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3. Development of Cu–In–Ga–S quantum dots with a narrow emission peak for red electroluminescence.

Author

Jiang, Chang, Tozawa, Makoto, Akiyoshi, Kazutaka, Kameyama, Tatsuya, Yamamoto, Takahisa, Motomura, Genichi, Fujisaki, Yoshihide, Uematsu, Taro, Kuwabata, Susumu, and Torimoto, Tsukasa

Subjects
QUANTUM dots, STOKES shift, ELECTROLUMINESCENCE, QUANTUM dot devices, COPPER, BAND gaps, LIGHT emitting diodes, CHROMATICITY
Abstract

Narrowing the emission peak width and adjusting the peak position play a key role in the chromaticity and color accuracy of display devices with the use of quantum dot light-emitting diodes (QD-LEDs). In this study, we developed multinary Cu–In–Ga–S (CIGS) QDs showing a narrow photoluminescence (PL) peak by controlling the Cu fraction, i.e., Cu/(In+Ga), and the ratio of In to Ga composing the QDs. The energy gap of CIGS QDs was enlarged from 1.74 to 2.77 eV with a decrease in the In/(In+Ga) ratio from 1.0 to 0. The PL intensity was remarkably dependent on the Cu fraction, and the PL peak width was dependent on the In/(In+Ga) ratio. The sharpest PL peak at 668 nm with a full width at half maximum (fwhm) of 0.23 eV was obtained for CIGS QDs prepared with ratios of Cu/(In+Ga) = 0.3 and In/(In+Ga) = 0.7, being much narrower than those previously reported with CIGS QDs, fwhm of >0.4 eV. The PL quantum yield of CIGS QDs, 8.3%, was increased to 27% and 46% without a PL peak broadening by surface coating with GaSx and Ga–Zn–S shells, respectively. Considering a large Stokes shift of >0.5 eV and the predominant PL decay component of ∼200–400 ns, the narrow PL peak was assignable to the emission from intragap states. QD-LEDs fabricated with CIGS QDs surface-coated with GaSx shells showed a red color with a narrow emission peak at 688 nm with a fwhm of 0.24 eV. [ABSTRACT FROM AUTHOR]

Published
2023
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8. Ambipolar transport in bulk crystals of a topological insulator by gating with ionic liquid

Author

Segawa, Kouji, Ren, Zhi, Sasaki, Satoshi, Tsuda, Tetsuya, Kuwabata, Susumu, and Ando, Yoichi

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We report that the ionic-liquid gating of bulk single crystals of a topological insulator can control the type of the surface carriers and even results in ambipolar transport. This was made possible by the use of a highly bulk-insulating BiSbTeSe2 system where the chemical potential is located close to both the surface Dirac point and the middle of the bulk band gap. Thanks to the use of ionic liquid, the control of the surface chemical potential by gating was possible on the whole surface of a bulk three-dimensional sample, opening new experimental opportunities for topological insulators. In addition, our data suggest the existence of a nearly reversible electrochemical reaction that causes bulk carrier doping into the crystal during the ionic-liquid gating process., Comment: 7 pages, 6 figures, 2 tables; significantly expanded version to fully discuss the gating process and its side effects; published in PRB

Published
2012
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9. Electrochemical synthesis and superconducting phase diagram of Cu_xBi2Se3

Author

Kriener, M., Segawa, Kouji, Ren, Zhi, Sasaki, Satoshi, Wada, Shohei, Kuwabata, Susumu, and Ando, Yoichi

Subjects
Condensed Matter - Superconductivity
Abstract

The superconducting Cu_xBi_2Se_3 is an electron-doped topological insulator and is a prime candidate of the topological superconductor which still awaits discovery. The electrochemical intercalation technique for synthesizing Cu_xBi2Se3 offers good control of restricting Cu into the van-der-Waals gap and yields samples with shielding fractions of up to ~50%. We report essential details of this synthesis technique and present the established superconducting phase diagram of T_c vs x, along with a diagram of the shielding fraction vs x. Intriguingly, those diagrams suggest that there is a tendency to spontaneously form small islands of optimum superconductor in this material., Comment: 6 pages, 4 figures

Published
2011
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10. Spectrally narrow band-edge photoluminescence from AgInS2-based core/shell quantum dots for electroluminescence applications.

