, the authors report a triplet scavenging strategy for improved triplet exciton management and reduced efficiency roll-off.

DOI： 10.1038/s41467-020-18292-0

Language：English   Publishing type：Research paper (scientific journal)  

Quenching of singlets by long-lived triplets is a serious issue for lasing from organic laser dyes, especially under long pulse excitation. As a strategy to scavenge or manage unnecessary triplets, an organic laser dye is dispersed into a host material having high singlet and low triplet energy levels [a large singlet-triplet energy gap (Delta E-ST)]. However, finding such a host material having a triplet scavenging capability is limited. In this study, an organic laser dye, 2,6-dicyano-1,1-diphenyl-lambda(5)sigma(4)-phosphinine (DCNP), having a small Delta E-ST of approximate to 0.44 eV is synthesized, and thus 4-4 '-bis[(N-carbazole)styryl] biphenyl (BSBCz) can be employed as a triplet scavenging host, i.e., the triplets formed on DCNP are easily transferred to BSBCz. A 1 wt&#37;-DCNP-doped BSBCz film is formed on a mixed-order distributed feedback grating, showing lasing with a low threshold value of approximate to 0.86 mu J cm(-2) and a full-width-at-half-maximum value of approximate to 0.5 nm. Because of the suppressed singlet-triplet annihilation, DCNP-based laser devices operating under a continuous-wave regime, with a low threshold of 72 W cm(-2) and a long laser half-lifetime of approximate to 3 min, are demonstrated. These results indicate a possibility of the wider selection of host materials, easing a material design strategy of fabricating high-performance laser devices in future.

DOI： 10.1002/adfm.202001078

Language：English   Publishing type：Research paper (scientific journal)  

For a better understanding of the exciton decay process in thermally activated delayed fluorescence (TADF) emitters, the intersystem crossing rate, k(ISC), is one of the important physical constants that have to be determined. Herein, a method to calculate the k(ISC) value from photoluminescence (PL) measurements is reconsidered. The k(ISC) value can be determined at very low temperatures where delayed fluorescence (DF) is completely suppressed, as well as around room temperature where triplet excitons mainly decay into the ground state by emitting DF. However, there is a temperature range where the k(ISC) value cannot be determined accurately because the influences of nonradiative decay paths can be neither ignored nor corrected. For such a temperature range, an alternative approach, which utilizes the temperature dependence of an observed PL decay rate, is presented. In this way, k(ISC) values from 300 to 10 K are determined for thin films of two TADF emitters, i.e., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene, which are known as 4CzIPN and 2CzPN, respectively.

DOI： 10.1002/pssa.201900616

Language：English   Publishing type：Research paper (scientific journal)  

Excited states of emissive organic molecules undergo various kinds of quenching phenomena such as vibration-coupled quenching depending on their environmental conditions. Because bright singlet excitons in purely organic molecules exhibiting thermally activated delayed fluorescence (TADF) can access dark triplet excited states, photogenerated singlet excitons can decay nonradiatively through both singlet and triplet excited states. Here, we investigated nonradiative decay behavior, including internal and external exciton quenching processes, of various types of TADF materials in solution. Under air-saturated conditions, both the lowest singlet and triplet excited states of almost all of the TADF materials showed oxygen quenching. We considered the effect of oxygen quenching for both spin states to develop a method for determination of the triplet contribution to the total photoluminescence quantum yield from the transient photoluminescence profiles. Furthermore, we observed a clear energy gap law for the internal nonradiative processes.

DOI： 10.1021/acs.jpclett.9b03302

Language：English   Publishing type：Research paper (scientific journal)  

For a better understanding of the exciton decay process in thermally activated delayed fluorescence (TADF) emitters, the intersystem crossing rate, k_ISC, is one of the important physical constants that have to be determined. Herein, a method to calculate the k_ISC value from photoluminescence (PL) measurements is reconsidered. The k_ISC value can be determined at very low temperatures where delayed fluorescence (DF) is completely suppressed, as well as around room temperature where triplet excitons mainly decay into the ground state by emitting DF. However, there is a temperature range where the k_ISC value cannot be determined accurately because the influences of nonradiative decay paths can be neither ignored nor corrected. For such a temperature range, an alternative approach, which utilizes the temperature dependence of an observed PL decay rate, is presented. In this way, k_ISC values from 300 to 10 K are determined for thin films of two TADF emitters, i.e., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene, which are known as 4CzIPN and 2CzPN, respectively.

DOI： 10.1002/pssa.201900616

Language：Japanese  

Time-resolved photoluminescence spectra of 2CzPN with sky blue emission

DOI： 10.11470/jsapmeeting.2019.2.0_2621

Language：English   Publishing type：Research paper (scientific journal)  

This work investigates the feasibility of using low-dimensional perovskites for electrically driven lasers given the current status of perovskite light-emitting diodes and optically pumped lasers. In our progress toward electrically driven lasers, we performed a variety of measurements on bulk and low-dimensional perovskite films to give a baseline for expectations. This included the measurement of amplified spontaneous emission, lasing, and near-infrared light-emitting diodes operated at low and high current density. We considered power density thresholds needed for amplified spontaneous emission and lasing and compared this to light-emitting diodes operated at high current density to speculate on the future of electrically driven perovskite lasers. We concluded that our current perovskite devices will need current densities of similar to 4 to 10 kA/cm(2) to achieve lasing. Future devices will most significantly benefit from architectures that accommodate higher current, but meaningful reductions in threshold may also come from improved film quality and confinement.

DOI： 10.1021/acsphotonics.8b01413

Language：English   Publishing type：Research paper (scientific journal)  

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.

DOI： 10.1002/adma.201802662

Language：English   Publishing type：Research paper (scientific journal)  

Triplet-triplet annihilation (TTA) will change the ratio between fluorescence and phosphorescence in the photoluminescence spectrum of a thermally activated delayed fluorescence emitter at very low temperature. Using the resultant spectral blueshift, this study investigated the nature of TTA in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) doped in a host material. The spectral blueshift is not caused by singlet-triplet annihilation and the emitter saturation effect and is less influenced by the emitter aggregates, particularly for the case of a lower doping concentration. Using these features, it is possible to focus on TTA. For 4CzIPN, the spectral blueshift due to TTA is recognized even in samples with the doping concentration as low as 1 wt. &#37;. Published by AIP Publishing.

DOI： 10.1063/1.5025870

Language：English   Publishing type：Research paper (scientific journal)  

A four-level model consisting of a higher triplet excited state (T-2), the lowest singlet and triplet excited states (S-1 and T-1), and the ground state was previously used to understand emission properties of a thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). In this report, we discuss the four-level model in more detail and apply to the other two TADF emitters, i.e., 1,2,4,5-tetrakis(carbazol-9-yl)-3,6-dicyanobenzene (4CzTPN) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene(2CzPN), in order to determine their excited-state structures. It is suggested that in all the emitters T-2 lies between S-1 and T-1 and play an essential role in the emitting process. In 4CzTPN, phosphorescence from T-2 is clearly observed around 100 K as in 4CzIPN. Compared to the other two emitters, 2CzPN has a wider energy gap between S-1 and T-1 so that delayed fluorescence at room temperature is thought to be mixed with phosphorescence. Because of this mixing, the spectrum characteristic of phosphorescence from T-2 in 2CzPN cannot be identified. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

DOI： 10.1117/1.JPE.8.032104

Language：English   Publishing type：Research paper (scientific journal)  

The molecular orientation in organic semiconductor films determines device performances. In particular, the spontaneous orientation of a permanent dipole moment (PDM) along the surface normal direction induces a polarization charge at the hetero-interfaces of stacked multilayer devices, and the interface charge dominates the charge accumulation and injection properties. Spontaneous orientation polarization (SOP) has been observed in the "randomly oriented" films of several organic semiconductor materials, and is potentially inherent in many common materials. Herein, we report that 11 additional molecules of organic light-emitting diode materials, including thermally activated delayed fluorescence emitters, and horizontally oriented emitters and electron transporters, exhibit SOP in their evaporated films. The experimental results clearly indicate that SOP frequently occurs in "horizontally oriented" films as well as "randomly oriented" films. The factors contributing to SOP formation are discussed in terms of the figure of merit per PDM. We found that strong intermolecular interactions tend to reduce the figure of merit. Moreover, we suggest the impact of SOP on device performances.