Author

Uematsu, Taro, Izumi, Ryunosuke, Sugano, Shoki, Sugano, Riku, Hirano, Tatsuya, Motomura, Genichi, Torimoto, Tsukasa, and Kuwabata, Susumu

Abstract

This study presents a facile synthesis of cadmium-free ternary and quaternary quantum dots (QDs) and their application to light-emitting diode (LED) devices. AgInS2 ternary QDs, developed as a substitute for cadmium chalcogenide QDs, exhibited spectrally broad photoluminescence due to intrinsic defect levels. Our group has successfully achieved narrow band-edge PL by a coating with gallium sulfide shell. Subsequently, an intrinsic difficulty in the synthesis of multinary compound QDs, which often results in unnecessary byproducts, was surmounted by a new approach involving the nucleation of silver sulfide followed by material conversion to the intended composition (silver indium gallium sulfide). By fine-tuning this reaction and bringing the starting material closer to stoichiometric compositional ratios, atom economy was further improved. These QDs have been tested in LED applications, but the standard device encountered a significant defective emission that would have been eliminated by the gallium sulfide shells. This problem is addressed by introducing gallium oxide as a new electron transport layer. [ABSTRACT FROM AUTHOR]

Published
2024
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13. Basolateral Mg2+ extrusion via CNNM4 mediates transcellular Mg2+ transport across epithelia: a mouse model.

Author

Yamazaki, Daisuke, Funato, Yosuke, Miura, Jiro, Sato, Sunao, Toyosawa, Satoru, Furutani, Kazuharu, Kurachi, Yoshihisa, Omori, Yoshihiro, Furukawa, Takahisa, Tsuda, Tetsuya, Kuwabata, Susumu, Mizukami, Shin, Kikuchi, Kazuya, and Miki, Hiroaki

Subjects
Epithelium, Animals, Mice, Knockout, Humans, Mice, Amelogenesis Imperfecta, Retinitis Pigmentosa, Hypertrichosis, Disease Models, Animal, Magnesium, Cation Transport Proteins, Biological Transport, Mutation, Missense, Leber Congenital Amaurosis, Disease Models, Animal, Knockout, Mutation, Missense, Genetics, Developmental Biology
Abstract

Transcellular Mg(2+) transport across epithelia, involving both apical entry and basolateral extrusion, is essential for magnesium homeostasis, but molecules involved in basolateral extrusion have not yet been identified. Here, we show that CNNM4 is the basolaterally located Mg(2+) extrusion molecule. CNNM4 is strongly expressed in intestinal epithelia and localizes to their basolateral membrane. CNNM4-knockout mice showed hypomagnesemia due to the intestinal malabsorption of magnesium, suggesting its role in Mg(2+) extrusion to the inner parts of body. Imaging analyses revealed that CNNM4 can extrude Mg(2+) by exchanging intracellular Mg(2+) with extracellular Na(+). Furthermore, CNNM4 mutations cause Jalili syndrome, characterized by recessive amelogenesis imperfecta with cone-rod dystrophy. CNNM4-knockout mice showed defective amelogenesis, and CNNM4 again localizes to the basolateral membrane of ameloblasts, the enamel-forming epithelial cells. Missense point mutations associated with the disease abolish the Mg(2+) extrusion activity. These results demonstrate the crucial importance of Mg(2+) extrusion by CNNM4 in organismal and topical regulation of magnesium.

Published
2013

28. Photoluminescence properties of quinary Ag–(In,Ga)–(S,Se) quantum dots with a gradient alloy structure for in vivo bioimaging

Author

Rismaningsih, Nurmanita, Yamauchi, Hiroki, Kameyama, Tatsuya, Yamamoto, Takahisa, Morita, Saho, Hiroshi, Yukawa, Uematsu, Taro, Yoshinobu, Baba, Kuwabata, Susumu, and Torimoto, Tsukasa