DOI： 10.1016/j.orgel.2018.04.026

Language：English  

DOI： 10.7567/JJAP.57.03E001

Language：English   Publishing type：Research paper (scientific journal)  

Long-lived triplet excitons on organic molecules easily deactivate at room temperature because of the presence of thermally activated nonradiative pathways. This study demonstrates long-lived phosphorescence at room temperature resulting from suppression of the nonradiative deactivation of triplet excitons in conventional organic semiconducting host-guest systems. The nonradiative deactivation pathway strongly depends on the triplet energy gap between the guest emitting molecules and the host matrices. The triplet energy gap required to confine the long-lived triplet excitons (approximate to 0.5 eV) is much larger than that of conventional host-guest systems for phosphorescent emitters. By effectively confining the triplet excitons, this study demonstrates long-lived room-temperature phosphorescence under optical and electrical excitation.

DOI： 10.1002/adfm.201703902

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.7567/JJAP.56.05E001

Language：English   Publishing type：Research paper (scientific journal)  

The photoluminescence properties of a thermally activated delayed fluorescence emitter, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), doped in a host matrix consisting of 1,3-bis(9-carbazolyl) benzene and a polar inert molecule, camphoric anhydride (CA), in various concentrations have been investigated. It is found that the addition of CA stabilizes only the lowest singlet excited state (S-1) of 2CzPN without changing the energy level of the lowest triplet excited state (T-1), leading to a reduction in the energy gap between S-1 and T-1. The maximum reduction of energy gap achieved in this work has been determined to be around 65 meV from the shift of the fluorescence spectrum and the temperature dependence of the photoluminescence decay rate.

DOI： 10.1186/s11671-017-2012-1

Language：English   Publishing type：Research paper (scientific journal)  

The temperature dependences of photoluminescence (PL) decay rates and the PL spectrum of a thermally activated delayed-fluorescence emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), are investigated. It is found that not only the lowest singlet (S-1) and triplet ( T-1) excited states but also an additional triplet excited state ( T-n) lying between S-1 and T-1 play an important role in the exciton decay process, particularly around 100 K. At around this temperature, some of the triplet excitons are thermally activated into Tn but not up to S-1, and they then decay into the ground state (S-0) with phosphorescence emission. Therefore, two kinds of phosphorescence, originating from T-n and T-1, are observed. The temperature dependence of the PL decay rates of 4CzIPN can be explained by a four-level model consisting of S-1, T-1, T-n, and S-0, and its energy gaps between T-n and T-1 and between S-1 and T-1 are determined to be 45 +/- 5 meV and 135 +/- 10 meV, respectively.

DOI： 10.1103/PhysRevApplied.7.034002

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/adom.201600006

Language：English  

Currently, organic light-emitting diodes (OLEDs) have reached the stage of commercialization, and there has been an intense drive to use them in various applications from small-and medium-sized mobile devices to illumination equipment and large television screens. In particular, room-temperature phosphorescent materials have become core OLED components as alternatives to conventionally used fluorescent materials because devices made with phosphorescent materials exhibit excellent light-emitting performance with internal electroluminescence efficiencies (η_int) of nearly 100 &#37;. However, phosphorescent materials have several intrinsic problems, such as being limited to metal-organic compounds containing rare metals, for example, Ir, Pt, Au, and Os, and difficulty in realizing stable blue light emission. As a result, researchers have attempted to develop new materials for use as emissive dopants in OLEDs that overcome these limitations. In this chapter, first we briefly review the progress of OLED materials and device architectures mainly based on fluorescent (first-generation) and phosphorescent (secondgeneration) emitters. Then, we discuss third-generation OLEDs that use a new light-emitting mechanism called thermally activated delayed fluorescence (TADF). Recently, highly efficient TADF, which had been difficult to realize with conventional molecular design, has been achieved by very sophisticated molecular structures, allowing access to the unlimited freedom of molecular design using carbon-based materials. This has led to the production of ultimate OLEDs that are made of common organic compounds without precious metals and can convert electricity to light at η_int of nearly 100 &#37;.

DOI： 10.1007/978-4-431-55654-1_2

Language：English   Publishing type：Research paper (scientific journal)  

We investigated differences between the transient state and steady state exciton-exciton annihilation rates based on Forster-type energy transfer. The exciton-exciton annihilation rate of an organic semiconductor is usually determined by transient state photoluminescence measurements using a pulsed laser or steady state photoluminescence measurements using a continuous wave laser. However, it is unclear that the respective annihilation rates determined by their rate equations are the same. In calculations with platinum-octaethylporphyrin (PtOEP) parameters, Monte Carlo simulations gave two different annihilation rates for the transient state and the steady state. The analytical models based on Forster-type energy transfer also showed the same result. These results indicate that the exciton-exciton annihilation rates in transient state and steady state are distinguished. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.071601

Language：English   Publishing type：Research paper (scientific journal)  

A strategy for designing highly efficient thermally activated delayed fluorescence (TADF) emitters was reported. TADF emitters with donor-acceptor-donor (D-A-D)-type structures showed highly efficient TADF because of their small singlet-triplet energy gap and large oscillator strength. An organic light-emitting diode containing a D-A-D-type TADF emitter, cis-BOX2, exhibited a high external electroluminescence quantum efficiency of 17.6&#37;.

DOI： 10.1246/cl.141054

Language：English   Publishing type：Research paper (scientific journal)  

We report on the charge carrier dynamics and their degradation phenomena in an organic light-emitting diode (OLED) doped by a thermally activated delayed fluorescence emitter; (4s, 6s)-2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN). Displacement current measurement (DCM) data revealed the presence of negative interface charge originating from the spontaneous orientation polarization of the electron transport layer (ETL), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene. The negative interface charge acts as a hole reservoir and thus confines the recombination zone near the emission layer (EML); 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP):4CzIPN (5 wt&#37;)/ETL interface. By keeping the recombination zone far from the hole transport layer, 4,40-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl (alpha-NPD), a better electroluminescence efficiency is expected because the Dexter energy transfer from the triplet state of 4CzIPN to that of alpha-NPD is suppressed. Moreover, we found an excellent linear relation between the accumulated hole amount and luminance losses owing to device aging. The results are consistent with hole traps originating at the degradation products of CBP as the main factor of device degradation. We suggest device architectures based on the charge carrier dynamics for better efficiency and lifetime. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2014.12.009

Language：English   Publishing type：Research paper (scientific journal)  

The influence of the host molecules on the photoluminescent (PL) and electroluminescent (EL) properties of organic light-emitting diode (OLED) emitters showing efficient thermally-activated delayed fluorescence (TADF) has yet to be investigated in detail. Here we demonstrate that the choice of host can cause large variations in the PL quantum yield (Phi(PL) similar to 15-70&#37;) and delayed PL transient decay (tau(del) similar to 2-70 ms) of a spiro-acridine-based TADF guest. We show that the effect of exciplex formation on Phi(PL) must be considered even at low concentrations of the TADF guest. Using the same TADF guest but changing the host layer, we are able to greatly vary the PL transient decay time from similar to 4 to similar to 70 ms while maintaining a high Phi(PL) similar to 70&#37;, which can lead to new applications. Detailed spectral characterization during PL decay reveals a gradually increasing singlet-triplet energy gap (Delta E-ST) as the origin of these observations. The time-varying Delta E-ST is explained based on dipole interactions between the host and guest molecules. Finally, PL and electrical considerations for host selection are discussed based on the performance of OLED devices. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2014.05.027

Language：English   Publishing type：Research paper (scientific journal)  