Abstract

Multinary semiconductor quantum dots (QDs) composed of group I–III–VI elements have received much attention for wide-ranging applications due to their low level of toxicity and tunable optical properties. The chemical composition and particle size are important parameters for controlling the physicochemical properties of these QDs. In this study, we prepared quinary QDs of an Ag–(In,Ga)–(S,Se) semiconductor (AIGSSe) by thermolysis of precursors in an organic solution with two-step heat treatment and evaluated their physicochemical properties as a function of Se fraction. The energy gap (Eg) of QDs decreased from 1.9 to 1.5 eV with an increase in the Se/(S + Se) ratio from 0 to 1, accompanied by a shift of the valence band maximum to a higher energy level. The obtained AIGSSe QDs exhibited a sharp band-edge PL peak, the wavelength of which was red-shifted from 580 to 790 nm with a decrease in their Eg. The PL intensity was remarkably enlarged by the surface coating with a GaSx shell, the highest PL quantum yield being 50% for the PL peak at 580 nm. AIGSSe QDs with an Se/(S + Se) ratio of 0.50 exhibited a near-IR PL peak at 790 nm, which is suitable for in vivo bioimaging in the wavelength range of the first biological window. By incorporating GaSx-coated AIGSSe QDs (Se/(S + Se) = 0.50) into liposomes, the QDs were transferred into aqueous solutions without significant deterioration of both the PL peak outline and quantum yield, though a broad PL peak originating from defect sites appeared with a relatively large PL intensity when GaSx-coated Ag–(In,Ga)–S QDs that did not contain Se were used. In vivo imaging of a mouse was successfully performed by detecting the band-edge emission at 790 nm of AIGSSe QDs injected subcutaneously in the back of the mouse.

Published
2021

31. Bright Red Luminescence from Ag–In–Ga–S-Based Quantum Dots with the Introduction of Copper

Author

Uematsu, Taro, Krobkrong, Navapat, Asai, Kenichiro, Motomura, Genichi, Fujisaki, Yoshihide, Torimoto, Tsukasa, and Kuwabata, Susumu

Abstract

This study presents cadmium-free, red-emission quantum dots (QDs) synthesized by incorporating Cu into silver indium gallium sulfide/gallium sulfide (Ag–In–Ga–S/Ga–S) core/shell QDs. By using a previous technique, in which the original Ag–In–Ga–S/Ga–S core/shell QDs exhibiting band-edge photoluminescence (PL) were improved to achieve a narrower emission and facile synthesis, we injected a mixture of Cu and Ag sources into a heated solution containing In, Ga, and S sources. This resulted in the formation of Ag–Cu–In–Ga–S quinary QDs without any precipitation. After being coated with a Ga–S shell, these QDs exhibit a red PL with a spectral full-width at half maximum of 55–60 nm. Although the PL wavelength was responsive to changes in In/Ga ratios, it was unaffected by variations in Cu/Ag ratios due to the transition between conduction band electrons and holes localized at Cu cites. Notably, the electroluminescence device exhibited high-purity red light that satisfies the recommendation ITU-R BT.2020 standard.Cadmium-free Ag–Cu–In–Ga–S/Ga–S core/shell quantum dots were synthesized by a scalable method and red emission was obtained from a free-to-bound transition via Cu-related localized states. The emission wavelength was controlled by the In/Ga ratio, which allowed the fabrication of high-purity red electroluminescence in compliance with the ITU-R BT.2020 standard.

Published
2023
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38. On-surface metathesis of an ionic liquid on Ag(111)

Author

Massicot, Stephen, Sasaki, Tomoya, Lexow, Matthias, Maier, Florian, Kuwabata, Susumu, and Steinrück, Hans-Peter

Subjects
On-surface metathesis, Solid Catalyst with Ionic Liquid Layer, Ionic Liquids, Angle-resolved X-ray photoelectron spectroscopy, Ultra-thin films, Catalysis
Abstract

We investigated the adsorption, surface enrichment, ion exchange, and on-surface metathesis of ultrathin mixed IL films on Ag(111). We stepwise deposited 0.5 ML of the protic IL diethylmethylammonium trifluoro­methanesulfonate ([dema][TfO]) and 1.0 ML of the aprotic IL 1-methyl-3-octylimidazolium hexa­fluoro­phosphate ([C8C1Im][PF6]) at around 90 K. Thereafter, the resul­ting layered frozen film was heated to 550 K, and the thermally induced phenomena were monitored in situ by angle-resolved X-ray photoelectron spectroscopy. Between 135 and 200K, [TfO]– anions at the Ag(111) surface are exchanged by [PF6]– anions and enriched together with [C8C1Im]+ cations at the IL/vacuum interface. Upon further heating, [dema][PF6] and [OMIm][PF6] desorb selectively at ~235 and ~380 K, respectively. Hereby, a wetting layer of pure [C8C1Im][TfO] is formed by on-surface metathesis at the IL/metal interface, which completely desorbs at ~480 K. For comparison, ion enrichment at the vacuum/IL interface was also studied in macroscopic IL mixtures, where no influence of the solid support is expected.

Published
2022

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