Using steady-state and time-resolved photoluminescence (PL) spectroscopy, we have investigated the temperature dependence of PL properties of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), which have a small energy gap between its singlet and triplet excited states and thus exhibits efficient thermally activated delayed fluorescence [H. Uoyama et al., Nature 492, 235 (2012)]. Below around 100 K, PL quantum efficiency of 4CzIPN thin films is largely suppressed and strong photoexcitation intensity dependence appears. These features can be explained by using rate equations for the densities of singlet and triplet excited states considering a triplet-triplet annihilation process. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4878397

Language：English   Publishing type：Research paper (scientific journal)  

We reduced the amplified spontaneous emission (ASE) threshold in an organic semiconductor laser structure by the introduction of an exciton blocking layer adjacent to the cathode layer. A phenyldipyrenylphosphine oxide (POPy2) layer with the function of an electron transport layer and the exciton blocking layer were inserted between an active layer of 4,4-bis[N-(carbazole)styrylbiphenyll (BSB-Cz) and a metal cathode layer. The electron injection barrier from POPy2 to BSB-Cz is downward, indicating no net energy barrier, and the hole injection barrier from the BSB-Cz layer into the POPy2 layer is also small because of the similarity between the highest occupied molecular orbital levels of the materials. Therefore, the proposed device structure can avoid extra carrier accumulations at the heterointerface, leading to compatibility in terms of both relaxation of the exciton-polaron annihilation and blocking of the energy transfer from the BSB-Cz layer into the cathode layer. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2013.04.001

Language：English   Publishing type：Research paper (scientific journal)  

DOI： http://authors.elsevier.com/sd/article/S0022231313002123

Language：English   Publishing type：Research paper (scientific journal)  

The temperature dependence of luminescence from [Cu(dnbp)(DPEPhos)]BF4 (dnbp = 2,9-di-n-butylphenanthroline, DPEPhos = bis[2-(diphenylphosphino)phenyl]ether) in a poly(methyl methacrylate) (PMMA) film indicates the presence of long-life green emission arising from two thermally equilibrated charge transfer (CT) excited states and one non-equilibrated triplet ligand center (3LC) excited state. At room temperature, the lower triplet CT state is found to be the predominantly populated excited state, and the zero-zero energy of this state is found to be 2.72 eV from the onset of its emission at 80 K. The tunable emission maximum of [Cu(dnbp)(DPEPhos)]BF4 in various hosts with different triplet energies is explained in terms of the multiple triplet energy levels of this complex in amorphous films. Using the high triplet energy charge transport material as a host and an exciton-blocking layer (EBL), a [Cu(dnbp)(DPEPhos)]BF4 based organic light-emitting diode (OLED) achieves a high external quantum efficiency (EQE) of 15.0&#37;, which is comparable to values for similar devices based on Ir(ppy)3 and FIrpic. The photoluminescence (PL) and electroluminescence (EL) performance of green emissive [Cu(mu I)dppb]2 (dppb = 1,2-bis[diphenylphosphino]benzene) in organic semiconductor films confirmed its 3CT state with a zero-zero energy of 2.76 eV as the predominant population excited state.

DOI： 10.1002/adfm.201101907

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

We demonstrate that horizontally oriented organic semiconducting molecules in amorphous films can be oriented uniaxially by mechanical brushing. The absorption of polarized light in the direction parallel to the brushing direction was higher than the absorption in the perpendicular direction. Thus, simultaneous uniaxial and in-plane molecular orientation in amorphous films was realized by brushing. In addition, we demonstrate a polarized electroluminescence from the films treated by mechanical brushing. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3608315]

DOI： 10.1063/1.3608315

Language：English   Publishing type：Research paper (scientific journal)  

Organic light-emitting diodes containing a liquid-emitting layer that exhibit improved external electroluminescence quantum efficiency (Phi(EL)) and maximum luminance are presented. Doping the liquid-emitting layer with an electrolyte significantly decreases the turn-on voltage for electroluminescence. Insertion of a TiO2 hole-blocking layer between the liquid-emitting layer and indium tin oxide cathode improves Phi(EL).

DOI： 10.1002/adma.201003505

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we introduce a time-correlated single photon counting system and an efficient light-collection system for studying fluorescence emitters under high-vacuum conditions; the latter system has an immersion objective, and an ionic liquid is used as a refractive index matching medium. The ionic liquid is positioned in high vacuum. The time-correlated single photon counting system has modified photomultiplier tubes that act as photon detectors. The light-collection system is designed to be simple, compact, and easy to use. In order to verify the performance of these systems, the optical properties of colloidal semiconductor nanocrystals (CdSe/ZnS) and fluorescent dye molecules are studied as examples. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.07.002

Language：English   Publishing type：Research paper (scientific journal)  

Nearly perfect pentacene single crystals with wide terraces several micrometers in width were grown by crystallization from a pentacene-containing trichlorobenzene solution. Organic Field-effect transistors (OFETs) were fabricated with the pentacene single crystals and characterized for their electrical properties. The field effect mobility was found to be in the range of 0.4-0.6 cm(2)/V.s, which is comparable to that of OFETs fabricated with pentacene single crystals prepared by a physical vapor-phase growth method. The results described in this paper clearly demonstrate that the crystallization of organic semiconductors from solution is a promising chemical method for device processing of OFETs.

DOI： 10.1021/la900647y

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we introduce a modified inverted microscope system in which an objective with high NA (0.95) is located under high-vacuum conditions, and a time-correlated single photon counting system is used along with a modified photomultiplier tube for the characterization of single emitters under high-vacuum conditions. The modified inverted microscope system is designed to be simple, compact, and easy to handle. As an example, the optical properties of individual colloidal semiconductor nanocrystals (CdSe/ZnS) were studied by using these systems. (c) 2008 Elsevier B.V. All rights reserved

DOI： 10.1016/j.tsf.2008.09.029

Language：English   Publishing type：Research paper (scientific journal)  

Organic light-emitting diodes (OLEDs) having various guest molecules doped in an organic host matrix layer are fabricated [the OLED structure is anode/hole-transporting layer (HTL)/guest-host emitting layer/hole-blocking layer/electron-transporting layer/cathode], and the dependence of current density-voltage (J-V) characteristics of the OLEDs on highest occupied molecular orbital (HOMO) levels of guest molecules are investigated. From the J-V characteristics of these OLEDs, we find two important results: (1) J-V characteristics of the OLEDs are controlled by the direct hole injection from the neighboring HTL to guest molecules, and (2) HOMO level alignment between the HTL and guest molecules provides efficient hole injection at this interface. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.01.010

Language：English   Publishing type：Research paper (other academic)  

We accurately measured the absolute photoluminescence (PL) quantum efficiency (eta(PL)) Of organic solid-state thin films by using an integrating sphere. We measured the eta(PL) Of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq(3)), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4,4'-bis(carbazol-9-yl)-2,2'-biphenyl [Ir(ppy)(3):CBP] co-deposited film. Alq(3) and lr(ppy)(3):CBP showed a eta(PL) = 20 +/- 1% and 97 +/- 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-N,C-3'] (acetylacetonato) iridium(III) [BtP(2)Ir(acac)] with CBP, and the blue complex, bis[(4,6-difluorophenyl)pyridinato -N, C-2](picolinato)iridium(III)[FIrpic], with m-bis(N-carbazolyl)benzene. The maximum eta(PL) values for BtP(2)Ir(acac), and FIrpic were 51 +/- 1 % (at 1.4mol%), and 99 +/- 1% (1.2mol%), respectively. These results suggest that the TIEL of red phosphorescent OLEDs using BtP(2)Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.1867555

Language：English   Publishing type：Research paper (scientific journal)  

Unusual phosphorescence characteristics of Ir(ppy)3 in a solid matrix at low temperatures
We observed unusual radiative decay characteristics of a (fac-tris(2-phenylpyridine)iridium [Ir(ppy)3]) triplet-excited state doped into 4, 4&#36;'&#36;-N, N&#36;'&#36;-dicarbazole-biphenyl (CBP) and polymethylmethacrylate (PMMA) host matrices. From a measurement of the temperature dependence on the phosphorescence intensity and the lifetime of Ir(ppy)3 in these hosts, we observed that phosphorescence intensities are independent of temperature, while the lifetimes significantly increase at temperatures below &#36;T sim 50&#36; K. These results lead us to conclude that the non-radiative transition rate (&#36;k_{ ext{nr } }&#36;) from the triplet excited state is very small compared with the radiative transition rate (&#36;k_{ ext{r } }&#36;) and that the phosphorescence quantum yield (&#36;phi_{ ext{PH } }&#36;) is nearly 100&#37; even at room temperature. Based on our experimental results, we propose a possible decay mechanism to rationalize the characteristic temperature dependence on the transient phosphorescence.

DOI： 10.1143/JJAP.43.L937

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.1751232

Language：Japanese   Publishing type：Research paper (scientific journal)  

High Efficiency White Electrophosphorescence Mechanism with Two Phosphorescent Dopants
High efficiency white organic light emitting diodes (WOLED) have been expected for applications of lighting, illumination and back-light sources for LCD. Recently, since organic phosphors demonstrated very high electroluminescence (EL) quantum efficiency of ˜100%, high efficiency WOLED with the organic phosphors has been anticipated. In this study, we employed an emitter layer which is doped with blue and red phosphorescence molecules. In our optimized device structure, we obtained maximum EL quantum efficiency of 4%. However, the shapes of the EL spectrum were strongly dependent on current density. With analysis of exciton decay process under optical and electrical excitations, we conclude that triplet-triplet annihilation occurs in blue and red phosphors independently, resulted in a significant change of the EL spectrum. Thus, the coincidence of the lifetimes of the blue and red phosphors is indispensable to escape change of EL spectrum with current density.

DOI： 10.1541/ieejfms.124.414

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.1695091

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/cm034689t

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京工業大学   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京工業大学   Country：Japan  

Event date： 2018.9 - 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2018.9 - 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋国際会議場   Country：Japan  

Event date： 2018.9 - 2019.9

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Venue：名古屋国際会議場   Country：Japan  

Event date： 2017.3

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Venue：横浜市・パシフィコ横浜   Country：Japan  

Event date： 2017.3

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Venue：横浜市・パシフィコ横浜   Country：Japan  

Event date： 2017.3

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Venue：横浜市・パシフィコ横浜   Country：Japan  

Event date： 2016.9

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Venue：新潟市・朱鷺メッセ   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市・朱鷺メッセ   Country：Japan  

Event date： 2015.9

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Venue：東北大学   Country：Japan  

Event date： 2014.11

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Venue：イーグレひめじ   Country：Japan  

Event date： 2014.8 - 2014.3

Language：English  

Venue：San Diego Convention Center   Country：United States  

Event date： 2014.7

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：UDX カンファレンス（東京・秋葉原）   Country：Japan  

Event date： 2014.3 - 2012.3

Language：English  

Venue：ACROS Fukuoka   Country：Japan  

Event date： 2014.2 - 2012.2

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Event date： 2013.9

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Event date： 2012.12

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Venue：Boston   Country：United States  

Event date： 2012.9

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Venue：愛媛大学・松山大学   Country：Japan  

Event date： 2012.6

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Venue：日本科学未来館   Country：Japan  

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Venue：早稲田大学   Country：Japan  

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Event date： 2011.12

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Event date： 2011.8 - 2011.9

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Venue：山形大学   Country：Japan  

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Venue：山形大学   Country：Japan  

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Venue：神奈川工科大学   Country：Japan  

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Venue：東京理科大学 森戸記念館   Country：Japan  

Event date： 2010.11 - 2010.12

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Venue：Boston   Country：United States  

Event date： 2010.11 - 2010.12

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Venue：Boston   Country：United States  

Event date： 2010.11 - 2010.12

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Event date： 2010.9

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Venue：長崎大学   Country：Japan  

Event date： 2010.9

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Venue：長崎大学   Country：Japan  

Event date： 2010.9

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Venue：長崎大学   Country：Japan  

Event date： 2010.9

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Venue：長崎大学   Country：Japan  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：9

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：12

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：10

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：12

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.